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New Member

Device not using configured loopback

Hi guys,

I have a 1712 running 12.2(15)ZL1 which is not using the configured loopback0 for SNMP returns.

Connectivity works fine using loopback, but just no joy when snmpwalking :(

I have enabled detailed debugging and can see it is using the serial IP address of the exit interface nearest to my managememt station.

So, anybody seen this supposed bug before?

Hall of Fame Super Silver

Re: Device not using configured loopback


I suspect that the router is obeying the configured snmp-server trap-source command. But it is not intended to do what you expect it to do. This command specifies which interface to use as source when the router generates a trap. But snmpwalk is not based on traps, it is based on snmp query (get, getnext, etc) and response which is quite different from traps.

My suggestion is to do something on the router that will generate a trap and see what is the source address. (I suspect that it will be the loopback)



New Member

Re: Device not using configured loopback

Cheers Rick,

I thought that may be the case, so many thanks for the clarification. I must admit the command name "snmp-server trap-source Loopback0" does kind of spell out what it does.

My working devices are successfully using their loopback0 address as the source of an SNMP reply to my management system ..... but the devices that are not working are using the IP of the exit interface closest to my management system. For comparison testing I removed the command from the working units and it made no difference. I should have done that before I posted this thread!

I suspect the best thing is to upgrade to a later version and test then. This box is running an ED so is probably full of bugs (Version 12.2(15)ZL1, EARLY DEPLOYMENT RELEASE SOFTWARE (fc1))