LDP behaviour. weird or expected?

I have the following scenario -

R1(s1/1)------12.x-------------(s1/0.1)R2(s1/0.2)------------25.x------------(s1/0)R5

R1:

interface Serial1/1
 ip address 150.1.12.1 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-point
 mpls ip
 frame-relay map ip 150.1.12.2 102 broadcast
end

R2:

interface Serial1/0.1 point-to-point
 ip address 150.1.12.2 255.255.255.0
 mpls ip
 frame-relay interface-dlci 201
interface Serial1/0.2 point-to-point
 ip address 150.1.25.2 255.255.255.0
 mpls ip
 frame-relay interface-dlci 205

R5:

interface Serial1/0
 ip address 150.1.25.5 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-point
 mpls ip
 serial restart-delay 0
 frame-relay map ip 150.1.25.2 502 broadcast
end

Now. I see there is ldp session established directly between R1 and R5. I thought ldp session are created over directly connected  neighbors. What explains this behaviour ?

R1#show mpls ldp neighbor
    Peer LDP Ident: 150.1.13.3:0; Local LDP Ident 150.1.13.1:0
        TCP connection: 150.1.13.3.56709 - 150.1.13.1.646
        State: Oper; Msgs sent/rcvd: 96/94; Downstream
        Up time: 01:07:46
        LDP discovery sources:
          Serial1/0, Src IP addr: 150.1.13.3
        Addresses bound to peer LDP Ident:
          150.1.13.3      150.1.3.3
    Peer LDP Ident: 150.1.25.2:0; Local LDP Ident 150.1.13.1:0
        TCP connection: 150.1.25.2.57282 - 150.1.13.1.646
        State: Oper; Msgs sent/rcvd: 35/35; Downstream
        Up time: 00:20:26
        LDP discovery sources:
          Serial1/1, Src IP addr: 150.1.12.2
        Addresses bound to peer LDP Ident:
          150.1.12.2      150.1.25.2      150.1.2.2
    Peer LDP Ident: 150.1.25.5:0; Local LDP Ident 150.1.13.1:0
        TCP connection: 150.1.25.5.48447 - 150.1.13.1.646
        State: Oper; Msgs sent/rcvd: 34/34; Downstream
        Up time: 00:19:59
        LDP discovery sources:
          Serial1/1, Src IP addr: 150.1.25.5
        Addresses bound to peer LDP Ident:
          150.1.25.5      150.1.56.5      150.1.5.5

 

 

Comments

  • Can you ping 224.0.0.2 from R1 and then from R5 and see who replies?  Also are there any FR DLCIs between R1 and R5 as I noticed you didn't have FR inverse-ARP disabled and are using the physical interfaces.

    -- 
    Brian Dennis, CCIEx5 #2210 (R&S/ISP-Dial/Security/SP/Voice)

    INE, Inc.

    From: kar_sagar28 <[email protected]>
    Reply-To: "[email protected]" <[email protected]>
    Date: Wednesday, February 27, 2013 10:15 AM
    To: Brian Dennis <[email protected]>
    Subject: [CCIE R&S] LDP behaviour. weird or expected?

    I have the following scenario -

    R1(s1/1)------12.x-------------(s1/0.1)R2(s1/0.2)------------25.x------------(s1/0)R5

    R1:

    interface Serial1/1
     ip address 150.1.12.1 255.255.255.0
     encapsulation frame-relay
     ip ospf network point-to-point
     mpls ip
     frame-relay map ip 150.1.12.2 102 broadcast
    end

    R2:

    interface Serial1/0.1 point-to-point
     ip address 150.1.12.2 255.255.255.0
     mpls ip
     frame-relay interface-dlci 201
    interface Serial1/0.2 point-to-point
     ip address 150.1.25.2 255.255.255.0
     mpls ip
     frame-relay interface-dlci 205

    R5:

    interface Serial1/0
     ip address 150.1.25.5 255.255.255.0
     encapsulation frame-relay
     ip ospf network point-to-point
     mpls ip
     serial restart-delay 0
     frame-relay map ip 150.1.25.2 502 broadcast
    end

    Now. I see there is ldp session established directly between R1 and R5. I thought ldp session are created over directly connected  neighbors. What explains this behaviour ?

    R1#show mpls ldp neighbor
        Peer LDP Ident: 150.1.13.3:0; Local LDP Ident 150.1.13.1:0
            TCP connection: 150.1.13.3.56709 - 150.1.13.1.646
            State: Oper; Msgs sent/rcvd: 96/94; Downstream
            Up time: 01:07:46
            LDP discovery sources:
              Serial1/0, Src IP addr: 150.1.13.3
            Addresses bound to peer LDP Ident:
              150.1.13.3      150.1.3.3
        Peer LDP Ident: 150.1.25.2:0; Local LDP Ident 150.1.13.1:0
            TCP connection: 150.1.25.2.57282 - 150.1.13.1.646
            State: Oper; Msgs sent/rcvd: 35/35; Downstream
            Up time: 00:20:26
            LDP discovery sources:
              Serial1/1, Src IP addr: 150.1.12.2
            Addresses bound to peer LDP Ident:
              150.1.12.2      150.1.25.2      150.1.2.2
        Peer LDP Ident: 150.1.25.5:0; Local LDP Ident 150.1.13.1:0
            TCP connection: 150.1.25.5.48447 - 150.1.13.1.646
            State: Oper; Msgs sent/rcvd: 34/34; Downstream
            Up time: 00:19:59
            LDP discovery sources:
              Serial1/1, Src IP addr: 150.1.25.5
            Addresses bound to peer LDP Ident:
              150.1.25.5      150.1.56.5      150.1.5.5

     

     




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  • Thanks Brian! I did the section again with inverse-arp disabed and it solved the issue.

     

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