Originally, SNMPv1 specified that SNMP should operate over the User Datagram Protocol (UDP) and IP. The SNMPv2 transport mapping document (RFC 1449) defines implementations of SNMP over other transport protocols, including OSI Connectionless Network Service (CLNS), AppleTalks Datagram Delivery Protocol (DDP), and Novells Internet Packet Exchange (IPX). RFC 1449 also includes instructions on how to provide an SNMPv1 proxy and use of the BER. TCP/IP is still SNMPv2s preferred transport mapping because UDP is compatible with SNMPv1 at both the transport and network layers.
Ciscos SNMP Implementation
Cisco Systems currently includes SNMP support in every router and communications server. Cisco SNMP agents communicate successfully with all SNMP-compliant NMSs, including those of Sun Microsystems (SunNet Manager), IBM (NetView/6000), and Hewlett-Packard (OpenView). The following section discusses how Cisco has implemented SNMP within its products.
SNMP Version Co-Existence
Cisco is a member of the Internet Engineering Task Force (IETF), and is active in defining the SNMPv2 and SNMPv3 standards. When the standards are final, Cisco will support the SNMPv2 and SNMPv3 agents in its access equipment operating systems. Until SNMPv3 becomes a standard, Cisco equipment will be bilingual, supporting both SNMPv1 and SNMPv2.
Bilingual support of SNMP gives users flexibility by enabling them to migrate to SNMPv2 on their own timetables. During the period when SNMPv1 and SNMPv2 coexist, Cisco customers will not lose any management functionality. Cisco routers will be able to communicate with both SNMPv1 and SNMPv2 Network Management Systems (NMSs).
RFC 1452 defines a SNMPv1/v2 coexistence strategy. This strategy defines two basic techniques: a proxy agent and a bilingual Network Management System. The proxy agent translates information between SNMPv1 and SNMPv2 messages. The bilingual Network Management System (NMS) incorporates both SNMPv1 and SNMPv2 manager software, and, therefore, can communicate with both types of agents. When communication with an agent is required, the manager selects the appropriate protocol.
Ciscos bilingual agent support will work with both the proxy agent and the bilingual Network Management System (NMS) coexistence strategies, but neither will be a requirement. Because bilingual agents can communicate equally well with both SNMPv1 and SNMPv2 NMSs, users will not be forced to purchase additional SNMPv2 manager software or proxy agents. Depending upon the extent of changes within the forthcoming SNMPv3 standard, covered in Chapter 12, a similar strategy is anticipated that allows for the incorporation of SNMPv3 into network devices and Network Management Systems.
System Monitoring and Management Capabilities
Cisco routers provide many useful system monitoring and management capabilities to help administrators manage large Cisco router-based internetworks. System statistics can be tracked both by interface and by protocol. For example, administrators can query for, and receive, the number of cyclic redundancy check (CRC) errors on a particular interface or the number of AppleTalk packets sent to, or received from, an interface. This kind of information is an invaluable component of baselining your network performance.
Cisco routers also can report a wide variety of information about their internal configuration and status. For example, engineers and managers can determine the following:
Ciscos MIB Extensions
With over 450 objects, Ciscos private MIB provides network managers with broad, powerful monitoring and control facilities. Ciscos private MIB supports DECnet (including DECnet routing and host tables), XNS, AppleTalk, Banyan VINES, Novell NetWare, and additional system variables that highlight such information as average CPU utilization over selectable intervals. Furthermore, Cisco developers can add private extensions to the MIB as required. This capability gives managers the flexibility to mold Ciscos SNMP products to their own networks, optimizing management capabilities. Figure 9-10 illustrates Ciscos private MIB tree. This figure expands upon the lower right section of the diagram shown in Figure 9-5.
Cisco also supports other MIBs relevant to router operation. For example, support for some chassis MIB objects enables users to retrieve information about router chassis and installed cards. Card types, card serial numbers, the number of cards in a particular router, the ROM version of those cards, and many other useful variables can be retrieved. Support for the chassis MIB eases network administration. Those responsible for network maintenance can remotely query Cisco routers to quickly discover a routers hardware configuration, thereby saving time and money. This ability is provided through the use of Ciscos private MIB, as shown in Figure 9-11.