From: Antonio Soares (amsoares@netcabo.pt)
Date: Thu Nov 20 2008 - 19:42:37 ARST
A STP Loop can stop everything in your network. I saw an entire data center going down in less than 1 second! When this is
happening, the best to do is to break every existent L2 redundant link quickly. In some situations, if you don't have physical
access to the equipments, this is just not possible!
Then when the storm is over, you can try to trace the source of the problem. But i can tell you it's very difficult or even not
possible to find out what failed.
Cisco has a good document about this:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080136673.shtml
Regards,
Antonio Soares, CCIE #18473 (R&S)
amsoares@netcabo.pt
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Kim teu
Sent: quinta-feira, 20 de Novembro de 2008 14:55
To: Cisco certification
Subject: Layer 2 loop breaks OSPF adjacency over Layer 3 links
Hello all,
*Has anyone experienced a layer 2 loop event that caused OSPF adjacency to be dropped for layer 3 links? Any idea why?*
**
*What's the best way to diagnose the cause of the layer 2 after the outage?
The following is what I see in the log.** VLAN 56 is looping...*
*The switch is seeing packet sourced from itself::*
>>>472825: .Nov 19 15:38:56 CST: %STANDBY-3-DUPADDR: Duplicate address
192.168.97.1 on Vlan56, sourced by 0017.df1c.6800
*The standby state change to active because the switch lost it connection to the active switch because of SPT loop prevention::*
>>>472826: .Nov 19 15:39:00 CST: %STANDBY-6-STATECHANGE: Vlan72 Group 72
state Standby -> Active
>>>472827: .Nov 19 15:39:03 CST: %STANDBY-6-STATECHANGE: Vlan116 Group
>>>116
state Standby -> Active
>>>472828: .Nov 19 15:39:26 CST: %STANDBY-3-DUPADDR: Duplicate address
192.168.97.1 on Vlan56, sourced by 0017.df1c.6800
>>>472829: .Nov 19 15:39:38 CST: %STANDBY-6-STATECHANGE: Vlan152 Group
>>>152
state Active -> Speak
>>>472830: .Nov 19 15:39:47 CST: %OSPF-5-ADJCHG: Process 10, Nbr
192.168.200.5 on Vlan704 from EXSTART to DOWN, Neighbor Down: Dead timer expired
>>>472831: .Nov 19 15:39:54 CST: %STANDBY-6-STATECHANGE: Vlan134 Group
>>>134
state Active -> Speak
>>>472832: .Nov 19 15:39:56 CST: %STANDBY-3-DUPADDR: Duplicate address
192.168.97.1 on Vlan56, sourced by 0017.df1c.6800
>>>472833: .Nov 19 15:39:59 CST: %STANDBY-6-STATECHANGE: Vlan152 Group
>>>152
state Standby -> Active
>>>472834: .Nov 19 15:40:14 CST: %STANDBY-6-STATECHANGE: Vlan134 Group
>>>134
state Standby -> Active
Kim
Blogs and organic groups at http://www.ccie.net
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