I need help to understand the error message: %CLNS-3-BADPACKET: ISIS:

[Erick Vaiano de Freitas]

During some tests (7206VXR NPE-G2), placing an interface GigabitEthernet in loop, the router was unstable and showed these error messages:

Dec 23 15:41:10: %CLNS-3-BADPACKET: ISIS: LAN L2 hello, Duplicate system ID detected from 001d.a19a.ac19 (GigabitEthernet0/3)

Dec 23 15:42:10: %CLNS-3-BADPACKET: ISIS: LAN L2 hello, Duplicate system ID detected from 001d.a19a.ac19 (GigabitEthernet0/3)

I’m looking for a BUG.

Somebody knows why this is happening? Is not recommended close loop in Ethernet interfaces with IS-IS?

Thanks.

[Giuseppe Larosa · Accepted solution]

Hello Erik,

>> During some tests, placing an interface GigabitEthernet in loop,

the message is originated from the fact that the router receives its own Hellos back.

We use ISIS and this is a sign of a bridging loop when it happens in a campus network.

Nothing to worry about you have made a loop and ISIS detected it.

I would say it is good news

if it happens in production it is bad news sign of a bridging loop as I've written before

Hope to help

Giuseppe