Inter-AS L2VPN MPLS Solutions

  • Option A:
    • each SP treats the other as CE
    • PW terminates as ASBR.
    • The link between ASBR is a AC instead of a PW
    • Granular QoS control between ASBR
  • Option B:
    • PE and P LSR do not learn remote PW endpoint addresses
    • Only the IP for PW endpoint (LER) that are ASBR leaked between ASs
    • T-LDP between ASBR of the SPs
    • PW terminates at ASBR. ASBR in turn build a new PW to its peer ASBR. This new PW connects the original PWs together
  • Option C:
    • PE loopback prefix and labels are exchange between two AS using MP-eBGP on ASBR
    • Instead of terminate the PW on its own ASBR, the PW is terminated on the remote PE on another AS. In another word, the PW is extended end to end between the two ASes
  • Summary:
    • All Inter-AS models (A,B,C) are supported to carry VPWS or VPLS PWs
    • IOS supports LDP for signaling, BGP for Auto-discovery (VPLS)
    • IOS XR supports both LDP and BGP signaling
    • Option B is not supported for BGP signal PWs
    • Per-PW QoS is not support
    • AC interworking is supported in IOS XR
    • L2VPN over TE or GRE is supported


  1. nik

    What is the exact meaning of “Option B is not supported for BGP signal PWs” can you please explain more ?

    • Ken Yeo

      I believe when L2VPN was initially introduced for Inter-AS Option B, only LDP signaling was supported, BGP was only used for auto-discovery. However later on BGP signaling was added as a feature. See

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