[c-nsp] LACP suspended / stand-alone states

Gilles Fabre fabre.gilles at voila.fr
Fri Apr 26 04:31:05 EDT 2013

 Hi all

However this sounds like a basic question, I can't find a correctly documented answer on that one so I decided to ask the mailing list.

I have a port-channel configured between 2 switches (SW_1/SW_2, 2 ports G0/3 & G0/4 each)
One of the ports on the port-channel goes into Suspended state (SW_1 G0/4), causing the remote one to go into Individual state (SW_1 G0/4)
(here I just did it configuring a mismatch on the interface, but this is a behaviour we have with Nexus vPC after reload)

On outputs, 1st switch interface is suspended :

SW_1(config-if)#do sh ether su
Group Port-channel Protocol Ports
1 Po1(SU) LACP Gi0/3(P) Gi0/4(s)

On 2nd switch, interface goes into Stand-alone since it doesn't receive any LACP BPDU:

SW_2#sh ether su
Group Port-channel Protocol Ports
1 Po1(SU) LACP Gi0/3(P) Gi0/4(I)

What confuses me now is that the port G0/4 on SW_1 (suspended) doesn't forward traffic (not on STP) while on SW_2 (Stand-alone) it seems to forward 
(FWD as an individual port on STP)
So does the port in Suspended state (SW_1 G0/4) still process input traffic which cames from SW_2 G0/4? or is there something I miss ?

SW_1(config)#do sh spann vlan 1
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Po1 Desg FWD 4 128.56 P2p

SW_2#sh spann vl 1
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/4 Desg FWD 4 128.4 P2p
Po1 Root FWD 4 128.56 P2p

This seems not to have any impact, but I would like to understand how it works exactly.
I thought that LACP would suspend G0/4 port on SW_2 as well as it is member of LACP channel but not forming.
I found the "port-channel standalone disable" does this on Cat65k (& an equivalent on Nexus) but nothing on 2960 or 3750; moreover, it seems it is designed for 
different designs.

Would anybody have any clue or know any good resource or link for this (rfc-like) ?

Many thanks in advance.


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