Cisco 2524 Serial Interface OIDs

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Jun 18th, 2008

Hello All. We are using a Cisco 2524 router. We would like to be able to monitor the serial port utilization on this router using snmp. What is the correct OID to use for this? Thanks for your help in advance.

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hennigan Wed, 06/18/2008 - 15:23

It varies as the interface ID is a number and not specific to an interface type. In other words, there isn't an OID specific to "ethernet 0", only "the first interface on this platform".

You need to do two things.

1. configure "snmp-server ifindex persist" in global config mode so that the indexes don't change on a reload.

2. snmpwalk the interfaces and correlate the index number with the ifDescr to determine which to poll.

For example:

$ snmpwalk -c public r1.foo.com interfaces

IF-MIB::ifIndex.1 = INTEGER: 1

IF-MIB::ifIndex.2 = INTEGER: 2

IF-MIB::ifIndex.6 = INTEGER: 6

IF-MIB::ifIndex.7 = INTEGER: 7

IF-MIB::ifIndex.8 = INTEGER: 8

IF-MIB::ifIndex.9 = INTEGER: 9

[snip]

IF-MIB::ifDescr.1 = STRING: FastEthernet0/0

IF-MIB::ifDescr.2 = STRING: FastEthernet0/1

IF-MIB::ifDescr.6 = STRING: Null0

IF-MIB::ifDescr.7 = STRING: Loopback0

IF-MIB::ifDescr.8 = STRING: Serial1/0

IF-MIB::ifDescr.9 = STRING: Serial1/1

[snip]

The configuration maker in MRTG and most similar packages is pretty good at sorting it out automagically, doing the walk and generating the configuration.

Just be sure to set the "snmp-server ifindex persist" command before you walk it the first time. This is more critical on modular routers where WICs, NMs, PAs, etc. can be added or removed, but can also bite you if subinterfaces, loopbacks, tunnels and the like are added or deleted. Without it the OID of a particular interface can change on reboot.

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