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

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Jan 7th, 2010
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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.

Correct Answer by Giuseppe Larosa about 7 years 3 months ago

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

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Correct Answer
Giuseppe Larosa Thu, 01/07/2010 - 11:05
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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

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