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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:
    https://mellowd.co.uk/ccie/?p=2923

  3. 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.

    OR

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

    Rene

  4. Hello Mohammad

    An excellent and very in depth explanation of how traceroute and MPLS function can be found in this Cisco documentation. It includes information about the elements found within the frame headers and how these are translated and outputted in the traceroute output as label values.

    I hope this has been helpful!

    Laz

  5. Hi Rene,
    Please see the bold output below …

    CE1#traceroute 5.5.5.5 source loopback 0
    Type escape sequence to abort.
    Tracing the route to 5.5.5.5
    VRF info: (vrf in name/id, vrf out name/id)
      1 192.168.12.2 0 msec 0 msec 4 msec
      2 192.168.23.3 [MPLS: Labels 17/19 Exp 0] 0 msec 0 msec 4 msec
      **3 192.168.45.4 [MPLS: Label 19 Exp 0] 0 msec 0 msec 4 msec**
      4 192.168.45.5 0 msec 0 msec *
    

    why its showing 192.168.45.4 instead of 192.168.34.4 . As we know it should show exit interface IP . Is there logic behind this ??? Please make me clear .Thx

    br//zaman

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