Do you need LDP with MPLS TE?

An anonymous commenter to my implicit NULL/PHP post made a very valid point:

Most Cisco documentation states that you must enable LDP before doing MPLS-TE, which is a complete fallacy.

If you're using MPLS TE simply to shift IP traffic around your network, he's absolutely right: there is no need to run LDP if you have an IP-only network. If you're running MPLS VPN or BGP on edges/MPLS in the core, the answer becomes “it depends.” The detailed rules and undesired side effects if you ignore them are summarized in the MPLS Traffic Engineering in MPLS VPN environment article.

Read the article in CT3 wiki.

4 comments:

  1. Does this mean it is possible to do MPLS TE in an IP only net work aslong as you are doing the tunnels between PEs, and BGP on the PEs only? and if you have full/partial mesh of MPLS TE Tunnels can you also do MPLS VPN on an IP only network?

    Your graphics are nice, but it would be verry nice to see some config examples as well.

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  2. @Justin:

    "Does this mean it is possible to do MPLS TE in an IP only net work aslong as you are doing the tunnels between PEs, and BGP on the PEs only?"

    In theory yes, but if your tunnels break down for any reason (for example, the tunnel could not be established due to insufficient free bandwidth), your transit traffic would be blackholed.

    "if you have full/partial mesh of MPLS TE Tunnels can you also do MPLS VPN on an IP only network?"

    Yes ... with the same caveats as above.

    "Your graphics are nice, but it would be verry nice to see some config examples as well."

    I'll do the MPLS/VPN over IP network setup and post the results.

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  3. Precisely. Great write up. If the network is designed properly, you should never need LDP. There are a few knobs to consider if you are running a multi-vendor TE domain. Not sure if there is interest in that on this blog, though.

    ReplyDelete
  4. @Anonymous: Please send me the knobs (you can use this form).

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.