ASR 9000, spanning tree and access ports

[Simon Bonham]

Hi there,

I have been busy with a migration for a customer, from a pair of 7600's to the ASR 9000. What I am struggling with is the L2 side of things and spanning tree. I have setup all the necessary trunks, bridge domains, BVI's etc and everything seems to work okay except when it comes to access ports.

If I have for example a standard access port on the 7600, I migrate it to the ASR9000 as follows:

interface GigabitEthernet0/1/0/11.390 l2transport
 encapsulation untagged
!

The BVI is configured like so:

!
interface BVI390
description Server
ipv4 address 10.0.0.1 255.255.255.0
!

I then configure it on the L2 VPN side...

!
l2vpn
  bridge-domain VLAN390
   interface Bundle-Ether1.390
   !
   interface GigabitEthernet0/1/0/11.390
   !
   routed interface BVI390
  !

I can then ping the server hanging off Gi0/1/0/11...

RP/0/RSP0/CPU0:asr9k#ping 10.0.0.20          
Tue Oct 20 11:57:48.773 UTC
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.20, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

But as soon as I add the port to the spanning tree instance, it just locks up and it no longer works? I realise in this case its a server that's attached and doesn't really need spanning tree, but I would have thought I needed to add the port to spanning tree like in the case of the 7600.

spanning-tree pvrst PVRSTPNRK01
!
vlan 390
  priority 4096

!
interface GigabitEthernet0/1/0/11  ! If this is configured then the port stops working.
!

Please help me understand what I should be adding to the spanning tree topology??

The STP topology is simple. Two ASR9K's with a trunk (Bundle-Ether and sub-ints) between them, and then an additional L2 switch connected to both ASR9K's with trunks as well. ASR9K on the left is root bridge.

ASR9K  ---------------- ASR9K

      \                              /

         \                        /

             \               /

             L2 Switch

[Aleksandar Vidakovic]

hi Simon,

can you look for some clues in the "sh spanning-tree pvrst PVRSTPNRK01 ..." commands output?

Does it work if you change the encap on the Gig0/1/0/11.390?

regards,

/Aleksandar

[Bryan Garland]

Simon,

It would seem like you have an untagged and tagged interface in the same BD.  This won't work when trying to run spanningtree on both.  This will make the last one added shutdown (from l2vpn perspective) due to an MSTi mismatch.  Untagged interfaces don't have a "vlan" tag associated and therefore use an MSTi of 0.  So when using spanning tree here, we shouldn't mix tagged and untagged.  

So to your design here.  I see it's an l2 switch connected to the A9ks.  Can you change that to a trunk/tagged interface?  That should resolve your problem.

Thanks,

Bryan