What is Best Practice for Local SPAN on Cat 6800 VSS (w/ MEC source)?

[TomBowles71813]

In order to avoid SPAN traffic from traversing the VSL, the 6500 VSS best practice guide says to use two separate monitor sessions, one for each chassis, sourcing the SPAN traffic from MEC member interfaces (not the Po int).

However, the 6800 config guide states:

"A port-channel interface (an EtherChannel) can be a SPAN source, but you cannot configure active member ports of an EtherChannel as SPAN source ports.”

What is the best practice for Local SPAN on the Cat 6800 VSS (all links are MECs)?

Thanks,

Tom

[balaji.bandi]

Follow below thread already addressed :

https://community.cisco.com/t5/switching/vlan-span-on-catalyst-vss/td-p/4080659

[TomBowles71813]

That thread refers to something different: restrictions when using VSL as SPAN ingress.

To clarify, I need to know how to configure Multichassis EtherChannel as SPAN ingress without pulling massive amounts of SPAN traffic across the VSL.

[balaji.bandi]

The post is still valid. since we need to consider design consideration as part of the product design deployment and understand the limitation before we expect the outcome.

VSS Means a single Logical switch, it depends on how you configured your MEC.

Technically MEC will be done due to redundancy, so each port belongs to the individual they are part of VSS.

So if your MEC only comes from one device you do not see any issue, but again your requirement can be addressed in a different way, where you can use the exit point to configure or span the traffic depends on the design.

[Reza Sharifi]

Hi,

I would make the Pochannel the source. The other option may be the vlan interface if the SVI is located on 6800.

monitor session xx source interface port-channel xx

HTH

[TomBowles71813]

Hi Reza,

How do I configure the egress interface to prevent SPAN from traversing the VSL?

Do I use one physical interface on each switch?

[Reza Sharifi]

Hi Tom,

That is what we have configured on the 6800 in the past. One port per switch e.g gi1/1/1 and 2/1/1.

Have never tested it with one switch port and see the effect on the VSL. Overall, the VSL links should not have much traffic traversing them if all access switches are connected to both 6800.

HTH

[TomBowles71813]

Hi Reza,

Thanks for your help on this. Unfortunately the 6800 doesn’t accept this config, and the 6800 documentation states “...you cannot configure active member ports of an EtherChannel as SPAN source ports.”

This CiscoLive slide deck (pg 49) says to use MEC for destination and then ‘port-channel min-links’ to prevent one leg of the MEC from being active and causing VSL oversubscription. However, ‘port-channel min-links’ on the 6800 is only supported on LACP MECs, but SPAN destination MECs must be “channel-group mode on”…. Lot’s of dead ends.


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