Address bound to LDP peer in LDP show cmd

Hi Everyone 

 

Hitting my head to understand this basic stuff in LDP

Why is the ip add of all the interface enabled in mpls of the adj LDP peer is adv/seen in the LDP info

 

EG:

new-york#show mpls ldp neighbor detail

Peer LDP Ident: 10.200.254.2:0; Local LDP Ident 10.200.254.1:0

TCP connection: 10.200.254.2.646 - 10.200.255.1.64481

State: Oper; Msgs sent/rcvd: 1303/1289; Downstream; Last TIB rev sent 743

Up time: 17:20:24; UID: 101; Peer Id 0;

LDP discovery sources:

Ethernet1/1; Src IP addr: 10.200.210.2

holdtime: 15000 ms, hello interval: 5000 ms

Ethernet1/2; Src IP addr: 10.200.218.2

holdtime: 15000 ms, hello interval: 5000 ms

Addresses bound to peer LDP Ident:

10.200.254.2 10.200.210.2 10.200.218.2 10.200.211.1

10.200.215.1

Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab

 

Why do we need these other interface ip address of the adj ldp peer.?

 

Hoping someone can clarify

 

Thanks in Advance for the Reply

Comments

  • Check your LFIB, you got labels assigned to all of them?

  • These are the addresses bound to your LDP/TDP peer, you should have labels for all of those in your LFIB, try sh mpls forwarding and check it out :)

  • Think of how LDP label advertisements are made up:

    The advertisement consists of an LDP Identifier, plus a label. To see the advertisements that a neighbor sent you, you could do something like this:

    Let say that we want to see the labels we have received for 37.3.3.3/32

     

    R4#sh mpls ldp bindings 37.3.3.3 32 

      lib entry: 37.3.3.3/32, rev 83

            local binding:  label: 30

            remote binding: lsr: 1.1.1.1:0, label: 26  --> only LDP-ID plus label

            remote binding: lsr: 5.5.5.5:0, label: 30  --> only LDP-ID plus label

     

    Now we know the labels that both R1 (LDP ID 1.1.1.1) and R5 (LDP ID 5.5.5.5) are advertising to us for that prefix. Looking at the advertisement, you can see that we are only informed of an LDP ID plus a label. 

     

    Next we need to see how we are routing to get to 37.3.3.3/32. This will determine what the downstream LSR is and will populate the LFIB. 

     

    R4#show ip route 37.3.3.3

    Routing entry for 37.3.3.3/32

      Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 10

      Last update from 10.1.14.1 on Ethernet1/1, 00:02:45 ago

      Routing Descriptor Blocks:

      * 10.1.14.1, from 1.1.1.1, 00:02:51 ago, via Ethernet1/1

          Route metric is 20, traffic share count is 1

     

    How can the router map this interface IP address (the next hop, 10.1.14.1) to a label advertisment? All that the LDP advertisment told us was the label and LDP-ID, but it did not tell us the connected interfaces on that router. 

     

    In order to make this "mapping", the router looks at the interfaces advertised by LDP peer in the "Address" messages. You can see these here:

     

    R4#show mpls ldp neighbor 1.1.1.1

        Peer LDP Ident: 1.1.1.1:0; Local LDP Ident 4.4.4.4:0

            TCP connection: 1.1.1.1.646 - 4.4.4.4.57436

            State: Oper; Msgs sent/rcvd: 1162/1151; Downstream

            Up time: 15:54:59

            LDP discovery sources:

              Ethernet1/1, Src IP addr: 10.1.14.1

            Addresses bound to peer LDP Ident:

              10.1.13.1       10.1.14.1       10.1.12.1       1.1.1.1  

     

     

    This is how R4 is able to connecte the received label, to the received route.  It looks to see what LDP peer (LDP-ID) has the 10.1.14.1 address advertised as "bound". It finds that 1.1.1.1 has it, so it uses the label advertised by 1.1.1.1. The result is a populated LFIB.

     

    R4#show mpls forwarding-table 37.3.3.3 32 

    Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    

    Label      Label      or Tunnel Id     Switched      interface              

    30         26         37.3.3.3/32      0             Et1/1      10.1.14.1 

     

     

    If we did not have these "bound addresses", the router would have no way of making a connection (or mapping) between the received labels and the routes. 

     

    Hope this helps!

     

    Pablo

     

     

  • If we did not have these "bound addresses", the router would have no way of making a connection (or mapping) between the received labels and the routes. 

     

    Hope this helps!

     

    Pablo

     

    That was a fantastic explanation sir!

    -Warjack

Sign In or Register to comment.