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Core 6509 issue with STP

mohammad saeed
Level 5
Level 5

Hi guys,

I have one strange issue about 6509, the case is when i disconnected the VSS link physically in SW standby and both switches were run (SW1 Active and SW2 Standby) then suddenly I lost the connection all of my edge switches connected with two 10 Gig links and every link port-channels went down! why that happened?

I checked edge switches 2960s all ports connected with core is in error disable state I tried to turn it on again but no hope and i checked the spanning tree I found it is the root and my core sw is the root as well!

I restarted my both core switches and edge switches the every thing goes fine!

But my question hy did that happens when I removed the VSS cables? but when I shutdown one core every things fine!

Thanks

Mohammad

3 Replies 3

Mark Malone
VIP Alumni
VIP Alumni

Did you collect console logs from the switches when you were pulling the link , it will help identify what exactly happened ?

what way is you VSS setup configured ?

Hi All,

Actually I didn't have enough time to collect data because it's big project and is working so I solved quickly through restarting two cores and edge sw!

What happened is all my edge switches became as a Root in STP status and blocked their interfaces by error disable. I think it's STP issues. before the Core sw STP proirity was 24576 could be that problem?

Michael Eaves
Cisco Employee
Cisco Employee

Not a strange issue, actually is expected.  If you disconnected the ISL link between the VSS pair (active/standby), they don't think they are in a pair anymore or they think the other switch is down so both go active/active.  Because you cannot have an edge switch connected to two separate upstream switches, the edge switches error.

A VSS pair is a single logical switch and two physical switches.  When the ISL is broken (keep alives fail) so they are then two physical switch and two logical switches.  You can get around the active/active scenario by shutting one down or replacing the ISL cables. 

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-virtual-switching-system-1440/109547-vss-best-practices.html?referring_site=bodynav#vsl_llr

VSL Link Loss and Recovery

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