[c-nsp] Bizarre MPLS label problem, hex value?

[Nathan]

Hi,

I've tried all the MPLS troubleshooting docs I've been able to find,
and hard resets of BGP sessions, but I must be missing something.

I have four routers in a row, A B C D, I want packets to go inside a
VRF from A to D. Packets travel from B to D without any problem, but
not from A to D. My problem is general over all the VRFs I have
tested. I've chosen as example a vrf in which all the routers
concerned have interfaces (so they're all PE routers . . . that's not
a problem, is it?)

    A#sh ip cef vrf ${vrf} 0.0.0.0 0.0.0.0
    0.0.0.0/0, version 109, epoch 0, cached adjacency ${B as seen from A}
    0 packets, 0 bytes
      tag information set
        local tag: VPN-route-head
        fast tag rewrite with
            Recursive rewrite via ${D loopback} 0x20, tags imposed {413}
      via ${D loopback}, 0 dependencies, recursive
        next hop ${B as seen from A}, GigabitEthernet0/1.7 via ${D loopback}/32
        valid cached adjacency
        tag rewrite with
            Recursive rewrite via ${D loopback} 0x20, tags imposed {413}

What does that 0x20 mean??

I would have expected something like what I get when I try the same
diagnostics starting from router B :

    B#sh ip cef vrf ${vrf} 0.0.0.0 0.0.0.0
    0.0.0.0/0, version 105, epoch 0, cached adjacency ${C as seen from B}
    0 packets, 0 bytes
      tag information set
        local tag: VPN-route-head
        fast tag rewrite with Fa6/0, ${C as seen from B}, tags
imposed: {396 413}
      via ${D loopback}, 0 dependencies, recursive
        next hop ${C as seen from B}, FastEthernet6/0 via ${D loopback}/32
        valid cached adjacency
        tag rewrite with Fa6/0, ${C as seen from B}, tags imposed: {396 413}

    C#sh mpls forwarding-table labels 396
    Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
    tag    tag or VC   or Tunnel Id      switched   interface
    396    Pop tag     ${D loopback}/32   157406938041 Fa1/0      ${D
seen from C}

    D#sh mpls forwarding-table labels 413
    Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
    tag    tag or VC   or Tunnel Id      switched   interface
    413    Untagged    0.0.0.0/0[V]      1076956933 Fa0/0.12   192.168.12.4

If I understand correctly, the MPBGP session between A and D is
OK, but something is stopping A from learning the local tag on
B . . . the local tag that I would have expected to see instead of
VPN-route-head when I did the sh ip cef on B. The BGP sessions
between the two look OK :

    B#sh ip bgp ne ${A loopback} | b For address family: VPNv4 Unicast
     For address family: VPNv4 Unicast
      BGP table version 449551, neighbor version 449551
      Index 1, Offset 0, Mask 0x2
      peer-group-mpls peer-group member
                                     Sent       Rcvd
      Prefix activity:               ----       ----
        Prefixes Current:               0         59 (Consumes 3840 bytes)
        Prefixes Total:                88         59
        Implicit Withdraw:             88          0
        Explicit Withdraw:              0          0
        Used as bestpath:             n/a         60
        Used as multipath:            n/a          0

                                       Outbound    Inbound
      Local Policy Denied Prefixes:    --------    -------
        VPN Imported prefix:                 29        n/a
        Bestpath from this peer:             59        n/a
        Bestpath from iBGP peer:           2624        n/a
        Total:                             2712          0
      Number of NLRIs in the update sent: max 29, min 0

      Connections established 7; dropped 6
      Last reset 01:42:21, due to Peer closed the session
    Connection state is ESTAB, I/O status: 1, unread input bytes: 0

    A#sh ip bgp ne ${B loopback} | b For address family: VPNv4 Unicast
     For address family: VPNv4 Unicast
      BGP table version 419097, neighbor version 419097
      Index 1, Offset 0, Mask 0x2
      peer-group-mpls peer-group member
                                     Sent       Rcvd
      Prefix activity:               ----       ----
        Prefixes Current:              60         44 (Consumes 2816 bytes)
        Prefixes Total:                60         88
        Implicit Withdraw:             60         44
        Explicit Withdraw:              0          0
        Used as bestpath:             n/a         43
        Used as multipath:            n/a          0

                                       Outbound    Inbound
      Local Policy Denied Prefixes:    --------    -------
        Suppressed duplicate:                 0         44
        VPN Imported prefix:                 19        n/a
        Bestpath from this peer:              1        n/a
        Bestpath from iBGP peer:           2374        n/a
        Total:                             2394         44
      Number of NLRIs in the update sent: max 61, min 0

      Connections established 4; dropped 3
      Last reset 01:42:07, due to User reset

Can anybody explain what I should do? What that hex value is doing there?

Thanks,
-- 
Nathan