Query on EoMPLS

Unanswered Question
Nov 12th, 2007
User Badges:
  • Bronze, 100 points or more


I have a doubt in AToM Pseudowire.. I ve got a AToM pseudowire setup between my two PE routers with lastmile being on Ethernet sub-interfaces with VLAN tag on both the ends. I want to confirm while the packet traverses from PE1 to PE2, the VLAN tag (4 Bytes) will be carried over the packet i.e ( 1500+18+VLAN tag+ VC label+Tunnel label) .... Or PE1 will strip the VLAN tag and send the rest i.e (1500+18+VC label+Tunnel label)...

Thanks in advance

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Harold Ritter Mon, 11/12/2007 - 10:40
User Badges:
  • Cisco Employee,


In this scenario, the vlan tag is indeed carried as part of the pseudowire payload.


swaroop.potdar Mon, 11/12/2007 - 10:57
User Badges:
  • Blue, 1500 points or more

Arun, everything is transported with ATOM except Preamble, SFD, FCS.

Exlcuding these 3 everything from your SA/DA to your TPID (vlan info) is transported from Local to Remote PE.

Also the remote PE can overwrite the received Vlan info if configured to do so.

In your setup there shouldnt be any concern regarding the vlan tags.



manav.joshi Mon, 11/12/2007 - 23:30
User Badges:

In a pseudowire vlan is always carried forward from local PE to remote PE

The only issue to look at is that the interface over which the packet would get switched have the right mtu size

1500+18+VLAN tag+ VC label+Tunnel label+CW(optional)=1518+4+4+4+4(opt)=1534


for double-tag

1500+18+c-VLAN tag+s-VLAN tags + VC label+Tunnel label+CW(optional)= 1518+4+4+4+4+4(opt)= 1538

Hence, if you have not implemented MPLS TE

all interfaces should be able to pass 1500 MTU size payload with interfaces configured for 1542.


This Discussion