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RA

See

registration authority (RA)

rack

Also called an equipment rack, a metal frame for holding and organizing networking devices. A networking component that is designed to be mounted in a rack is said to be rack-mountable. Rack-mountable devices include hubs, routers, Ethernet switches, patch panels, and uninterruptible power supply (UPS) devices.

Racks can be wall mounted or freestanding. They come in various heights and standard widths—19 inches is by far the most common width. The width is the distance between the mounting holes for mounting equipment—the actual width of the rack is usually several inches wider. Common heights for racks are 48 and 83 inches. In EIA/TIA-compliant racks, the holes on the frame are spaced 1.75 inches apart vertically, a distance symbolized as a “U” or “unit” of rack space. If a piece of networking equipment is described as 3U, it occupies 3 x 1.75 = 5.25 inches of vertical space once it is mounted in the rack.

graphic r-1. rack.

Graphic R-1. Rack.

Racks offer a way to organize equipment in a wiring closet. Racks come with a variety of accessories. Cable organizers, for example, allow you to run bundled cabling down the side or back of the rack to avoid “spaghetti.” You can use sliding shelves or drawers to incorporate odd-sized equipment in racks for easy access for configuration and wiring. Vented sides and fan trays help circulate air to keep equipment from overheating. By attaching a locking plastic door, you can convert some racks into cabinets for more secure storage.

NOTE

A ladder rack is a modular rack system for supporting cable runs in walls, false floors, and false ceilings.

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If your area is prone to earthquakes, you can bolt the base of your rack to the floor for greater security. Wall-mounted racks allow you to organize equipment in areas with limited floor space.

See also cabinet, cabling

RADIUS

See Remote Authentication Dial-In User Service (RADIUS)

RAID

Stands for redundant array of independent disks, a technology for implementing fault tolerance on a disk subsystem by using data redundancy, either using software or using a separate hardware RAID storage unit.

A number of RAID levels are defined, but Microsoft Windows NT and Windows 2000 support only three of them—RAID 0, RAID 1, and RAID 5. These are the most popular implementations of RAID. The RAID levels that are presently defined include the following:

NOTE

RAID is implemented using the Windows NT Server administrative tool Disk Administrator or the Disk Management portion of the Computer Management tool in Windows 2000. RAID cannot be implemented on Windows NT Workstation or Windows 2000 Professional.

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Windows NT and Windows 2000 provide a software-based RAID solution in which the operating system software enables various types of RAID functionality on the internal disk subsystem, usually a Small Computer System Interface (SCSI) disk subsystem. The other type of RAID solution is hardware-based RAID, in which stand-alone external RAID-5 disk arrays are usually attached to servers using SCSI or fiber channel connections.

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When you buy a hardware RAID-5 unit, be sure that it has hot-rebuild, hot-swap, and hot-spare capabilities. These features protect business-critical data and ensure high availability.

See also fault tolerance

RAID-5 volume

In Microsoft Windows 2000, a volume created with the Disk Management portion of the Computer Management tool that stores its data with parity information across multiple physical disks. Data is stored using striping, which places data and parity information alternately and evenly across multiple disks. The parity information in RAID 5 is not stored on a single disk—each stripe stores its parity information on a different (rotating) disk. RAID-5 volumes provide fault tolerance, but they cannot be mirrored or extended. RAID-5 volumes must be created on dynamic disks.

NOTE

The Window NT and Windows 2000 equivalent of RAID-5 volumes are stripe sets with parity.

See also dynamic volume

RAS

See Remote Access Service (RAS)

RBOC

See Regional Bell Operating Company (RBOC)

rcp

A simple TCP/IP utility for copying files to or from remote hosts. Rcp uses Transmission Control Protocol (TCP) to ensure reliable delivery of data between the client and the host. Rcp can be scripted in a batch file and does not require a password. The remote host must be running the rshd service, and the user’s username must be configured in the remote host’s .rhosts file. Rcp is one of the r-commands available on all UNIX systems.

NOTE

Microsoft’s implementation of TCP/IP on Windows NT and Windows 2000 includes rcp client software but not rshd services.

rdisk

A Microsoft Windows NT utility for updating information in the %SystemRoot%\repair folder and creating an emergency repair disk (ERD). You can use the ERD to save the configuration of a server running Windows NT and to restore the server if the system files or registry become corrupted. Rdisk is not listed as a Windows NT administrative tool, but you can run it from the command prompt, from the Run command box (via the Start menu), or by creating a shortcut to the executable by using the path \Winnt\System32\rdisk.exe. When you run rdisk, you can either update the \Winnt\Repair directory or simply create an ERD. (You can create a Windows 2000 ERD from the Welcome tab of the Backup tool.)

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Rdisk.exe normally doesn’t back up the default, Security Account Manager (SAM), or security hives unless you run it with the /s switch. To do this, type rdisk /s at the command prompt or in the Run command box.

RDP

See Remote Desktop Protocol (RDP)

recipient

In Microsoft Exchange Server, any directory object that can receive messages. Recipients are generally stored in the Recipient container within the Exchange directory hierarchy. Types of recipients that you can create include the following:

recovery

The process of repairing a downed server, usually after a disk failure. Recovering a server usually involves these steps:

  1. Replacing the failed hardware that caused the server to crash

  2. Reinstalling the base operating system and any required service packs, along with any server applications that are needed

  3. Restoring critical data and configuration files from tape backup

In Microsoft Windows NT, you can configure recovery settings on the Startup/Shutdown tab on the property sheet of the System utility in Control Panel. (To configure recovery settings in Windows 2000, open the System utility in Control Panel, click the Advanced tab, and then click the Startup And Recovery button.) You use these settings to tell the server to dump debugging information or to log an event if a Stop screen occurs.

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To prepare for the possibility of a downed server, you should do the following:

Recreational Software Advisory Council (RSAC)

A nonprofit organization with a content advisory system for Web sites on the Internet. The system, known as RSACi (Recreational Software Advisory Council on the Internet), allows Web site administrators to rate their sites according to degrees of potentially objectionable content. There are four types of content, each with five levels, rated from 0 to 4. The content areas are as follows:

By rating their Web sites according to the RSACi system, Web site administrators can help adults protect children from content that might be objectionable. Microsoft Internet Explorer has built-in client support for the RSACi system, which is administered using a password-protection scheme.

On the Web

•

Recreational Software Advisory Council (RSAC) home page : http://www.rsac.org

recursive query

A Domain Name System (DNS) query in which a resolver contacts a name server to perform a name lookup and the name server returns a result or an error. The name server cannot refer the client to a different name server, but it can forward the query directly to another name server if it has a forwarder configured.

How It Works

When a name lookup is performed on a name server, the resolver sends a recursive query to a nearby name server. If the name is outside the name server’s zone of authority, the name server cannot resolve the name and returns an error unless it is also configured as a forwarder. If this is the case, the nearby name server performs an iterative query on a root name server, which then responds with the IP address of a name server whose zone of authority includes the desired top-level domain. Further iterative queries are performed until the name is resolved into its IP address or an error is produced.

See also inverse query, iterative query

redirection

A process whereby a Web server such as Internet Information Services (IIS) forwards a request for a file to a different directory, Web site, or application. Redirection enables client requests to always be fulfilled, even when content in a site is being updated or if the name of a virtual directory has been changed. For example, if you want to replace an old version of a page named old.htm with a newer version named new.htm, but you don’t want to alter the navigational structure of your site or bother users with a notice of the change, you can enter a <META> tag in the <HEAD> section of the old.htm file to redirect browsers to the new page.

For example, the following tag in the <HEAD> section of the old page causes a browser accessing that page to be redirected to the new page after viewing the old page for 3 seconds:

 <META HTTP-EQUIV="REFRESH" CONTENT="3;URL=NEW.HTM">

You can place a notice on the old page such as, “This page will be redirected to its newer version in 3 seconds.”

The term “redirection” is also used in printing. For example, if you are trying to print some documents but a print device has failed, Microsoft Windows 2000 lets you redirect all outstanding jobs for the print device to another print device that uses the same printer driver as the failed device. To redirect your pending documents, follow these steps:

  1. Open the property sheet for the failed print device, and select the Ports tab.

  2. Click the Add Port button, select Local Port, select New Port, and enter the Universal Naming Convention (UNC) path for the second print device.

  3. Click OK, and then click Apply.

redirection symbol

See > (the “greater than” symbol in the Numbers and Symbols chapter)

redirector

A networking software component installed on a client machine or workstation that allows a client to access file and print services on a network server. The redirector makes it appear to the client that the file and print resources are located on the local machine instead of elsewhere on the network.

How It Works

On a machine running Microsoft Windows NT or Windows 2000, the Workstation service is the default redirector. However, you can install multiple redirectors on a machine running Windows NT or Windows 2000 if you need connectivity to different file systems. In Windows NT and Windows 2000, the redirector is implemented in the form of a file system driver. When a client program requests a network resource, the request is handed to the I/O Manager, which calls the redirector. The redirector translates the request into Server Message Block (SMB) requests for transmission over the network to the Server service on the remote computer.

Regional Bell Operating Company (RBOC)

One of the regional telcos that was created as a result of the breakup of American Telephone and Telegraph (AT&T), or one of their successors. AT&T, which was also known as the Bell System (or “Ma Bell”), was divested in 1983 to end its monopoly control and was broken up into several dozen Bell Operating Companies (BOCs), each of which was to supply telephone services to local loop subscribers in a given geographical region. Seven Regional Bell Operating Companies (RBOCs) were also created, each consisting of two or more BOCs. The seven original RBOCs were Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Bell, Southwestern Bell, and U S WEST. RBOCs provided local loop services to much of the United States by functioning as local exchange carriers (LECs), while AT&T was left to provide long-distance carrier services and to function as an inter-exchange carrier (IXC). In addition to the RBOCs, dozens of independent LECs serviced different areas.

The telecommunications landscape changed with the passage of the Telecommunications Act of 1996. The act allowed RBOCs and independent LECs to compete with existing IXCs for long-distance carrier business, allowed mergers, and essentially opened up the telecommunications market to all kinds of companies, including cable television companies. Of the seven original RBOCs, only five remain today.

registration authority (RA)

A company or organization that is responsible for receiving and validating requests for digital certificates and public/private key pairs. A registration authority (RA) is part of the public key infrastructure (PKI).

How It Works

The RA receives a certificate request and verifies the identity of the requestor using acceptable forms of identification, which can be communicated face to face, over the telephone, by mail or courier, or in another secure fashion that is acceptable to the RA. Identification can include a driver’s license, Social Security number, or another unique identifier for the requestor. If the RA approves the request, it contacts the certificate authority (CA) in the PKI and asks it to issue the requestor the desired digital certificate and key pair. The RA and CA are often different entities within the same company or organization.

See also public key cryptography, public key infrastructure (PKI)

registry

A hierarchical database in which newer Microsoft Windows operating systems store their hardware and software configuration information such as user profiles, the hardware and software installed on the system, registered document types, property settings for icons, ports being used, and so on. The registry in Windows 2000, Windows NT, Windows 95, and Windows 98 replaces the INI files, such as win.ini and system.ini, that were used in the legacy Windows 3.1 and Windows for Workgroups 3.11 operating systems.

How It Works

In Windows NT and Windows 2000, the registry is logically divided into five subtrees, each containing keys and subkeys (analogous to folders and subfolders) that themselves contain values (analogous to files). Physically, the registry consists of a series of hives and their transaction files located in %SystemRoot%\system32\config.

In Windows 95 and Windows 98, the logical structure of the registry is similar to that for Windows NT and Windows 2000, but the physical format is incompatible. A sixth subtree called HKEY_DYN_DATA is created dynamically and is used for performance measuring and Plug and Play configuration. The registry consists of dynamic information stored in RAM and two files in the %Win_Root% directory: system.dat, which stores computer-specific information, and user.dat, which stores user-specific information.

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The main tool you should use to modify the registry is Control Panel, which provides a number of utilities for safely configuring different aspects of the system’s hardware and installed software. If you want (or need) to dig deeper into the registry, use the registry editor, but do so carefully—a single wrong value can render your operating system unbootable.

Registry Checker

A Microsoft Windows 98 utility for troubleshooting registry problems. Registry Checker can correct certain kinds of registry problems and can back up the registry regularly.

How It Works

Registry Checker comes in two forms:

Registry Checker automatically inspects the registry upon startup and attempts to either fix the problem or restore the registry from backup. It automatically backs up the Windows 98 registry each day after a successful system startup and can maintain up to five different backup versions of the registry in compressed format. Registry Checker also improves system performance by removing information from the registry that is no longer needed and by compacting free space.

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To manually start Registry Checker, open the Start menu, point to Accessories and then System Tools, and choose System Information. In the Microsoft System Information window, select Registry Checker from the Tools menu.

registry editor

A tool for editing the Microsoft Windows registry. The registry editor for Windows 95 and Windows 98 is called regedit, and the registry editor for Windows NT and Windows 2000 is called regedt32.

Regedit lets you search for, create, modify, and delete keys and values in the local registry; connect to a remote computer running Windows 95 or Windows 98; view or modify the registry; and import and export portions of the registry as text files with the extension .reg.

Regedt32 lets you search for, create, modify, and delete keys and values on the local or remote computer; save and restore keys for backup purposes; modify permissions; and configure auditing of registry access.

graphic r-3. registry editor.

Graphic R-3. Registry editor.

NOTE

The Windows 95 and Windows 98 registry editor regedit is included in Windows NT and Windows 2000 in the %SystemRoot% directory, but you should avoid using it for editing the registry for these operating systems because it does not support all data types in the Windows NT and Windows 2000 registries.

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To avoid accidentally corrupting the registry, use the Options menu to set regedt32 to read-only mode unless you need to modify to the Windows NT or Windows 2000 registry.

To remotely modify the registry over the network on another machine running Windows 95 or Windows 98, you must have the Remote Registry service installed and user-level security enabled on the network.

If you make a mistake when you use the registry editor, your system might be rendered unbootable! Microsoft recommends against directly changing the registry if you can make the change using another method (such as using Control Panel).

relative path

The hierarchical path that locates a file or folder on a file system starting from the current directory. The relative path is different from the absolute path, which locates the file or folder starting from the root of the file system.

Example

If the current directory is C:\Windows, the relative path to the executable for the game of Solitaire, which is located in the current directory, is simply the name of the executable—sol.exe. If the current directory is C:\Windows\System, the relative path to Solitaire is ..\sol.exe.

In a UNIX file system, the syntax for relative paths is similar except that it uses forward slashes instead of backslashes to separate levels in the file system hierarchy.

NOTE

The idea of a “relative path” is also used in other naming contexts. For example, in Active Directory of Microsoft Windows 2000, you can uniquely and globally specify directory objects using the object’s distinguished name, which provides a kind of absolute path within the directory starting at the root and terminating at the desired object. For example, the object representing the user Mitch Tulloch in the domain northwind.expedia.com has this distinguished name:

 DC=com,DC=expedia,DC=northwind,OU=Users,CN=Mitch Tulloch

If a search context is established as the Users container within the northwind.expedia.com domain, the relative distinguished name of the Mitch Tulloch object is simply

 CN=Mitch Tulloch

This relative distinguished name uniquely identifies the desired object within the Users container in Active Directory.

See also absolute path

remailer

Also called an anonymous remailer, an Internet site that lets you forward Simple Mail Transfer Protocol (SMTP) e-mail to recipients anonymously. You can use remailers to ensure the privacy of your e-mail address—for example, to keep recipients from adding your address to a mailing list. You can also use remailers to prevent yourself from being spammed when you voice an unpopular opinion on a mailing list or some other forum.

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Yahoo! has a list of Web-based anonymous remailers.

remote access

Any networking technology that gives users access to essential network services from remote locations. Remote access to a company network can be either dial-up access through a modem or dedicated access through a leased line. Remote access typically gives remote users access to the following services on a company network:

How It Works

There are two basic types of remote access:

graphic r-4. remote access.

Graphic R-4. Remote access.

NOTE

Microsoft has enabled remote node remote access functionality on both its Windows NT and Windows 2000 operating system platforms to allow remote users to connect to a Windows NT–based or Windows 2000–based network. The Remote Access Service (RAS) of Windows NT provides full-featured remote node services for dial-up networking and virtual private network (VPN) functionality using the RAS and is administered using the administrative tool called Remote Access Admin. The optional Routing and Remote Access Service (RRAS) component for Windows NT 4 adds additional Internet Protocol (IP) routing functionality and is administered using its own tool called Routing and RAS Admin. On the Windows 2000 platform, both dial-up networking and VPN functionality are supported within Routing and Remote Access; they are administered by using either the netsh command-line utility or the Routing and Remote Access console.

A RAS server is often called a RAS router because it has at least one local area network (LAN) and one wide area network (WAN) interface and therefore operates as a router. The same is true of RRAS servers.

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In a mixed environment of Windows NT and Windows 2000 RAS and RRAS servers, there are limitations on which tools you can use for administering the various servers:

Remote Access Admin

An administrative tool in Microsoft Windows NT for managing and configuring the Remote Access Service (RAS) on servers running Windows NT. You can use this tool to

NOTE

The corresponding tool for administering remote access on the Windows 2000 Server platform is the Routing and Remote Access console.

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You can also grant a user permission to dial in to your network through RAS by using User Manager for Domains. Access the user’s properties and click the Dialin button.

Remote Access Service (RAS)

An optional Microsoft Windows NT networking service that provides remote access for remote clients. A machine running Windows NT on which Remote Access Service (RAS) is installed is called a RAS server.

How It Works

RAS allows remote clients to connect through a telephone line or other wide area network (WAN) link to the RAS server; from there RAS allows those clients to access resources on the network. Remote users can access network resources as though they were logged on to a machine directly connected to the network. To allow a user to connect remotely to the RAS server, use the administrative tool User Manager for Domains and grant the user dialin permission. You can set three forms of dialin permission:

RAS on Windows NT provides both dial-in and dial-out capability, supporting up to 256 simultaneous inbound connections on Windows NT Server but only one inbound connection on Windows NT Workstation. Clients that want to connect to a RAS server must have dial-up networking or a similar application installed. RAS is fully integrated into the Windows NT security model and supports encrypted authentication, auditing, callback, and intermediary hardware security hosts. Users can be restricted to access to the RAS server only, or to access through the RAS server to all resources on the network.

Windows NT RAS supports clients connecting over the following media:

You can establish RAS connections with Windows NT by using any common local area network (LAN) transport protocol and the following WAN protocols:

NOTE

An optionally available Windows NT 4 component called Routing and Remote Access Service (RRAS) replaces the existing RAS on Windows NT and provides additional Internet Protocol (IP) routing functionality.

On Windows 2000 Server, remote access functionality is provided by Routing and Remote Access, which supports both dial-up networking and virtual private networks.

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You install RAS on a Windows NT server by using the Services tab of the Network utility in Control Panel.

See also remote access, Routing and Remote Access, Routing and Remote Access Service (RRAS)

remote administration

The practice of administering network resources from a remote location. Remote administration capability is essential in an enterprise-level wide area network (WAN) environment and for network administrators who are on the road. Networking and software vendors offer many types of solutions for remote administration, including the following:

Remote Authentication Dial-In User Service (RADIUS)

A protocol for authentication, authorization, and accounting of remote access connections using dial-up networking and virtual private network (VPN) functionality. Remote Authentication Dial-In User Service (RADIUS) is typically implemented with the Point-to-Point Tunneling Protocol (PPTP).

How It Works

RADIUS is a client/server protocol that centralizes the profile information of dial-up users in a central database on a RADIUS server, which runs special RADIUS software. The RADIUS server is generally separate from the network access server (NAS) that actually allows the client to make a dial-up connection. An RFC-compliant RADIUS server stores all user profile information in a flat-file ASCII database that is accessible by any NAS that needs it to authenticate users. Some RADIUS servers can also use UNIX password files, Password Authentication Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP), Microsoft Challenge Handshake Authentication Protocol (MS-CHAP), third-party security systems, and Network Information Services (NIS) for authenticating users. This improves the security of remote access to corporate networks through tunneling across the Internet and simplifies administration of remote users. RADIUS servers are also typically used to provide statistics for billing purposes.

In a typical session, a client dials in to a NAS at an Internet service provider (ISP) and submits its credentials, which the NAS reformats as RADIUS packets and forwards to the RADIUS server. The RADIUS server can authenticate the user directly or act as a proxy client to forward the authentication process to some other type of service or security device. Once the RADIUS server authenticates the client, it informs the NAS, which allows the client to complete its connection. All communication between the client and the RADIUS server is encrypted.

graphic r-5. remote authentication dial-in user service (radius).

Graphic R-5. Remote Authentication Dial-In User Service (RADIUS).

NOTE

RADIUS is supported by the Internet Authentication Service (IAS).

Remoteboot service

An optional Microsoft Windows NT service for starting MS-DOS, Windows 3.1, Windows 95, and Windows 98 Remoteboot clients remotely over the network. These Remoteboot clients are diskless workstations that have a network interface card (NIC) with a boot programmable read-only memory (PROM) chip that allows them to be started remotely. The client operating system and client startup configuration files reside on the Remoteboot server, not on the client.

Remoteboot gives the administrator greater control over a user’s workstation but requires greater network bandwidth to work effectively. It reduces costs by eliminating the need for local hard drives or floppy drives on workstations. You use the Remoteboot Manager administrative tool to manage the Remoteboot service on a server running Windows NT and to add diskless workstations to your network, remove them from the network, and configure them.

remote bridge

A bridge that connects two geographically separated networks by using a telecommunications service such as Plain Old Telephone Service (POTS), leased lines, or a circuit-switched service. A remote bridge has at least one local area network (LAN) port, such as an RJ-45 jack for an unshielded twisted-pair (UTP) LAN connection to a switch or a hub, and at least one serial port, such as an RS-232 port or V.35 interface. The serial port is synchronous for digital lines or asynchronous for modems. The bridge might have both synchronous and asynchronous serial ports. Remote bridges can also be enabled for Simple Network Management Protocol (SNMP) and have other diagnostic and support features such as out-of-band management (OBM) support.

graphic r-6. remote bridge.

Graphic R-6. Remote bridge.

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To use remote bridges to connect remote LANs, connect a bridge to the main hub or switch in each LAN, and then connect the serial port on each bridge to the modem, Integrated Services Digital Network (ISDN) terminal adapter, or Channel Service Unit/Data Service Unit (CSU/DSU), depending on the type of wide area network (WAN) link used.

See also bridge

remote client impersonation

A technique for attacking or gaining improper access to a network. Remote client impersonation takes place when a third party monitors traffic on a network by using a packet sniffer or software such as Microsoft Network Monitor, captures a connection during the user authentication process, extracts the authentication parameters (such as username, password, and domain) from the captured frames, and then takes control of the authenticated connection.

A similar hacking technique called a replay attack takes place when a third party monitors traffic on a network, captures a connection during the authentication process, and then plays back the client’s captured response to obtain a new authenticated connection.

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Authentication schemes in which the user’s password is transmitted in clear text, such as the Password Authentication Protocol (PAP) supported by most Point-to-Point Protocol (PPP) services, are most susceptible to remote client impersonation and replay attacks. More secure PPP authentication schemes, such as the Challenge Handshake Authentication Protocol (CHAP) or the Microsoft version of that protocol (MS-CHAP), are preferable. CHAP guards against remote client impersonation by using the user’s password to create an encrypted hash of a challenge string instead of passing the actual password during the authentication process. It protects against replay attacks by using a different, arbitrarily selected challenge string for each authentication attempt.

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To access secured resources on Internet Web sites hosted by Internet Information Services (IIS), be sure that Basic Authentication is disabled on the server and that sensitive documents are located on NTFS volumes with suitable permissions configured.

Remote Desktop Protocol (RDP)

A protocol used by Microsoft Windows NT Server, Terminal Server Edition, and by Windows 2000 Server Terminal Services that lets clients communicate with Terminal Services over a network. Remote Desktop Protocol (RDP) is based on the T.120 protocol of the International Telecommunication Union (ITU), a standard multichannel conferencing protocol that is also used in Microsoft NetMeeting conferencing software. RDP is a multichannel-capable protocol that can use separate virtual channels for carrying serial device communication and presentation data sent from the server and encrypted client mouse and keyboard data sent from the client. RDP supports up to 64,000 separate channels for data transmission and supports multipoint transmission.

NOTE

RDP is sometimes referred to as the Remote Display Protocol. It was formerly known as the T.SHARE protocol.

Remote Network Monitoring (RMON)

An extension of the Simple Network Management Protocol (SNMP) that allows detailed monitoring of network statistics for Ethernet networks. Remote Network Monitoring (RMON) is defined in Request for Comments (RFC) 1757.

RMON lets you monitor network traffic on a remote Ethernet segment from a central location on the network to detect problem conditions such as traffic congestion, dropped packets, and excessive collisions. You can use RMON to set network traffic thresholds that trigger alarms so that you can correct network problems before they occur. Embedded RMON support for Ethernet switches lets network administrators monitor switched Ethernet networks that cannot easily be monitored using traditional packet-sniffing network analyzers.

How It Works

Like SNMP, RMON is implemented as a standard Management Information Base (MIB) on RMON-enabled devices. These RMON-enabled devices include the following:

An RMON probe consists of an SNMP agent for collecting information and communicating it to an SNMP management application, and one or more RMON MIBs defining the network objects to be managed. Typically, an SNMP-manageable device such as a hub or router needs additional software installed on it only to provide RMON functionality and turn it into a probe. Other devices called hosted probes are implemented as add-on hardware modules with built-in processing power and memory.

RMON is usually implemented on only one device or interface per TCP/IP subnet. RMON agent software runs on the port of the router or switch, which monitors and collects Ethernet networking statistics for the attached subnet. These statistics relate to the physical layer (layer 1) and the data-link layer (layer 2) of the Open Systems Interconnection (OSI) reference model for networking. An SNMP management console contacts the RMON agent when it wants to collect the statistics in order to analyze them and present them to the network administrator, or network traffic conditions on the device can trigger the agent to notify the management station of an alarm condition using SNMP traps. RMON agents can also collect and store statistics for monitoring trends in network traffic.

The RMON MIB defined in RFC 1757 contains nine groups of manageable objects (RMON monitoring elements) for various aspects of Ethernet traffic monitoring, totaling 204 objects and 2 events. These groups of objects, usually referred to as the RMON1 groups, are as follows:

NOTE

RFC 1513 extends the original RMON specification by adding a MIB group to RMON called Token Ring, which extends RMON functionality to Token Ring local area networks (LANs) by allowing sampling and collection of statistics specific to this networking environment.

RMON2, defined by RFC 2021, extends the original RMON specification with nine more MIB groups that specify the collection of statistics at the network layer (layer 3) and application layer (layer 7). Network administrators can remotely collect information about the flow of data in client/server applications in an enterprise environment. For example, with RMON2-enabled routers and switches, you can determine which workstations are accessing a specific client/server application on a specific server from a remote SNMP management console. RMON2 includes the original RMON MIB groups and extends them with an additional 268 manageable objects.

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Make sure that your RMON-enabled device or probe supports at least groups 1, 2, 3, and 9 from the previous list. Probes that support only these four groups are said to support mini-RMON. Many network hardware vendors provide RMON-enabled devices that support only mini-RMON because these are generally considered the most useful RMON groups.

See also Simple Network Management Protocol (SNMP)

remote procedure call (RPC)

A message-passing programming technology developed by Sun Microsystems and extended by the Open Software Foundation (OSF) that allows an application to execute procedures and interact with services on a remote computer on the network. Remote procedure calls (RPCs) are the preferred method of enabling client/server processing on the Microsoft Windows 2000 and Windows NT platforms, an Microsoft’s implementation of RPC functionality is compatible with that of other implementations, such as those for the IBM AIX, HP-UX, and Sun Solaris operating systems.

How It Works

You use RPCs to pass messages between components of a distributed application that are located on different computers on a network. While local procedure calls (LPCs) provide a mechanism for enabling different parts of an application located on a single computer to communicate with each other, RPCs involve communication between different computers. RPCs actually use a variety of other interprocess communication (IPC) mechanisms such as named pipes, mailslots, Windows Sockets, and NetBIOS to establish connections between the RPC client and RPC server components on different machines.

The remote procedure call service (RPC service), a component of the Windows NT executive running in kernel mode, is responsible for message-passing between the client and server components of a distributed application, usually a client/server application such as Microsoft Outlook (client part) with Microsoft Exchange Server (server part). On a Windows NT–based network, the server part of a distributed application first registers itself with the RPC Locator service. The client part of the application, which is on the local computer, can then query the RPC Locator service to determine the location of the required server part. A process called the remote procedure stub then packages the client’s function call into a suitable RPC message and sends it to the remote computer using the RPC Run Time process. At the remote machine, a process called the application stub receives the RPC message, unpackages it into a function call, and executes it, returning any resulting values to the client part in a similar fashion. From the viewpoint of the client part of the application, the server part appears to be on the same computer.

Remote Registry service

A Microsoft Windows 95 and Windows 98 service that allows the registry editor and the System Monitor tool to connect to a remote computer running Windows 95 or Windows 98 for remote administration and troubleshooting. This arrangement works only if the following conditions are met:

NOTE

Granting remote administration privileges on a computer running Windows 95 or Windows 98 means that the user has full control over all shared network resources on the machine, including access to the full file system through the hidden administrative share Admin$.

repeater

A networking component that extends a network by boosting the signal so that it can travel farther along the cabling.

How It Works

Digital signals traveling on cables weaken with distance—a phenomenon known as attenuation. A repeater is a form of digital amplifier that works at the physical layer (layer 1) of the Open Systems Interconnection (OSI) reference model for networking to regenerate (amplify) the signal so that it can travel farther. Repeaters also perform other functions such as filtering out noise caused by electromagnetic interference (EMI), reshaping the signal, and correcting timing to remove signal jitter so that the signal can travel farther. Repeaters can also be used to join dissimilar media such as unshielded twisted-pair (UTP) cabling and thinnet, but they cannot be used to join dissimilar network architectures such as Ethernet and Token Ring. Repeaters are an inexpensive way to extend a network.

Repeaters can be used in Ethernet and Token Ring local area networks (LANs) to extend signal transmission to remote nodes and over long fiber-optic cabling runs to connect LANs. Repeaters can also be used in mainframe environments for boosting signals for serial transmission to remote terminals.

Other uses for repeaters include the following:

Repeaters are also used in fiber-optic networks to amplify and regenerate light signals for long-distance cable runs. Repeaters come in various types for different network architectures and data communication technologies.

NOTE

Up to two Class II Ethernet repeaters can be cascaded together to connect remote nodes that are up to 205 meters apart.

TIP

Other than increasing signal strength, repeaters do not filter network traffic in any way. In particular, they do not block broadcasts, so if you connect two Ethernet segments using a repeater, you increase the size of the collision domain, which degrades overall network performance. For this reason, bridges and routers are often preferable to repeaters.

See also hub

replay attack

See remote client impersonation

replica domain controller

A type of domain controller in a Microsoft Windows 2000–based network. A replica domain controller is a domain controller that has joined an existing domain. The replica domain controller gets its copy of the Active Directory database from the first domain controller in the domain. A replica domain controller is created when an existing member server in a domain is promoted to a domain controller using the Active Directory Installation Wizard.

Replica domain controllers can provide several functions in a Windows 2000–based network, including the following:

TIP

You must have administrative privileges in the domain to promote an existing member server to a replica domain controller. At least one Domain Name System (DNS) server must also be running on the network, and at least one domain controller must be running in the target domain.

See also Active Directory, domain controller

replication

See directory replication in Windows 2000

Replicator

A built-in group on all servers and workstations running Microsoft Windows NT. The Replicator group is used by the Directory Replicator Service to replicate part of the file system between computers running Windows NT. The group’s membership is initially empty. When you configure the Directory Replicator Service, you must create a special user account with any name to provide a context in which the service can start up and run. You must make this account a member of the Replicator, Backup Operators, and Domain Users groups. The Replicator group must also have change permission for the Export and Import folders on the computers involved in replication and must be granted the system right called Logon As A Service using User Manager for Domains in order for replication to function properly.

See also Directory Replicator Service

Report Writer

A tool included with Microsoft Site Server and Microsoft Site Server Express that can take Web server log files that have been imported using the Usage Import tool and generate summary or detail reports on several topics, including the following:

Request for Comments (RFC)

A document that describes the standards, protocols, and technologies of the Internet and TCP/IP. Since 1969, about 2400 Requests for Comments (RFCs) have been published on various networking protocols, procedures, applications, and concepts.

Internet and TCP/IP standards are generated by consensus rather than by committee. Any member of the Internet Society (ISOC) can submit an RFC for consideration, although submission is usually done through the Internet Engineering Task Force (IETF). Once published, an RFC is reviewed by various technical groups and given one of five classifications:

Once an RFC is classified, it is published as an Internet Draft and is discussed and tested by research and technical groups and individuals. It might eventually go through the following stages of development:

  1. Proposed standard: Stable, well understood, and generally considered useful

  2. Draft standard: Stable enough to develop implementations of the standard in applications and networking technology

  3. Internet standard: Technically mature, widely implemented, and significantly beneficial to the Internet community

RFCs are sequentially numbered and published by the RFC Editor at the Information Sciences Institute at the University of Southern California.

NOTE

Old RFCs are not updated, so several RFCs might relate to the same Internet protocol or technology, and some of them might be obsolete. To find the current RFC for a protocol or technology, see the Internet Architecture Board (IAB) Official Protocol Standard published quarterly by the IAB. The following table shows some of the important RFCs for commonly used Internet protocols.

Some Important RFCs for Internet Protocols

Protocol RFC(s)

ARP

826

DHCP

2131, 2132

DNS

1034, 1035

FTP

959

HTTP-1.1

2068

ICMP

792

IGMP

1112

IMAP4

2060

IP

791, 919, 922, 950

IPv6

1883

Kerberos

1510

LDAPv3

2251

MIME

2045, 2046, 2047, 2049

NetBIOS

1001, 1002

NNTP

977

OSPFv2

2328

POP3

1939

PPP

1661, 1662

PPP-CHAP

1994

PPP-MP

1990

RADIUS

2138

RMON

1757

RSVP

2205

SMTP

821, 822, 974, 1869, 1870

SNMP

1157

SNMPv2

1441

TCP

793

Telnet

854, 855

UDP

768

On the Web

•

RFC Editor : http://www.rfc-editor.org

reservation

An IP address that is reserved for a specific computer by a Dynamic Host Configuration Protocol (DHCP) server. The reservation contains the IP address to be leased and the MAC address of the computer it will be leased to. Reservations are often used for servers on a network, which normally should all have the same IP address. An alternative procedure is to manually assign these servers a static IP address. The advantage of using a reservation is that the IP address of the server is centrally managed in the database of the DHCP server, which means there is less chance of an address conflict.

Reservations (or static IP addresses) are always recommended for

TIP

To create a reservation for a computer, you must know the MAC address of its interface. On computers running Microsoft Windows NT or Windows 2000, you can enter ipconfig at the command prompt to determine this value; on computers running Windows 95 or Windows 98, you can enter winipcfg in the Run dialog box (which you access via the Start menu).

resolver

Abstractly, a client in the Domain Name System (DNS). More concretely, a resolver is software running on a TCP/IP host that enables the host to query a name server in order to resolve a host name into its associated IP address. The resolver software enables the host to formulate and send a query to the name server, interpret the response from the name server, and pass this information to the program that initially called the resolver software.

On UNIX platforms with BIND implemented, a resolver is a set of library routines that are linked to the client programs that need to use them, such as Web browsers or File Transfer Protocol (FTP) client programs. Computers running Microsoft Windows become resolvers when you install the TCP/IP protocol stack and configure the IP address of a DNS server on the DNS tab of the TCP/IP property sheet.

See also Domain Name System (DNS), host name resolution

resource domain

In Microsoft Windows NT, a type of domain in an enterprise networking environment that includes file, print, and other resources for users throughout the enterprise. Resource domains are part of a master domain model or multiple master domain model enterprise-level implementation of Windows NT. Resource domains simplify resource administration by separating the administration of resources from the administration of user accounts.

How It Works

In a master domain model implementation of Windows NT, an account domain—or master domain—contains user accounts for every user in the enterprise and is usually located at corporate headquarters. Servers and workstations at branch offices belong to other domains called resource domains. A trust relationship is established so that each resource domain in the enterprise trusts the account domain. Users at branch offices who want to log on to the network simply log on to the account domain even though their workstations are located within resource domains. Administrators at branch offices are responsible for managing only the resources (file and print shares, Web servers, database servers, and so forth) for their own domain and are not involved in account management.

See also account domain, trust relationship

resource for a cluster

Any physical or logical component that can provide a service to a network client and that can be taken offline and brought online by Microsoft Cluster Server (MSCS) or Windows Clustering. Resources are physical or logical entities that are managed by a node of a cluster. MSCS supports a number of types of resources, which you can manage using the Cluster Administrator program. These resource types include the following:

Related MSCS terminology with regard to resources includes the following:

NOTE

MSCS resources always exist in one of the following states:

resource on a network

Any files, applications, or devices on a network that users need access to. Examples of network resources include the following:

resource record

An individual entry in a Domain Name System (DNS) database that contains information about domain names in the DNS.

How It Works

Resource records are individual records (lines) in a text file called a zone file, which is located on a DNS server. You can edit this zone file with a simple text editor, but Microsoft Windows NT and Windows 2000 platforms offer a GUI-based administrative tool that simplifies the creation and management of resource records on a Windows NT or Windows 2000 DNS server. A typical resource record consists of a series of fields separated by spaces.

The most common type of resource record is the address record, or A record, which maps the IP address of a TCP/IP to its DNS name. Other common types of resource records include CNAME, NS, PTR, SOA, and SRV. The following table describes some important types of resource records that you can create in the standard implementation of DNS as defined by Request for Comments (RFC) 1035 and later.

Possible DNS Resource Records

Record Type Description

A (address)

Maps the IP address to the host name

CNAME (canonical name)

Creates an alias for a host name

HINFO (host information)

Specifies information about the host, such as operating system and CPU type

MX (mail exchanger)

Indicates a Simple Mail Transfer Protocol (SMTP) host (mail forwarder)

NS (name server)

Indicates a DNS name server that is authoritative for the domain

PTR (pointer)

Points to another location in the DNS namespace

SOA (start of authority)

Indicates the name server that is authoritative for the domain

SRV (server)

Locates a host that can provide a specific network service

See also Domain Name System (DNS)

reverse hosting

Also called virtual hosting, an extension to reverse proxying that is supported by Microsoft Proxy Server. Using reverse hosting, the proxy server simulates virtual roots on a Web server and redirects requests for a particular domain and root combination to a single Web server. This approach means that only one hole needs to be opened through the Proxy Server firewall to allow Hypertext Transfer Protocol (HTTP) requests to enter. Reverse proxying works as an application layer proxy service and supports HTTP only.

reverse name lookup

The process of a resolver querying a name server to resolve a host’s IP address into its associated fully qualified domain name (FQDN). This is the reverse of the usual host name resolution process, in which a resolver queries a name server to resolve a host name into its associated IP address. Reverse name lookups use a special domain called in-addr.arpa.

Reverse name lookups are used in a variety of circumstances. For example, when a Web browser contacts a Web server, the Web server obtains the IP address of the computer the browser is running on. The Web server software often uses a reverse lookup to try to resolve the client’s IP address into its associated FQDN, usually for purposes of logging the Hypertext Transfer Protocol (HTTP) session.

See also name lookup

reverse proxy

A service or server that offloads Web publishing responsibilities from Web servers and allows you to securely connect a company’s internal Web servers to the Internet or to the rest of the company intranet. In reverse proxying, a proxy server is used to impersonate a Web server to the outside world. The proxy server receives client requests for Web content and fulfills these requests from its cache. It forwards client requests to the actual Web server only if it cannot serve the requests from its own cache.

Microsoft Proxy Server supports reverse proxying so that you can publish to the Internet without compromising your internal network’s security. Proxy Server uses reverse proxying to send client requests downstream to a Web server or group of Web servers that are located behind the proxy server. This configuration results in improved Web server capacity planning, protects the security of data while allowing access to the Internet, and allows Web servers to access other servers on the internal network for publishing purposes.

rexec

A TCP/IP utility that enables clients to run commands directly on remote hosts. The remote host must be running the rexec service or daemon for the execution to work. Rexec authenticates the username on the remote host before executing the command and prompts the client to enter a password. Rexec is one of the r-commands available on all UNIX systems.

NOTE

Microsoft’s implementation of TCP/IP on Windows NT and Windows 2000 includes rexec client software but no rexec service. Rexec provides functionality similar to that of rsh, except rexec uses clear-text password authentication.

TIP

You cannot use rexec to run interactive commands such as vi or emacs. Instead, use Telnet to run interactive commands on a remote host. Note also that rexec forwards the user’s password as clear text, which can pose a security risk in some environments.

RFC

See Request for Comments (RFC)

RG

Stands for Radio Guide, a U.S. Army specification for grades of transmission lines. RG specifications refer to forms of coaxial cable used in networking, as in the following examples:

rights

Also known as system rights, the system tasks that a user can perform on a Microsoft Windows NT workstation, on a server running Windows 2000 or Windows NT, or on a domain. These tasks include changing a server’s clock, rebooting the machine, logging on to the local console, and performing a backup. A system administrator can view and modify Windows NT rights by using the Policies menu in User Manager for Domains. Windows NT built-in groups have predefined sets of rights assigned to them. The following table lists the basic Windows NT rights and the users and groups that have them by default.

Windows NT Rights

Right Users and Groups Who Have the Right by Default

Access this computer from the network

Administrators

Everyone

Add workstations to the domain

Administrators

Back up files and directories

Administrators

Backup Operators

Server Operators

Change the system time

Administrators

Server Operators

Force shutdown from a remote system

Administrators

Server Operators

Load and unload device drivers

Administrators

Log on locally

Administrators

Account Operators

Backup Operators

Print Operators

Server Operators

Manage the auditing and security log

Administrators

Restore files and directories

Administrators

Backup Operators

Server Operators

Shut down the system

Administrators

Account Operators

Backup Operators

Print Operators

Server Operators

Take ownership of files and other objects

Administrators

NOTE

In Microsoft Exchange Server, rights are individual permissions that can be assigned to users and groups to control their level of access to objects in the Exchange directory hierarchy.

See also Exchange permissions, permissions

ring topology

A networking topology in which network stations are connected along a single path whose ends are joined to form a circle. The circle might be logical only; the physical arrangement of the cabling might be starlike, with a hub or concentrator at the center. A ring network is based on a ring topology.

The ring topology is commonly used in the following kinds of networks:

graphic r-7. ring topology.

Graphic R-7. Ring topology.

See also bus topology, mesh topology, star bus topology, star topology

RIP

See Routing Information Protocol (RIP)

RIPE

See American Registry for Internet Numbers (ARIN)

RJ connectors

A family of push-and-click connectors for twisted-pair wiring in telephone and network wiring. RJ stands for Registered Jack. RJ types define both a jack or receptacle (female) and a plug (male) type of connector. The most common types of RJ connectors are as follows:

NOTE

The diagram shows RJ-11 and RJ-45/48 connectors, which are used to terminate both ends of UTP cabling. Pins are labeled 1 through 4 or 1 through 6 for 4-wire and 6-wire RJ-11, and 1 through 8 for 8-wire (four-pair) RJ-45/48. Cables can be straight-pinned or cross-pinned, depending on their use. For example, a straight-pinned RJ-45-terminated UTP cable is used to connect a computer to a 10BaseT hub, while a cross-pinned cable or crossover cable is used to connect two computers directly or to connect two hubs.

graphic r-8. rj connectors.

Graphic R-8. RJ connectors.

The following table shows the pinning for these various cables, with the colored wires coded as follows:

If these colors are combined in striped cables, the coloring is coded OR/W for orange/white or orange with white striping, and so on. RJ-11 and RJ-45 cables generally use solid-color wires, while RJ-48 cables are usually striped. Note that RJ-45 has two types of cross-pinning: 568A/B and USOC. If the pinning of a wire is listed as Y (1–4), it means that the yellow wire is connected to pin 1 at one end and to pin 4 at the other.

Types of Cable Pinning

Connector/Cable Pinning

RJ-11 straight (4-wire)

Y (1-1), G (2-2), R (3-3), BL (4-4)

RJ-11 crossed (4-wire)

Y (1-4), G (2-3), R (3-2), BL (4-1)

RJ-11 straight (6-wire)

BL (1-1), Y (2-2), G (3-3), R (4-4), BK (5-5), W (6-6)

RJ-11 crossed (6-wire)

BL (1-6), Y (2-5), G (3-4), R (4-3), BK (5-2), W (6-1)

RJ-45 straight (8-wire)

BL (1-1), OR (2-2), BK (3-3), R (4-4), G (5-5), Y (6-6), BN (7-7), S (8-8)

RJ-45 USOC crossed (8-wire)

BL (1-8), OR (2-7), BK (3-6), R (4-5), G (5-4), Y (6-3), BN (7-2), S (8-1)

RJ-45 568A/B crossed (8-wire)

BL (1-3), OR (2-6), BK (3-1), R (4-5), G (5-4), Y (6-2), BN (7-8), S (8-7)

RJ-48C straight (8-wire)

OR/W (1-1), W/OR (2-2), (3-3) unused, BL/W (4-4), W/BL (5-5), (6-6) unused, BL drain (7-7), OR drain (8-8)

RJ-48C crossed (8-wire)

OR/W (1-4), W/OR (2-5), (3-3) unused, BL/W (4-1), W/BL (5-2), (6-6) unused, BL drain (7-7), OR drain (8-8)

RMON

See Remote Network Monitoring (RMON)

RMON2

See Remote Network Monitoring (RMON)

roaming user profile

A Microsoft Windows NT or Windows 2000 user profile that is stored on a network server so that the user can access personal desktop settings from any machine on the network. Roaming user profiles are generally created for users by the system administrator. A roaming profile that cannot be modified by the user is called a mandatory user profile. If the server on which the profile is stored is unavailable when the user logs on to the network, the locally cached copy of the profile stored on his or her workstation will be used instead.

How It Works

There is no default location for roaming profiles on a Windows NT–based or Windows 2000–based network. They can be stored either on domain controllers or on member servers. To create a network share for users’ roaming profiles, create and share a folder called Profiles on one of the servers. Then proceed as follows:

NOTE

Windows 95 and Windows 98 also support roaming user profiles, but Windows NT user profiles are not compatible with Windows 95 and Windows 98 user profiles. If a user has a Windows NT roaming profile configured, that user’s desktop settings are available from computers running Windows NT Workstation but not from machines running Windows 95 and Windows 98.

See also local user profile, mandatory user profile, user profile

roles

In Microsoft Exchange Server, groups of Exchange rights that can be assigned to users and groups to control their level of access to objects in the Exchange directory hierarchy. Exchange has a number of predefined roles for assigning common sets of permissions to users and groups, as shown in the following table.

Exchange Rights

Right Role

Admin

Permissions Admin

Service Account Admin

View Only Admin

User

Send As

Search

Add child

x

x

x

Modify user attributes

x

x

x

x

x

Modify admin attributes

x

x

x

Delete

x

x

x

Logon

x

x

x

x

Modify permission

x

x

Replication

x

Mailbox owner

x

x

Send as

x

x

x

Search

x

Administrators can also create custom roles to grant special types of access to the directory.

See also Exchange permissions

root

The base of a hierarchical file system. The root directory contains the tree of directories and files that make up the file system. The symbol used to represent this directory depends on whether the file system is on a Microsoft Windows platform or a UNIX platform. Windows designates the root with a backslash (\), and UNIX uses a forward slash (/). The root directory is the first element in the absolute path of a file or directory on the file system.

NOTE

The term “root” can also refer to the user with the highest level of administrative rights, especially on a UNIX system. Other names for this user are SuperUser (UNIX), Supervisor (NetWare), and Administrator (Windows NT).

The term “root” can also refer to the highest-level entity in a directory system structure. For example, the root of Active Directory in Windows 2000 is the RootDSE object.

root certificate

A digital certificate that attests to the identity of a certificate authority (CA). A root certificate is signed by the CA itself (self-signed) or by a higher authority in a hierarchy of CAs in a public key infrastructure (PKI). Every CA requires a root certificate so that it can be “trusted” by entities that request digital certificates from it. If a client trusts the root certificate of a CA, it automatically trusts any other certificates that are issued by that CA. Root certificates thus form one of the foundations of public key cryptography.

Microsoft Certificate Server, which is included with Microsoft Windows NT Option Pack, and Certificate Services in Windows 2000 can self-sign a root certificate during the installation process or create a certificate request file that can be used to request a certificate from a higher CA.

root domain

A domain in a domain tree of a Microsoft Windows 2000–based network that is the highest-level parent domain in the tree. All other domains in the tree derive their Domain Name System (DNS) name from the root domain and form a contiguous namespace with the root domain. An example of a root domain name for a company called Expedia might be expedia.com. The root domain is the first domain you create when you implement Active Directory in an enterprise. All other domains you create derive their DNS name from the root domain.

TIP

You should select a root domain name before you implement Active Directory on your Windows 2000–based network. The name should be easily recognized by users in the outside world, and you should make sure that it is legally acceptable and does not violate existing trademarks or duplicate registered company names. Root domain names should be static and not subject to change.

If you plan to connect your network directly to the Internet, you should register your root domain name with the Internet Network Information Center (InterNIC) or some other domain name registration authority. You can use separate external and internal root domain names in your enterprise network if you want to separate network resources that will be accessible to outside users on the Internet from those intended for internal company use only. You should register both the internal and external root domain names to prevent future naming conflicts. You should also use a firewall to protect the private domain from the Internet.

graphic r-9. root domain.

Graphic R-9. Root domain.

See also Active Directory, domain tree

RootDSE

The object that resides at the top of the directory hierarchy in Active Directory in Microsoft Windows 2000. RootDSE is the root of the logical namespace for Active Directory and is the top of the search tree for accessing Active Directory using the Lightweight Directory Access Protocol (LDAP). The RootDSE object is specified in Request for Comments (RFC) 1777.

How It Works

The RootDSE object is located in the Directory System Agent (DSA) within the directory service module ntdsa.dll, which is part of the security subsystem in Windows 2000. The RootDSE object is a container object and has a Configuration container that is used to store configuration information for the enterprise network. The Configuration container contains the various naming contexts for Active Directory. (A naming context is a contiguous subtree of Active Directory and forms a unit of information for replication purposes.) These naming contexts include the following:

TIP

You can view the RootDSE object by using the Active Directory Object Browser. Choose Run from the Start menu, type adsvw to start the Object Browser, and then enter the following LDAP Uniform Resource Locator (URL):

 LDAP://RootDSE

routable protocol

Also called a routed protocol, a network protocol that supports routing of packets on an internetwork using their logical network layer (layer 3) addresses. The most commonly used routable network protocols are as follows:

Common network protocols that are not routable include the following:

route

Generally, a specific path along which packets can be forwarded on an internetwork by a router. Specifically, a TCP/IP utility for viewing and modifying the internal routing table on a computer running Microsoft Windows 2000, Windows NT, Windows 98, or Windows 95. This internal routing table contains routing information that determines how the computer delivers packets to local and remote hosts on the network. If a multihomed server running Windows 2000 or Windows NT is used, you can use the route command to configure the routing table for static routing. (In Windows 2000, you can also use Routing and Remote Access to configure static routing.)

Example

Typing route print at the command prompt displays the routing table of the local computer. Typing route add 172.16.25.0 mask 255.255.255.0 172.16.10.1 metric 2 adds a new route to the routing table, specifies that any packets destined for the network with network ID 172.16.25.0 should be forwarded to the router interface 172.16.10.1 in the local network, and specifies that packets sent along this route will traverse two hops on the network.

router

A networking device that is used to extend or segment networks by forwarding packets from one logical network to another. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines.

How It Works

Routers work at the network layer (layer 3) of the Open Systems Interconnection (OSI) reference model for networking to move packets between networks using their logical addresses (which, in the case of TCP/IP, are the IP addresses of destination hosts on the network). Because routers operate at a higher OSI level than bridges do, they have better packet-routing and filtering capabilities and greater processing power, which results in routers costing more than bridges.

Routers contain internal tables of information called routing tables that keep track of all known network addresses and possible paths throughout the internetwork, along with the cost of reaching each network. Routers route packets based on the available paths and their costs, thus taking advantage of redundant paths that can exist in a mesh topology network. Because routers use destination network addresses of packets, they work only if the configured network protocol is a routable protocol such as TCP/IP or IPX/SPX. This is different from bridges, which are protocol independent.

graphic r-10. typical uses for routers.

Graphic R-10. Typical uses for routers.

Routers are classified as one of the following:

Routers are used to segment large networks and join LANs to wide area networks (WANs), and they form the basis of the public packet-switched TCP/IP network known as the Internet. Routers can be so complex that Cisco Systems, the major vendor of enterprise-level routers, has an operating system for routers called Internetwork Operating System (IOS) that is devoted solely to managing routers.

NOTE

Routers generally block broadcast traffic and can thus prevent broadcast storms from slowing down the flow of traffic in a network. Routers can also be used to join dissimilar media such as unshielded twisted-pair (UTP) cabling and fiber-optic cabling, and different network architectures such as Token Ring and Ethernet.

TIP

Routers often provide basic firewall functions by filtering out packets based on their source or destination network address. Such a device is known as a packet-filtering router.

TIP

To use a router to connect a LAN to the Internet over a high-speed T1 line, connect a router to the main hub or switch in the LAN, and then connect the serial port on the router to a Channel Service Unit/Data Service Unit (CSU/DSU), which connects to a dedicated T1 line. Your telco will provide Internet access through the T1 line.

Routers are similar to bridges in that they both forward packets and can be used to either segment or join networks. However, routers also use network layer (layer 3) addresses such as IP addresses to forward packets, while bridges use layer 2 (or MAC) addresses. When should you use a bridge and when should you use a router? You should use bridges to connect network segments that run the same network protocol—for example, to connect an Internet Protocol (IP) segment to an IP segment. You must also use bridges when you run nonroutable network protocols such as NetBEUI on your network. On the other hand, you should use routers to connect network segments that run different network protocols—for example, to connect an IP segment to an Internetwork Packet Exchange (IPX) segment. And generally speaking, routers are more intelligent than bridges and improve network bandwidth by not forwarding broadcast packets to other networks. Finally, when you use TCP/IP to connect to the Internet, use routers unless you absolutely need to use a bridge.

See also routing

routing

The process of selecting a path through an internetwork over which to transmit packets to a destination host or hosts and then having devices called routers forward the packets to those hosts. For routing to occur, a routable protocol such as TCP/IP or IPX/SPX must be used.

How It Works

Routing takes place at the network layer (layer 3) of the Open Systems Interconnection (OSI) reference model. On a TCP/IP internetwork, this means that routing involves delivering packets to destination IP addresses on the internetwork.

The first and main part of the routing process consists of determining the path over which packets will travel from the sending, or original, host to the receiving, or destination, host. The second part of the process involves having routers switch packets from one successive segment, or “hop,” of the path to the next until the packets arrive at their destination.

Routers are devices that join subnets, which are separate and distinct networks that make up an internetwork. The routers maintain internal tables called routing tables, which contain information describing the potential paths that data can take to travel through the internetwork. Between any two subnets on the internetwork, there can be more than one path or route by which packets can travel. The routing information stored in the routing tables describes the metric or cost value for each possible route between different subnets. When packets need to be sent to a host or hosts on another network, they are forwarded to a router that is connected to the local network, which then checks its routing tables to determine which path the packets should take. Packets are usually sent along the path with the lowest cost value or metric. If two paths to the same destination have the same metric, packets can be load-balanced between the two routes.

The value of the metric for a specific path depends on several factors. For example, the metric might be proportional to the number of routers that the packet stream must be switched through (the number of hops traversed) in order to reach the end of the path. The metric might also depend on other factors such as the delay or latency of packets when they are processed by each router, the amount of traffic congestion (load) at the router, available bandwidth, and the relative reliability of the routers. Network administrators can manually specify metrics for each path and enter them into routing tables by using static routers, or they can use dynamic routers, which use a routing algorithm to automatically calculate metrics for each possible path. Dynamic routers automatically calculate metrics by communicating with each other using special protocols called routing protocols. Examples of routing protocols include Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) Protocol.

Once the routing table of a router has been configured (or once the tables of all dynamic routers have “converged” and stabilized), the router carries out its switching function. This switching function is essentially independent of the particular routing protocol being used. It works like this: If a host on the local network needs to send a packet to a host on a remote network, it checks its own internal routing table to determine which router to contact and then uses Address Resolution Protocol (ARP) to obtain the MAC address of the local router interface that connects the local network to the remote network. The host then sends the packet directly to the local router interface. The network layer header of the packet contains the logical network address (the IP address on a TCP/IP internetwork) of the destination host that the packet needs to be delivered to. The router receives the packet, inspects the network-layer destination address in the packet’s header, and compares the address to the route information stored in the router’s internal routing table in order to determine what to do with the packet. If the router cannot determine what to do with the packet, it simply drops the packet. Otherwise, it forwards the packet to another router, which forwards it again until the packet finally reaches its destination network. As the packet is switched from router to router, its network layer destination address remains the same, but its MAC address keeps changing to that of the next router interface along the path.

NOTE

Although routing is normally considered the exclusive job of routers, routing actually occurs in two places on a network such as a TCP/IP internetwork:

Routing in a network can suffer from a number of problems. One problem is the existence of routing loops, which occur when a packet passes through the same router more than once on a given trip. The result is that the packet loops until its lifetime decreases to zero and a router discards it. The originating host usually never knows that the packet was dropped and did not reach its destination. Routing loops occur most often in networks that use incorrectly configured static routers. Routing algorithms for dynamic routers can usually detect loops and reconfigure routing tables to eliminate them.

Another problem is convergence. In a large internetwork using dynamic routers, it might take some time for a change in one router’s tables to propagate to all other routers in the internetwork. In the meantime, temporary routing loops can occur and less efficient network paths might be chosen, resulting in more traffic congestion.

TIP

To view the internal routing table of a computer running Microsoft Windows 2000 or Windows NT, type route print at the command prompt.

See also router

routing algorithm

A mathematical procedure that a dynamic router uses to calculate entries for its routing table.

How It Works

Routing algorithms are implemented as software running within the internal CPU of a router. They are implemented as a routing protocol because they involve procedures and protocols that allow routers to exchange information with one another in order to calculate the metrics of various paths or routes through an internetwork. Routing algorithms base their work off the values contained in a combination of variables. These values can be determined dynamically by inspecting header information in packets directed toward the router, or they can be manually specified by network administrators. The routing algorithm then processes the values of these variables to generate the internal routing table for the router. The variables are generally known as routing metrics and can include the following:

Routing algorithms are usually implemented as a combination of dynamic (real-time calculated) and static (specified by the network administrator) factors. Algorithms are usually implemented in a distributed fashion, with each router independently calculating its own routing tables, and in the case of dynamic routers, exchanging routing information with each other as well. This provides a degree of fault tolerance for the routing network: If one router goes down, all other routers can reconfigure their routing tables to route traffic around the failed router. When the failed router is restored, the routing tables are recalculated. Some routing algorithms support forwarding packets over several paths to a given destination (when such multiple paths exist). They can thus better manage network traffic by load balancing packets accordingly.

One major distinction between routing algorithms involves the space within which they operate. In a flat routing space, all routers are peers, while in a hierarchical routing space, different routing domains, areas, or autonomous systems are connected using a backbone routing network. The advantage of a hierarchical routing space is that it reduces the amount of intercommunication traffic that must take place between routers in order for them to calculate their routing tables. For example, routers that forward traffic only within their own routing table do not need to exchange routing information with routers in other domains. The downside, of course, is that a hierarchical system is much more difficult to implement and maintain than a flat routing space.

From a mathematical point of view, routing algorithms come in two common types: link state routing algorithms and distance vector routing algorithms. A link state routing algorithm is a hierarchical routing space algorithm that forms the basis of the Open Shortest Path First (OSPF) Protocol, while a distance vector routing algorithm is a flat routing space algorithm that forms the basis of the Routing Information Protocol (RIP). From a network administrator’s perspective, the differences between these algorithms are as follows:

See also routing, routing protocol

Routing and Remote Access

An integrated component of Microsoft Windows 2000 that provides both remote access and routing capabilities. Routing and Remote Access supports both dial-up and virtual private network (VPN) remote access clients, and supports routing of Internet Protocol (IP), Internetwork Packet Exchange (IPX), and AppleTalk. Using this component, a server running Windows 2000 Server can function as a Remote Access Service (RAS) server, a VPN server, or even a branch-office router. Routing and Remote Access is also the name of the Microsoft Management Console (MMC) snap-in that is used to manage these services in Windows 2000.

How It Works

The Routing and Remote Access snap-in is used to configure the server side of remote access on servers running Windows 2000 and to configure routing on servers running Windows 2000 with multiple local area network (LAN) or wide area network (WAN) interfaces.

When you use the snap-in to install and configure remote access you create a remote access server that provides these two types of connectivity: dial-up networking and virtual private networking.

Some of the new remote access features supported by Windows 2000 include the following:

Routing and Remote Access in Windows 2000 provides powerful industry-standard routing capabilities that can turn a computer running Windows 2000 Server into a full-featured, enterprise-class router for both LAN and WAN internetworks. A computer running Windows 2000 Server that has the Routing and Remote Access service installed and configured on it is usually referred to as a Windows 2000 router. Supported features include the following:

NOTE

The client side of remote access on Windows 2000 Professional clients is configured using the Network Connection Wizard, which provides a step-by-step method for creating and configuring basic inbound and outbound connections.

Routing and Remote Access Service (RRAS)

An add-on for Microsoft Windows NT Server version 4 with Service Pack 3 or later that provides additional support for TCP/IP internetworking, including the following:

NOTE

Routing and Remote Access Service (RRAS) replaces the existing Remote Access Service (RAS) on Windows NT 4 and fully supports the existing capabilities of RAS. For information on RRAS for Windows 2000, see the entry on Routing and Remote Access elsewhere in this chapter.

Routing Information Protocol (RIP)

A routing protocol that is used to exchange routing information between dynamic routers on Internet Protocol (IP) or Internetwork Packet Exchange (IPX) internetworks. Routing Information Protocol (RIP) was designed in 1980 to be used with the Xerox Network Systems (XNS) protocol suite but is most commonly used today in small to mid-sized TCP/IP internetworks. RIP first became popular as a result of its inclusion in release 4.2 of the Berkeley BSD UNIX platform. It is supported by Microsoft Windows NT Server and Microsoft Windows 2000 Server and has been adapted to the AppleTalk networking system as the Routing Table Maintenance Protocol (RTMP).

How It Works

RIP is based on the distance vector routing algorithm, one of several common routing algorithms that routers use to dynamically calculate the cost or metric of each possible path through an internetwork. RIP has been implemented for both TCP/IP and IPX/SPX internetworks as RIP for IP and RIP for IPX, respectively. RIP is designed for intradomain routing (routing within a flat routing space or routing domain).

Routing tables in RIP-enabled routers are calculated on the basis of the number of hops to the destination network. RIP routers do not use other routing metrics such as load, bandwidth, latency, or Maximum Transmission Unit (MTU) in calculating routing costs. The routing table of a RIP router contains the cost in hops of every path to every destination network in the internetwork.

RIP-enabled routers on a TCP/IP internetwork broadcast their complete routing tables every 30 seconds over User Datagram Protocol (UDP) port 520 using RIP advertisements. You might assume that this adds a lot of overhead to network traffic, but this information is broadcast information and is thus propagated only throughout the local network and received only by routers that have a routing interface to the local network. RIP does not support multipath routing. If a routing table has multiple routes for a single network ID, RIP stores the route with the lowest metric (number of hops to destination).

When a RIP router is first turned on, it announces its presence using a General RIP Request message so that neighboring RIP routers can send it advertisements of their routing tables. These RIP advertisements from neighboring RIP routers allow the router to build its own routing tables. In addition, the new RIP router announces to its neighbors all network IDs of locally attached networks so that they can update their routing tables with this information.

RIP supports a maximum metric of 15; networks that are more than 15 hops away are unreachable using RIP. This limits RIP implementation to small and mid-sized internetworks. RIP metrics are independent of TCP/IP Time to Live (TTL) values, so if two networks are separated by more than 15 routers on a RIP-enabled internetwork, packets sent between them are dropped even if their TTL values have not decremented to zero. If you try to send a packet to a network more than 15 hops away, a RIP router returns an Internet Control Message Protocol (ICMP) Destination Unreachable message.

RIP is a well-supported industry standard routing protocol. Its main disadvantage is that the routing table of a RIP-enabled router can be quite large because it contains all possible routes to all possible networks. RIP advertisement packets are only 512 bytes in length and can contain a maximum of 25 different routing table entries, so a large routing table with hundreds of entries means that dozens of RIP packets are broadcast every 30 seconds. This can result in a lot of extra broadcast traffic on the local subnet. RIP is therefore not suitable for large internetworks or for networks with many slow wide area network (WAN) links. RIP announcements are not synchronized over the internetwork and are sent without expectation of acknowledgments. This can lead to convergence problems and routing loops.

In addition, routing entries in a RIP routing table time out 3 minutes after the last RIP announcement is received, so if a RIP router goes down, it takes time for this information to propagate throughout the internetwork, a problem known as slow convergence. This 3-minute timeout value exists so that information about routers that unexpectedly fail or go down can be propagated throughout the internetwork. If neighboring routers do not hear from a RIP router within 3 minutes, networks that are locally attached to the missing router are assigned a hop count of 16, making them unreachable.

NOTE

Microsoft Windows NT supports RIP for both TCP/IP (RIP for IP) and NWLink IPX/SPX-Compatible Transport (RIP for IPX). There are two versions of RIP:

A RIP-enabled router that can receive RIP broadcasts but cannot send them is called a Silent RIP Router.

TIP

Another disadvantage of RIP is that it cannot take into account real-time network parameters such as congestion, latency, or router load when the RIP router determines whether to forward a packet along a specific route. Use the Open Shortest Path First (OSPF) Protocol if you want to dynamically take into account such real-time network parameters, but be aware that implementing OSPF is fairly complex and might require you to upgrade your existing routers.

If your RIP-enabled internetwork includes slower WAN links as well as fast local area network (LAN) links between networks, you can assign the WAN links hop values that are greater than 1 to compensate for their slower speed. For example, you can assign a T1 link between two networks a hop count of 3 or 4. However, the total hop count between any two networks must still be less than or equal to 15, and such a configuration makes sense only if the topology of the network is a complex mesh involving both fast LAN and slow WAN links.

RIP routers should be turned off properly so that they can advertise the fact that they are being turned off to their neighboring routers. This notification, called a triggered update, declares all locally attached networks to the router as having a hop count of 16, making them unreachable. These triggered changes then propagate throughout the internetwork.

See also routing, routing algorithm

routing interface

In general, the port at which a router connects to a given network. For a given network, the port on the router that is directly connected to the network is called a local router interface, while any port on the router that is connected to a different network is called a remote router interface. Each interface of a router has a unique MAC address, just like a network interface card (NIC) in a computer.

In the Routing and Remote Access Service (RRAS) of Microsoft Windows 2000, a router interface is a physical or logical interface over which packets are forwarded. These packets can be unicast packets of Internet Protocol (IP), Internetwork Packet Exchange (IPX), or AppleTalk, or multicast packets of IP. Routing interfaces in Windows 2000 RRAS can be

NOTE

If only one router is connected to a network, the local router interface is the default gateway for all hosts on that network. Windows 2000 and Windows NT support configuring additional gateways by using the Advanced button on the TCP/IP property sheet.

routing metric

A variable or factor that a dynamic router can use to calculate its routing table to determine which path or route the router should use to forward a packet.

How It Works

Routing metrics enable routers to make intelligent decisions about how to forward packets to ensure that

The simplest metric used by routers to calculate routing table entries is the number of hops to a given destination network. For example, this metric is used by the Routing Information Protocol (RIP), which allows dynamic routers to communicate with each other to share routing information and synchronize the entries of their routing tables. If you need more control over the paths that packets take, you can use protocols such as Open Shortest Path First (OSPF) Protocol and Interior Gateway Protocol (IGP), which can use a number of other metrics, including real-time metrics that routers determine dynamically, such as the following:

Other routing metrics are manually entered into the router configuration by network administrators who have a knowledge of the physical layout and performance of the network. Such metrics can include the following:

See also routing

routing protocol

A protocol that enables the exchange of routing tables between routers in an internetwork. Routing protocols are the software implementation of specific routing algorithms, which are mathematical procedures for determining the cost of various paths or routes through an internetwork so that traffic can be routed most efficiently.

Routing protocols are generally implemented in medium to large-sized TCP/IP internetworks to simplify the administration of routing tables. Common routing protocols include the following:

NOTE

Dynamic routers talk to each other using routing protocols and are essentially self-configuring (except for the first one installed in an internetwork). Static routers do not talk to each other and must be configured independently.

TIP

Remember that a routing protocol is different from a routable protocol. A routing protocol is used by routers to communicate with each other. A routable protocol, on the other hand, is a network protocol such as TCP/IP or IPX/SPX that can be routed between networks within an internetwork.

See also routing, routing algorithm

routing table

An internal table that a computer or router uses to determine which router interface to send packets to, based on their destination network addresses. Microsoft Windows platforms automatically build their own routing tables, which are used to determine whether to forward specific packets to

To view the internal TCP/IP routing table on a computer running Windows 2000, Windows NT, Windows 98, or Windows 95, type route print at the command prompt.

A typical routing table looks like the following:

 Active Routes: Network Address   Netmask     Gateway Address     Interface  Metric 127.0.0.0       255.0.0.0        127.0.0.1        127.0.0.1    1 172.16.8.0      255.255.255.0    172.16.8.50      172.16.8.50  1 172.16.8.50     255.255.255.255  127.0.0.1        127.0.0.1    1 172.16.255.255  255.255.255.255  172.16.8.50      172.16.8.50  1 224.0.0.0       224.0.0.0        172.16.8.50      172.16.8.50  1 255.255.255.255 255.255.255.255  172.16.8.50      172.16.8.50  1

This computer has a single network interface card (NIC) with the address 172.16.8.50. The columns of this table are as follows:

NOTE

In Microsoft Exchange Server, the routing table is the internal table that defines how messages can be routed to other sites in the Exchange organization and to foreign mail systems through installed connectors and gateways. This routing table is generally known as the Gateway Address Routing Table (GWART).

RPC

See remote procedure call (RPC)

RPC Ping

A client/server utility included with Microsoft Exchange Server for testing for remote procedure call (RPC) connectivity between two locations on a network. The server portion of RPC Ping runs on an Exchange server and responds to requests from the RPC Ping client. RPC connectivity is essential between all Exchange servers in the same site.

TIP

If an RPC-based mail client such as Microsoft Outlook cannot connect to an Exchange server in its site, perform the following tests:

  1. Check network connectivity between the client and the server to try to map a network drive to a shared folder on the server by typing the Net Use command at the command prompt on the client. If this fails, you might have a hardware failure such as a failed network interface card (NIC), a loose cable, or a configuration problem with your networking protocol (such as an erroneous IP address).

  2. If network connectivity is successful, you might have a problem with the RPC binding order on the client. Try modifying this binding order in the registry.

  3. If the client still cannot connect to the server, run the server-side component of RPC Ping on the server to test which protocols RPC can bind with and which protocols can be accepted by the client. This server-side component of RPC Ping is called Rpings. Run the client-side component of RPC Ping (Rpingc32 on computers running Windows 2000, Windows NT, Windows 98, and Windows 95) to test RPC connectivity with the Exchange server. If Rpingc32 works for a specific protocol, rearrange the RPC binding order on the client so that this protocol is first.

RRAS

See Routing and Remote Access Service (RRAS)

RS-232

More properly known as RS-232C, a widely implemented serial transmission interface developed by the Electronic Industries Alliance (EIA) that is used for connecting data terminal equipment (DTE) such as computers or terminals to data communications equipment (DCE) such as modems, packet assembler/disassemblers (PADs), or serial printers. The RS-232 specification uses unbalanced lines to provide full-duplex serial communication using baseband transmission. RS-232 provides a typical data rate of 19.2 Kbps over a maximum distance of 15 meters, but the maximum data transfer rate is 115.2 Kbps. Up to two devices can be connected using RS-232. Devices cannot be daisy-chained together using RS-232. (Use RS-422/423 instead.)

RS-232 specifies the types of wires and connectors, the pinning of the connectors and the function of each wire, the voltage levels and their meanings, and control procedures such as handshaking. RS-232 cables (cables designed to use the RS-232 serial interface specification) are typically 25-wire unshielded twisted-pair (UTP) cables with DB25 type connectors or 9-wire cables with DB9 connectors. The pin assignments are shown in the following table. Note that only pins 1 through 8 and pin 20 are required for most basic RS-232 functions, which means that 9-pin DB9 connectors can be used on RS-232 serial cables for most applications.

Pin Assignments of RS-232

Pin Number Function

1

Equipment ground (for protection)

2

DTE transmit data

3

DTE receive data

4

Request-to-send (RTS), controlled by the DTE

5

Clear-to-send (CTS), controlled by the DCE

6

Data-set-ready (DSR), controlled by the DTE

7

Signal ground (common return path)

8

Carrier-detect (CD)

9

+ Voltage

10

- Voltage

11

Not used

12

Secondary received line signal indicator

13

Secondary CTS

14

Secondary DTE transmit data

15

DCE transmitter signal timing

16

Secondary DTE receive data

17

Receiver signal timing

18

Local loopback

19

Secondary RTS

20

Data-terminal-ready (DTR), controlled by the DTE

21

Signal quality detector

22

Ring indicator

23

Data signal rate selector

24

DTE transmitter signal timing

25

Test mode

NOTE

In a PC, RS-232 is typically implemented in a universal asynchronous receiver-transmitter (UART) chip, which converts the internal parallel bus signal to a serial bit stream and vice versa, enabling communication between your system bus and serial devices.

RS-232 is compatible with the V.24 and V.28 standards from the International Telecommunication Union (ITU).

TIP

You can use RS-232 with a null modem cable to connect two pieces of DTE (for example, to transfer files). If you are having trouble with an RS-232 connection, be sure that you’re using a regular cable for DTE–DCE communication or a null modem cable for DTE–DTE communication—they look the same but are incompatible.

Although the maximum speed of RS-232 is 115.2 Kbps, older PCs support rates of up to only 56 or 64 Kbps. Newer PCs have a 16550 UART chip that supports serial throughput rates of up to 460.8 Kbps.

See also FireWire

RS-422

A high-speed full-duplex serial interface that uses balanced lines and has more immunity from noise than the RS-232 interface. (An unbalanced version called RS-423 is less frequently implemented.) RS-422 is used in industrial environments with a lot of electromagnetic interference (EMI) or where more than two serial devices need to be chained together. It is typically used for high-speed synchronous communication between data terminal equipment (DTE) and multiple daisy-chained data communications equipment (DCE).

RS-422 was originally designed to supersede RS-232, but they now coexist. RS-422 typically transmits data at rates of 230 Kbps, but the speed can be increased to around 1 Mbps. The maximum distance for an RS-422 connection is typically 300 meters. RS-422 cables typically have 25 wires and use DB37 or DB9 connectors.

NOTE

Related Electronic Industries Alliance (EIA) standards include the following:

RS-422 and RS-423 are compatible with the International Telecommunication Union (ITU) V.11 and V.10 standards, respectively.

RSAC

See Recreational Software Advisory Council (RSAC)

rsh

A TCP/IP utility that enables clients to run commands directly on remote hosts without having to log on to the remote host. The remote host must be running the rsh service or daemon for this to work. Rexec, another TCP/IP utility that enables clients to run commands directly on remote hosts, does not prompt the client to enter a password upon connecting. Note, however, that rsh users must have their computer name and username configured in the remote host’s .rhosts file in order to use this command. Rsh is one of the UNIX r-commands that are available on all UNIX systems.

NOTE

Microsoft’s implementation of TCP/IP on Windows NT and Windows 2000 contains rsh client software but no rsh service. Rsh provides functionality similar to that of rexec, except rexec uses clear-text password authentication.

TIP

If a user on a computer running Windows NT or Windows 2000 is logged on to a Windows NT or Windows 2000 domain and tries to use rsh to run a command on a remote UNIX server that is running the rsh daemon, the domain controller must be available in order to resolve the username of the user, which is required by the rsh client.

run command box

A command box in Microsoft Windows 2000, Windows NT, Windows 95, and Windows 98, in which you can


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Microsoft Encyclopedia of Networking
Microsoft Encyclopedia of Networking
ISBN: 0735613788
EAN: 2147483647
Year: 2000
Pages: 37
Authors: Mitch Tulloch, Ingrid Tulloch
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