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New Member

Spanning Tree on 2950 (High CPU)

Just swapped out a 2924 with a 2950 (Copying config as closely as the 2950 would allow), and now icmp to Management IP is extremely latent (200m/sec+ from server connected directly to it)....icmp through the 2950 is unaffected.

Spanning tree appears to be the culprit:

36 12275368 3206214 3828 4.99% 4.07% 4.05% 0 Spanning Tree

2950 connects to Cat4k on multiple ports (Both trunks/Non Trunks)

spanning-tree mode is pvst on 2950.

Hoping someone has come across this before :)

Regards,

MB

2 REPLIES
Cisco Employee

Re: Spanning Tree on 2950 (High CPU)

I would not be too worried about ICMP response to the switch itself. Most switches have low priority for ICMP destined for itself. Also 4% CPU in STP doesnt seem a lot to me. To be sure, check for any excessive STP TCNs, clear off not needed VLANs off the trunks.

New Member

Re: Spanning Tree on 2950 (High CPU)

Further investigation revealed that all the cat4k's vlans where in the 2950's dynamic table (show mac-address-table dynamic) - These vlans where definitely not supposed to be there, so I checked out the interconnecting ports(On Cat4k) to discover that about 5 had turned into trunk ports!(Does CatOS automagically enable trunking on ports in certain circumstances?)

Systematically disabling trunking on these ports stopped all the cat4k's vlans being advertised to the 2950, and also reduced the cpu of spanning tree:

36 15213172 3875075 3925 1.14% 1.37% 1.61% 0 Spanning Tree

icmp had now also dramatically reduced.

Regards,

MB

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