Cisco 6500's in VSS Configuration. Port channel ID's

[NetSockets]

Hello,

I have a pair of 6500's setup with VSS and there is currently only one link between then. However one end of the link is on Po10 and the other end is on Po25.  If I move the Po25 over to Po10, will things break? It seems to be working fine now. I'm about to add a second link and I'm concerned about the current configuration.  It makes more sense to me to have both ends of the same link on the same port-channel ID.  I've seen documentation which states otherwise however.

interface Port-channel10

no switchport

no ip address

switch virtual link 1

mls qos trust cos

no mls qos channel-consistency

!        

interface Port-channel25

no switchport

no ip address

switch virtual link 2

mls qos trust cos

no mls qos channel-consistency

DTC_6509s_VSS#sh run int Te1/5/4

Building configuration...

Current configuration : 116 bytes

!

interface TenGigabitEthernet1/5/4

no switchport

no ip address

mls qos trust cos

channel-group 10 mode on

end

DTC_6509s_VSS#sh run int Te2/5/4

Building configuration...

Current configuration : 116 bytes

!

interface TenGigabitEthernet2/5/4

no switchport

no ip address

mls qos trust cos

channel-group 25 mode on

end

DTC_6509s_VSS#

DTC_6509s_VSS#sh vslp lmp sum

Instance #1:

  LMP summary

    Link info:        Configured: 1        Operational: 1

                            Peer Peer          Peer   Peer      Timer(s)running

Interface Flag State        Flag MAC           Switch Interface (Time remaining)

--------------------------------------------------------------------------------

Te1/5/4   vfsp operational  vfsp 0026.0a26.84c0 2      Te2/5/4   T4(24ms)

                                                                 T5(59.95s)

DTC_6509s_VSS#sh switch virtual link port-channel

Flags:  D - down        P - bundled in port-channel

        I - stand-alone s - suspended

        H - Hot-standby (LACP only)

        R - Layer3      S - Layer2

        U - in use      N - not in use, no aggregation

        f - failed to allocate aggregator

        M - not in use, no aggregation due to minimum links not met

        m - not in use, port not aggregated due to minimum links not met

        u - unsuitable for bundling

        d - default port

        w - waiting to be aggregated

Group  Port-channel  Protocol    Ports

------+-------------+-----------+-------------------

10     Po10(RU)         -        Te1/5/4(P)    

25     Po25(RU)         -        Te2/5/4(P)    

[Mohamed Sobair · Accepted solution]

Hello,

It doesnt make a difference if you make both sides with the same channel id or not. The port channel ID  is a logical interface that doesnt have impact on the etherchannel between both sides at all. So you can leave one side as Po10 and the other as Po25 without a problem. Just make sure you have at least one member of the Portchannel physical interfaces Active in order not to loose your VSS connection.

Regards,

Mohamed

[krahmani323]

Hello NetSockets,

Here the important fact is the two port-channel Po10 and Po25 are the two special port-channels used to build the VSL link between both chassis (switch virtual link under the Po configuration) .

The two VSL port-channel IDs are parameters that need to be unique in order for the the two chassis to constitute the VSS.

http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/VSS30dg/VSS-dg_ch2.html#wp1056015

Configuring VSL Bundle

The VSL bundle is a special-purpose port channel. Each standalone switch is required to be configured with unique port-channel interface numbers; before assigning a port-channel number, you must make sure that the port-channel interface number is not used by an existing standalone configuration on either switch;

Moreover even if you try to change the VSL Po ID of Te2/5/4 from 25 to 10 it will not be allowed as « … a neighbor switch port cannot be bundled into the local switch's VSL EtherChannel. ….., the Switch 1 VSL EtherChannel cannot bundle a physical port from Switch 2 »

You would have something like =>

DTC_6509s_VSS(config-if)# int te2/5/4

DTC_6509s_VSS (config-if)# channel-group 10 mode on

VSL bundle across chassis not allowed TenGigabitEthernet2/5/4 is not added to port channel 10

(In general, before migrating to VSS I like to define Po1 and Po2 for the VSL port-channel for easy identification, but you can perfectly continue with those Po numbers. Indeed as you VSS is in production it would be very heavy to change the VSL Portchannel n°)

If you want too add another link to the VSL just make sure to use the same configuration on the new links (here msl qoS config line)..

Hope that helps.

Karim