TCPIPConcepts


TCP/IPConcepts

TCP/IP is a protocol that was originally implemented on Unix platforms but has now become the default network protocol on Microsoft Windows , Novell NetWare, and Apple Macintosh computing platforms. TCP/IP is routable and can be used for both local area networks and wide area networks. You should use TCP/IP if:

  • Your network is heterogeneous in character, consisting of different computing platforms and operating systems that all need to work together.

  • You need connectivity with the Internet or want to deploy Internet technologies within a corporate intranet environment.

  • You want to use the Active Directory component of WS2003. (Active Directory requires TCP/IP.)

A full treatment of TCP/IP is beyond the scope of this book. What follows here is a brief summary of its important features. For more information, see TCP/IP Network Administration by Craig Hunt (O'Reilly).

Some of the advanced features of TCP/IP in WS2003 include:

  • Support for APIPA, which allows client computers to be assigned IP addresses automatically without the need of a DHCP server. See Automatic Private IP Addressing (APIPA) later in this section for more information.

  • Support for dynamic recalculation of TCP window size and the ability to use large TCP windows to improve performance when large amounts of data are transmitted during a session. See Request For Comment (RFC) 1323 at www.ietf.org/rfc/ for more information.

  • Support for selective TCP acknowledgments to reduce the time retransmitting lost packets. See RFC 2018 for more information.

  • Support for the TCP Round Trip Time Measurement option of RFC 1323 to improve performance over slow WAN links.

  • Support for caching of resolved DNS name queries on client resolvers .

  • Support for ICMP Router Discovery for discovering router interfaces that aren't assigned manually or through DHCP. This feature is enabled using the Routing and Remote Access console, and a description of the feature can be found in RFC 1256.

  • The ability to disable NetBIOS over TCP/IP (NetBT) for specific network connections. This feature improves performance when DNS is the only name-resolution method in use on the network. This is really an all-or-nothing decision, as a WS2003 computer with NetBT disabled can use Client for Microsoft Networks to connect to other WS2003 computers running File and Print Sharing for Microsoft Networks only if those computers also have NetBT disabled. Disabling NetBT means the computer can no longer use NetBIOS name-resolution methods such as WINS servers or lmhosts files. In most cases, you will not use this feature as most networks will consist of a mix of WS2003 and legacy Windows clients and servers. For information on how to disable NetBT, see WINS later in this chapter.

IP Addressing

Each host (computer, network printer, router interface, and so on) on a TCP/IP network is generally characterized by three pieces of information:

IP address

A logical 32 bit address that uniquely identifies the host on the network. IP addresses are expressed in dotted decimal form and consist of four octets separated by decimals with each octet ranging from 0 through 255 (with some restrictions). An example of an IP address might be 172.16.11.245.

Subnet mask

A 32 bit number that divides the IP address into two parts a network ID, which uniquely identifies the network that the host resides on, and a host ID, which uniquely identifies the host on that particular network. For example, the subnet mask 255.255.0.0, when applied to the IP address 172.16.11.245, indicates that the network ID of the host is 172.16, while the host ID of the host is 11.245.

Default gateway

A 32-bit address that identifies the default router interface to which to send packets that are directed to another network (or, more accurately, that are directed to a different subnet on a TCP/IP internetwork) if no other route is specified. The default gateway is optional and is necessary only on networks consisting of more than one subnet or when packets are being sent between different networks.

Managing TCP/IP

One aspect of managing TCP/IP is managing IP addresses on your network. WS2003 lets you assign IP addresses and other TCP/IP settings in three different ways:

Manually by using static IP addresses

This method is suitable only for small deployments of fewer than a hundred machines or so. TCP/IP settings must be configured at the local console of each machine, so this method is unsuitable if the hosts are geographically separated. Since errors in assigning IP addresses can cause general problems with network communications, this method can be a lot of work to troubleshoot.

Automatically by using DHCP

This is the default method for assigning TCP/IP settings on WS2003 machines. It uses one or more Dynamic Host Configuration Protocol (DHCP) servers, which maintain pools of available IP addresses, which lease these addresses to client computers that request them. DHCP should always be used on medium- to large-scale networks that run TCP/IP. DHCP can also be used by legacy Microsoft Windows platforms to configure TCP/IP on machines.

Automatic Private IP Addressing (APIPA)

If your WS2003 machine is configured to obtain an IP address by DHCP but no DHCP server is available on the network, the machine opts for assigning itself an address using APIPA. This method is an alternative to using DHCP on small- to medium-scale networks that use WS2003 and run DHCP. For more information, see the next section.

Automatic Private IP Addressing (APIPA)

APIPA is an extension of DHCP that allows computers to self-configure their IP address and subnet mask without a DHCP server. The way it works is that a computer uses APIPA to randomly select a unique IP address from a block of IP addresses reserved by Microsoft for this purpose. This reserved IP block covers the address range 169.254.0.1 through 169.254.255.254 and, together with the subnet mask 255.255.0.0, provides enough addresses for 64,024 hosts running on a single subnet. In real life, however, APIPA is intended for use on home or small business networks containing at most a few dozen machines, because:

  • Only the IP address and subnet mask can be assigned using APIPA, and not default gateways or other TCP/IP settings that can be provided by DHCP servers and that are needed by TCP/IP networks connected to other networks or to the Internet.

  • Only a single subnet can be created using APIPA, which is not of much use in an enterprise-level network.

To configure a computer to use APIPA, simply configure it to obtain an IP address automatically. Then, when the machine restarts, it first tries to contact a DHCP server, and if this fails, APIPA then kicks in and the machine selects an IP address for itself of the form 169.254. x.y . It then tests the uniqueness of the address on the network by broadcasting a DHCP-type message to the rest of the machines on the network to find out if any other machine is using this address. If no other machine responds saying that it has taken that address, it assigns the address to itself along with the subnet mask 255.255.0.0. If, however, another computer claims to already be using the address, APIPA generates another address at random until a usable one is found. Then, should a DHCP server later be installed on the network, computers that used APIPA to select an address will soon detect the DHCP server and request a new IP address and other TCP/IP settings from the server.

APIPA can cause problems on large networks, however. For example, if a DHCP server goes down and client computers can't renew their leases, they would start using APIPA to assign themselves addresses. This would result in communications on the network breaking down because the machines that acquired new addresses using APIPA would be on a different subnet from those still holding their leased DHCP addresses. The solution is to disable APIPA entirely, but, unfortunately , the only way to do this is to use the registry. You disable APIPA on a specific network adapter by creating a new key called IPAutoconfigurationEnabled of type REG_DWORD within the subkey :

 HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\GUID_of_ network_adapter\ 

and assigning this new key the value 0. Change the value to 1 to reenable APIPA on the adapter. On a multihomed machine with multiple network adapters, you can disable APIPA on all adapters by placing the IPAutoconfigurationEnabled key within the subkey:

 HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ 

If there are network connections that aren't being used on servers (most importantly, domain controllers), they should either be disabled or have APIPA disabled. Otherwise, clients may get incorrect IP addresses when querying DNS.

Troubleshooting TCP/IP

WS2003 includes a comprehensive set of command-line utilities for testing and troubleshooting TCP/IP configurations and networks, including arp , ipconfig , nbtstat , netstat , pathping , ping , route , and tracert . For more information on these utilities, see Chapter 5.



Windows Server 2003 in a Nutshell
Windows Server 2003 in a Nutshell
ISBN: 0596004044
EAN: 2147483647
Year: 2003
Pages: 415
Authors: Mitch Tulloch

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