Appendix C. SNMP MIB Structure


  • SNMP information in a router is organized as a Management Information Base (MIB).

  • A network management system can use SNMP to access data stored in the MIB.

  • MIBs represent data as a hierarchical tree structure; each MIB variable is referenced by its object identifier (OID).

  • OIDs are formed by concatenating the name or number of a tree branch as the tree is followed from the root to the object's location, in dotted notation.

Figure C-1 shows the top layers of the standard MIB tree. The root layer is unnamed. All MIB variables that are useful for network management are located under the internet subtree . Following the tree structure downward, internet is referenced as OID iso. org. dod. internet, or 1.3.6.1.

Figure C-1. Top-Level MIB Structure

graphics/apcfig01.gif

The iso. org. dod. internet. mgmt subtree (1.3.6.1.2) contains many useful objects, all organized under the mib subtree (1.3.6.1.2.1). These objects fall into the following categories:

  • system ” Descriptions of the system or router, uptime, and network services

  • interfaces ” Parameters and counters for each interface

  • at ” Address translation mappings for media- (MAC) to-IP addresses

  • ip ” IP packet counters, IP routing tables, and IP-to-MAC address mappings

  • icmp ” Counters of ICMP message types seen

  • tcp ” TCP segment counters and connection tables

  • udp ” UDP datagram counters and port tables

  • egp ” Exterior Gateway Protocol (EGP) counters

  • transmission ” Media-specific MIBs

  • snmp ” SNMP counters

The experimental (1.3.6.1.3) subtree can contain MIBs that are new and experimental in nature. However, experimental MIBs can also be introduced into the standard mib subtree (1.3.6.1.2).

The private (1.3.6.1.4) subtree contains one subtree, enterprise (1.3.6.1.4.1), where all network vendor-specific objects are located. The Cisco private MIB structure is contained in the cisco subtree (1.3.6.1.4.1.9). The set of specific MIBs that are included under the cisco MIB tree varies according to the hardware platform and the IOS software release level.

A good resource for referencing and downloading MIBs is the Cisco MIBs page on CCO:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

Through the tools offered , you can do the following:

  • MIBs supported by product ” Browse through listings of available MIBs, based on a choice of hardware platform. The MIB listings are then broken down by IOS release level, showing MIBs that have been added to each release.

  • OID ” Find the OID (dotted decimal notation) of specific Cisco MIBs and features.

  • SNMP v1 MIBs ” Download the actual SNMP v1 MIB files.

  • SNMP v2 MIBs ” Download the actual SNMP v2 MIB files.

TIP

You can also use the undocumented show snmp mib command to see a list of MIB objects that are available on a router. Although this command lists the objects in a short format (without OIDs), it can be useful to find the names of specific MIB variables.




Cisco Field Manual[c] Router Configuration
Cisco Field Manual[c] Router Configuration
ISBN: 1587050242
EAN: N/A
Year: 2005
Pages: 185

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