[c-nsp] Mpls with layer-2 in between

Shawn L shawn at rmrf.us
Mon Oct 12 14:34:52 EDT 2020

I have kind of a strange situation.  Trying to figure out what to do moving
forward, and not sure what the best (or quickest) way to solve the issue.

I have a mpls cross-connect (pseudowire) between 2 sites.  The link comes
up, but I can't pass any traffic.

sh mpls l2transport vc - shows the connection is up
ping mpls pseudowire x.x.x.x YY reply mode ipv4 - gives me a time-out.

The link goes from an ASR920 - Cisco 3850 ------- Cisco 3850 - ASR920

The long dashed line is a 40-gig layer-2 link between the 2 Cisco 3850
switches.  Both switches run eigrp and terminate mpls links just fine; ie

interface TenGigabitEthernet1/0/4
 no switchport
 ip address
 mpls ip
 mpls label protocol ldp

ASR920 ---- 3850 ---- ASR920 pseudowires work fine.  It's an issue when the
2nd 3850 comes into the mix.

When I do a traceroute from end-to-end, I see the vlan 1 interface of the
3850, not the loopback interface.  So, I'm guessing it's taking the layer-2
path instead of using the loopback interfaces and routing it.

The best way to fix it is to remove the 3850s from the equation and put in
real routers.  Unfortunately that means I can't utilize the 40 gig link to
the other site.

Is it possible to have a layer-2 connection in-between 2 mpls speaking
routers?  ie

ASR920 --- 'new' router --- 3850--------3850 -- 'new' router ---- ASR920

Or, is there a way to tell the 3850s to route the connection instead of
switch it (and not break switching on them)?


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