VLAN SPAN on Catalyst VSS?

[AJ Cruz]

Hello I can't find any clear documentation on how SPAN works in a VSS environment. I see in the documentation that you cannot configure SPAN on a VSL, but my question is regarding SPAN with a VLAN source.

I assume both chassis will capture traffic from the VLAN and send the traffic over the VSL (if necessary) to the destination port.

Is that correct?

Or does it never cross a VSL (stays local) in which case I'd have to configure two SPAN sessions and two physical destinations (one on each chassis) to capture all the traffic?

Thanks.

[pkumari4]

Hello Cruz,

SPAN Support with VSS.

The VSS supports all SPAN features for non-VSL interfaces.

The VSS supports SPAN features on VSL interfaces with the following limitations:

*VSL ports cannot be a SPAN destination.

*VSL ports cannot be an RSPAN, ERSPAN, or egress-only SPAN source.

*If a VSL port is configured as a local SPAN source, the SPAN destination interface must be on the same chassis as the source interface.

*SPAN copies are always made on the chassis where the ingress port is located.

*Two VSLs cannot share the same SPAN session.

*A pair of LTL indices are used to avoid duplicate SPAN copies across VSL interfaces. The number of SPAN sessions available to a VSS is the same as for a single chassis running in standalone mode.

With a VSL port as a SPAN source, the following limitations apply:

*The SPAN destination must be on the same chassis.

*Port-channel interfaces cannot be the SPAN destination. http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/15-0SY/configuration/guide/15_0_sy_swcg/virtual_switching_systems.html#wp1241589

You can also find the best practices for VSS at the following link: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-virtual-switching-system-1440/109547-vss-best-practices.html#span

Now coming back to your original question there are no limitations for non VSL ports. So if you are taking the SPAN on non-VSL port even though those ports under that specific VLAN are not part of the same chassis still you will be able to get capture.

Please check link here:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/con figuration/guide/vss.html#wp1054844

General Guidelines & Restrictions for SPAN:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/con figuration/guide/span.html#wp1079189

Regards,

Priyanka

[markwaltersccie]

Yes, for a Catalyst 9606 VSS pair v16.12.02 with span configured with source(s) and destination(s) which are on the different chassis, the span traffic is forwarded across the VSL link.  We just troubleshot significant drops on a 4x10Gbps VSL and a span was the cause.  In this case the span source was a range of vlans and the destination was a physical port on Chassis A.  The drops on the VSL were in the direction of Chassis B -> Chassis A.  Disabling the span immediately reduced bandwidth usage on the VSL and the drops ceased.  Cisco Live slide attached from: https://data.nag.wiki/Cisco/Datasheets/C9400/Catalyst_9000_Switching_Architecture.pdf