Pseudowire hairpin

[jschmied]

We are working with an ASR9010 with XR 4.2.3 and have a l2vpn pseudwire configured to a single remote location. Works as expected. We want to add a second pseudowire from the ASR9010 to a 2nd remote location. The setup requires that the second location be able to communicate with both the main site connected to the ASR and the remote location on the first psuedowire. Can the remote locations communicate with each other through the pseudowires back to the ASR at the main site with a configuration such as this;

l2vpn
 !
 bridge group L2-Group
  bridge-domain L2-Domain

   !
   interface GigabitEthernet0/0/0/0.100
   !
   neighbor 10.1.1.1 pw-id 100
   !
   neighbor 10.2.2.1 pw-id 100
   !
!

The pseudowires terminate to Cisco 7600's with IOS.

Thanks,

Jamie

[Akash Agrawal]

Hi Jamie,

Can we consider option of configuring VPLS instead of two point to point xconnect. If we have some restriction and want to continue with xconnect only, then routing to be involved on main site to have communication between two remote locations.

VPLS reference guide

http://www.cisco.com/en/US/docs/routers/asr9000/software/mpls/configuration/guide/gcasr9kvpls.html#wp1148290

Sample config

RP/0/RSP0/CPU0:router1#sh run l2vpn bridge group customer1

l2vpn

 bridge group customer1

  bridge-domain finance

   interface GigabitEthernet0/1/0/3.3

   !

   vfi customer1-finance

    neighbor 10.0.0.12 pw-id 3

    !

    neighbor 10.0.0.13 pw-id 3

    !

    neighbor 10.0.0.14 pw-id 3

    !

   !

  !

Regards,

Akash

[jschmied]

Akash - Thank you very much for your response. Is the function of the VFI to provide forwarding between the pseudowires?

Jamie

[Akash Agrawal]

VPLS (VFI) to be configured on all three nodes and then mpls backbone will act as virtual switch and then any site can talk to other side like they are connected to a switch. Each PE will also do MAC learning and based on MAC will forward traffic to correct destination site.

Akash 

[jschmied]

The remote routers are 7600's with IOS. Will they support the VFI configuration?

[xthuijs]

the config that you're after is a standard hub and spoke model, this is very fine.

the gotcha is here with the VFI and the pw definition.

What a VFI does is it puts those circuits in the same split horizon group. this means that a packet received on a circuit inside the VFI will never be forwarded out ANY circuit in that same VFI/split horizon group.

So if site 1 is the hub, and site 2 and 3 are the spokes, and site 2 wants to speak with 3, it needs to go via the hub, pw in and pw out.

so putting the pw's in a VFI is here not what you want to do, you could configure the PW's just as regular "attachment circuits" i the same hierarchy as the gig interface.

mac learning will forward the packet from PW to PW.

xander

[jschmied]

Xander - Would the configuration in the first post be the correct config for our requirements then?

l2vpn
 !
 bridge group L2-Group
  bridge-domain L2-Domain

   !
   interface GigabitEthernet0/0/0/0.100
   !
   neighbor 10.1.1.1 pw-id 100
   !
   neighbor 10.2.2.1 pw-id 100
   !
!

Where 10.1.1.1 and 10.2.2.1 are remote Cisco 7600 routers and the hub with this config is an ASR9010.

Thanks for your comments!

Jamie

[xthuijs · Accepted solution]

correct indeed, that is the right config for this model.

note that if you every decide to make a pw between the 7600's then you will need to move them to vfi's, otherwise you'll get a meltdown since it is then one big loop obviously...

If you like to understand VFI's a bit better and the split horizon stuff, I hope this article I wrote may help with that: https://supportforums.cisco.com/document/61401/asr9000xr-using-mst-ag-mst-access-gateway-mst-and-vpls

cheers!

xander

[jschmied]

Xander, Akash,

We implemented the configuration this morning and everything worked great! Thanks for your help with this.

Jamie

[xthuijs]

Superb Jamie! thanks for letting us know it worked like a charm!!

cheers

xander