VSS - failure

Unanswered Question
Feb 27th, 2009


I have one question about VSS.

I'm configuring VSS with two 6500 chassis, both have one sup. I don't have 10G module, so there is only one connection (two cables in etherchannel).

So, I'm testing VSS redundancy, and I pull out these cables. There is some possibility that someone can do something like that in real world :). After that I have two ACTIVE supervisors, and uplink ports (configured for ether-channel) on access switches goes to errdisable state!!

So, my whole network depends on these two cables!!

So, I need to configure errdisable recovery on all access switches or you have some better idea?

I would like to hear your opinion.



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
vjemin Mon, 03/02/2009 - 03:24


well now I configured PAGP and fast-hello detection.

Fast-hello works fine, but with PAGP I have some problems.

I got that the other switch is not dual-active detect capable.

Other switches are 3560 and 2960 and etherchannel is mode desirable. Versions are c3560-ipbase-mz.122-35.SE5.bin and c2960-lanbase-mz.122-44.SE3.bin.

What else do I need to configure or upgrade software or something else?



Giuseppe Larosa Mon, 03/02/2009 - 05:09

Hello Vlaho,

here you can find a list of devices that support Enhanced PAGP needed for dual active detection


I think you should switch to BFD over a dedicated etherchannel because the original config guide document speaks of C6500 with Sup32 or Sup720 as capable to process the new TLV for VSS.

In fact, also the product overview for C3750 12.2(46)SE doesn't list enhanced PAGP.


You can use concurrently BFD and fast-hello detection, that is better then relying on a third device (according to me)

Hope to help


vjemin Tue, 03/03/2009 - 07:24

Hi Giuseppe,

well, I have upgraded all my switches and now it works fine.

Enhanced PaGP and fast-hello work fine, and I will use both metods for dual-detection.

Thanks a lot for quick answers



Giuseppe Larosa Tue, 03/03/2009 - 08:39

Hello Vlaho,

good news to know that you solved your issue.

if I've correctly understood with the correct IOS image the C3750 and C2960 can pass the new TLV of enhanced PAGP ?

Best Regards


vjemin Tue, 03/03/2009 - 23:59

Hello Giuseppe,

it's right. With new IOS images everything works fine.




This Discussion