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  • 1.  MPLS L3vpn traceroute question

    Posted 07-23-2023 01:22

    I have a following topology

    CE1  ---->PE1 ------->RR------>PE2 ----->CE2
    on PE2

    root@Demo-LS# show logical-systems PE2 | display set    
    set logical-systems PE2 interfaces ge-0/0/2 unit 10
    set logical-systems PE2 interfaces lo0 unit 12
    set logical-systems PE2 protocols mpls icmp-tunneling
    set logical-systems PE2 protocols mpls interface ge-0/0/2.10
    set logical-systems PE2 protocols bgp group To-mccr-hmb-1 type internal
    set logical-systems PE2 protocols bgp group To-mccr-hmb-1 local-address 10.50.0.4
    set logical-systems PE2 protocols bgp group To-mccr-hmb-1 family inet unicast
    set logical-systems PE2 protocols bgp group To-mccr-hmb-1 family inet-vpn unicast
    set logical-systems PE2 protocols bgp group To-mccr-hmb-1 neighbor 10.50.0.2
    set logical-systems PE2 protocols ospf area 0.0.0.0 interface ge-0/0/2.10 interface-type p2p
    set logical-systems PE2 protocols ospf area 0.0.0.0 interface lo0.12 passive
    set logical-systems PE2 protocols ldp interface ge-0/0/2.10
    set logical-systems PE2 protocols ldp interface lo0.12
    set logical-systems PE2 routing-instances MC instance-type vrf
    set logical-systems PE2 routing-instances MC interface lt-0/0/10.2
    set logical-systems PE2 routing-instances MC route-distinguisher 10.50.0.4:2
    set logical-systems PE2 routing-instances MC vrf-target target:64850:64850
    set logical-systems PE2 routing-instances MC vrf-table-label
    set logical-systems PE2 routing-instances MC protocols bgp group To-SeattlePC neighbor 10.50.20.11 peer-as 64890
    set logical-systems PE2 routing-options router-id 10.50.0.4
    set logical-systems PE2 routing-options autonomous-system 64850
    
    [edit]
    root@Demo-LS# show interfaces ge-0/0/2.10 | display set        
    set interfaces ge-0/0/2 unit 10 vlan-id 10
    set interfaces ge-0/0/2 unit 10 family inet address 10.50.0.73/31
    set interfaces ge-0/0/2 unit 10 family mpls
    
    [edit]
    root@Demo-LS# show interfaces lt-0/0/10.2 | display set        
    set interfaces lt-0/0/10 unit 2 encapsulation ethernet
    set interfaces lt-0/0/10 unit 2 peer-unit 3
    set interfaces lt-0/0/10 unit 2 family inet address 10.50.20.10/31
    set interfaces lt-0/0/10 unit 2 family mpls

    From CE2, traceroute as follows:

    root@Demo-LS# run traceroute 140.142.251.100 logical-system SeattlePC   
    traceroute to 140.142.251.100 (140.142.251.100), 30 hops max, 40 byte packets
     1  10.50.20.10 (10.50.20.10)  4.175 ms  2.297 ms  1.425 ms                            PE2
     2  10.50.0.72 (10.50.0.72)  8.077 ms  6.461 ms  4.669 ms                                  RR
         MPLS Label=299792 CoS=0 TTL=1 S=0
         MPLS Label=16 CoS=0 TTL=1 S=1
     3  10.51.10.1 (10.51.10.1)  6.737 ms  4.706 ms  7.543 ms                                  PE1    (why no label shown for this line)
     4  10.51.10.0 (10.51.10.0)  81.372 ms  142.349 ms  141.163 ms
     5  140.142.251.100 (140.142.251.100)  186.980 ms  127.329 ms  140.676 ms

    From CE1, I did  traceroute to the following:

    root@TDC-LS> traceroute 140.142.41.100 source 140.142.251.100 logical-system CFW      
    traceroute to 140.142.41.100 (140.142.41.100) from 140.142.251.100, 30 hops max, 40 byte packets
     1  140.142.27.195 (140.142.27.195)  113.023 ms  160.165 ms  165.151 ms
     2  10.51.10.1 (10.51.10.1)  163.937 ms  160.708 ms  162.757 ms                               10.51.10.1 is PE1
     3  10.50.0.94 (10.50.0.94)  164.166 ms  164.309 ms  161.976 ms                               10.50.0.94 is RR
         MPLS Label=299776 CoS=0 TTL=1 S=0
         MPLS Label=16 CoS=0 TTL=1 S=1
     4  10.50.20.10 (10.50.20.10)  169.344 ms  167.168 ms  161.481 ms                        10.50.20.10 is in VRF on PE2
     5  140.142.41.100 (140.142.41.100)  166.046 ms  162.767 ms  164.566 ms

    I do not understand Line 4. I expect to see  10.50.0.73. not 10.50.20.10 which is used in the vrf to peer with CE2.

    I had the same topology in other lab, I got the following:

    root@CE1# run traceroute 10.12.1.2 logical-system JCust-1

    traceroute to 10.12.1.2 (10.12.1.2), 30 hops max, 40 byte packets

     1  10.11.1.1 (10.11.1.1)  187.381 ms  1.907 ms  1.777 ms

     2  172.16.1.2 (172.16.1.2)  307.530 ms  10.823 ms  6.122 ms

         MPLS Label=299776 CoS=0 TTL=1 S=0

         MPLS Label=299792 CoS=0 TTL=1 S=1

     3  172.16.2.1 (172.16.2.1)  4.974 ms  6.760 ms  4.366 ms

         MPLS Label=299792 CoS=0 TTL=1 S=1

     4  10.12.1.2 (10.12.1.2)  6.080 ms  6.715 ms  6.685 ms

     

     What have I missed ?

    thanks a lot in advance !!



  • 2.  RE: MPLS L3vpn traceroute question

    Posted 07-23-2023 12:35

    I noticed it is related which IP the device selects to response traceroute packet.  trying to find the information on this.




  • 3.  RE: MPLS L3vpn traceroute question

    Posted 07-23-2023 13:26

    Based on my understanding, normally 

    the receiving device will send an ICMP message "TTL Expired" from the interface that received that packet.

    But I did see the loopback IP responses traceroute packets.

    when does a device select other IP to response traceroute packets ?

    thanks !!