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Forum Replies

  1. milan9 says:

    Great as always. Just one minor issue. On the first topology picture, shouldnt the provider AS number be 123 as you stated in text instead of AS 234 or vice versa?

  2. Marek,
    This topic can become less confusing if you think about what is going on in the control plane vs the data plane. The RTs are used in the control plane to associate ROUTES with VRFs. The VPN label is used in the data plane to associate PACKETS with VRFs.

    Check out this great article that talks about why RDs, RTs, and VPN Labels are all needed:

  3. Dear Rene,,
    I have encountered following log message when setting this up. Can you confirm if we need to make the Loopback Interfaces as /32 s across the MPLS core ?

    *Jan 15 01:49:04.853: %BGP-4-VPNV4NH_MASK: Nexthop may not be reachable from neigbor - not /32 mask

  4. This error occurs if you have a loopback interface with a subnet mask that is not /32 and that is advertised in OSPF.

    OSPF will always advertise a loopback as a /32 (network type LOOPBACK). LDP however, looks at the actual subnet mask of the interface so there will be a mismatch between LDP and your routing table.

    To fix this, you have two options:

    • Change the network type of your loopback interface to ip ospf network-point-to-point so that OSPF advertises the actual subnet mask of the interface.


    • Change the subnet mask of the loopback interface to /32.


  5. Hi Rene,
    When we give a trace from a Non-MPLS device and its travel thru a MPLS network.So, how Device know about the MPLS path IP and label from output ..

    CE1#traceroute source loopback 0
    Type escape sequence to abort.
    Tracing the route to
    VRF info: (vrf in name/id, vrf out name/id)
      1 0 msec 0 msec 4 msec
      **2 [MPLS: Labels 17/19 Exp 0] 0 msec 0 msec 4 msec**
      **3 [MPLS: Label 19 Exp 0] 0 msec 0 msec 4 msec**
      4 0 msec 0 msec *

    So from the output how CE1 informed the IP and with the label value 17 , 19 respectively.I want to know the discovering process deeply. please assist me in your clear text .Thx

    I know how Traceroute works normally but In MPLS domain I cant understand .


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