VSS using Pagp+ Dual Active Detection

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Oct 31st, 2008
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I am going to use VSS with a C3750 'Access' switch running 12.2(46)SE that supports Pagp+ for dual active detection. Regarding this topology, i have some questions:

1) Does my Etherchannel towards the C3750 stack need to be a Pagp Etherchannel ? Or can it be a fixed Etherchannel (mode on) ?

2) If the Etherchannel needs to be a Pagp Etherchannel before VSS can use the Pagp+ packets, does this imply that i can't use a cross-stack Etherchannel on the C3750, because cross-stack etherchannel did not support Pagp before ? Is it supported on 12.2(46)SE ?

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jevogler Sat, 11/01/2008 - 22:30
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If you intend to use stackwise, you will need to use LACP.

I would leave one 3750 "unstacked" and use enhanced pagp for dual active detection. This will reduce dual active detection times dramatically at the cost of managing an extra device.

Note... An upcoming software release will introduce a new method for detection, -so this will only be a short term fix. When you migrate to the new code you can restack the enhanced pagp 3750 and add it to your lacp bundle.

gnijs Wed, 11/19/2008 - 12:31
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i checked the new SXI release with L2 fast-hello's. Work perfect and much better than BFD.

Michael Strnad Thu, 11/20/2008 - 09:02
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You mentioned L2 fast-hello's, can you provide some configuration samples?

gnijs Fri, 11/21/2008 - 03:53
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It is -very- easy to configure.

Just connect two interfaces back-to-back together, of course, following a different path as your VSL links, then:

interface GigabitEthernet2/4/14

no switchport

no ip address

dual-active fast-hello


interface GigabitEthernet1/4/14

no switchport

no ip address

dual-active fast-hello


And that's all.

VSS_SWITCH#sh switch virtual dual-active fast-hello

Fast-hello dual-active detection enabled: Yes

Fast-hello dual-active interfaces:

Port Local State Peer Port Remote State


Gi1/4/14 Link up Gi2/4/14 Link up

jerry_best Fri, 11/21/2008 - 07:20
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Hi All,

Planning to implement VSS in my network just waiting for delivery of 6509-E with VSS boxex. but i don't know anything about the vss.

can somebody give me cisco URL where i can understand concept of VSS and sample configuration.

Thanks and Regards,



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