[c-nsp] Ethernet over MPLS xconnects on GSR 4-GE and 10GE SIP/SPA

Adam Chappell adam.chappell at gmail.com
Thu Nov 22 09:27:40 EST 2007


Hello all.

Does anyone have experience of the Ethernet over MPLS features when
running on the GSR?   I am having the devil's own time supporting
these features on some of our new POPs running with SPA-10GEv2.

Previously on 4x1GE and older code, configurations like the following
would be sufficent for me to provide an EoMPLS pseudowire to a
customer VLAN plucked off our metro Ethernet network.  The GSR would
happily transport frames from the VLAN straight onto the MPLS VC.

# Connect Gi0/0.100 to remote router 10.0.0.10 using VC 1234
int Gi0/0.100
encaps dot1q 100
xconnect 10.0.0.10 1234 encaps mpls

But starting in something like 12.0(28)S (and CSCsc21991), the GSR
gained the capabilities to look beyond the first VLAN tag so that it
could act on the customer tag to aid things like extract of an
Internet VLAN, efficient VLAN usage when build multi-VC topologies
etc. This takes the form of the "second-dot1q" command as a suffix to
the "encapsulation dot1q" line.

Unfortunately, in doing this the GSR also becomes non-transparent in
situations where the service provider simply wants to provide a
transparent Ethernet VC that may or may not carry VLAN tagged traffic.

For example, if I configure "encaps dot1q 100", it seems I can only
transport single tagged frames in VLAN 100 - not double tagged.  Yet
if I configure "encaps dot1q 100 second-dot1q any" I can only
transport double tags.

Has anyone else experienced this?  And if so, how have you worked
around it so that you are not sensitive to a customer's actual VLAN
setup?

-- Adam.


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