From: NSN - CO/Santa Fe de Bogota ("Gutierrez,)
Date: Thu Nov 20 2008 - 19:49:01 ARST
Just use broadcast storm control to diminish the loop impact processor
wise and to define the broadcast threshold allowed as per interface, in
that way it will give you more time to track down the source of the
problem or at least time enough to disconnect all secondary layer 2
redundancy, loops are lethal and can bring down your network in a matter
of seconds,
Rodrigo
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
>Behalf Of ext Antonio Soares
>Sent: Thursday, November 20, 2008 4:43 PM
>To: 'Kim teu'; 'Cisco certification'
>Subject: RE: Layer 2 loop breaks OSPF adjacency over Layer 3 links
>
>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_n
>ote09186a0080136673.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
>
>
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