Multicast broadcast traffic forwarding to wrong interface

Discussion in 'Cisco' started by markb@1e.com, Jul 11, 2007.

  1. Guest

    I have a simple 2 router back-to-back serial setup with a LAN on each
    end. Each router has 1 FastEthernet interface and 2 Serial.

    I have multicast enabled and pim set to dense mode.

    I have a client sending a MADCAP discover packet to find a server - on
    the same LAN this works fine. If I move the client to the remote
    subnet it fails.

    On the router at the client end I see the following MROUTE output for
    239.255.255.254 (the standard MADCAP discover address)

    (*, 239.255.255.254), 02:42:00/stopped, RP 0.0.0.0, flags: D
    Incoming interface: Null, RPF nbr 0.0.0.0
    Outgoing interface list:
    Serial1, Forward/Dense, 02:41:59/00:00:00
    Serial0, Forward/Dense, 02:42:00/00:00:00

    and for the client address (192.168.101.23) I see this entry

    (192.168.101.23, 239.255.255.254), 02:41:00/00:01:49, flags: T
    Incoming interface: FastEthernet0, RPF nbr 0.0.0.0
    Outgoing interface list:
    Serial0, Forward/Dense, 02:41:00/00:00:00
    Serial1, Forward/Dense, 02:41:00/00:00:00

    that router also shows this PIM routing table
    PIM Neighbor Table
    Neighbor Interface Uptime/Expires Ver DR
    Address Prio/Mode
    192.168.12.1 Serial1 03:02:27/00:01:35 v2 1 / S

    the other end of the serial link I see this PIM routing table

    PIM Neighbor Table
    Neighbor Interface Uptime/Expires Ver DR
    Address Prio/Mode
    192.168.12.2 Serial1 03:03:52/00:01:27 v2 1 / S

    so PIM is happy for the intra router link.

    on the server end router I see the following MROUTE info for
    239.255.255.254

    (*, 239.255.255.254), 02:43:38/stopped, RP 0.0.0.0, flags: D
    Incoming interface: Null, RPF nbr 0.0.0.0
    Outgoing interface list:
    Serial1, Forward/Dense, 02:43:38/00:00:00
    Serial0, Forward/Dense, 02:43:38/00:00:00

    and for the client entry I see

    (192.168.101.23, 239.255.255.254), 02:43:39/00:01:40, flags: T
    Incoming interface: Serial1, RPF nbr 192.168.12.2
    Outgoing interface list:
    Serial0, Forward/Dense, 02:43:39/00:00:00

    So it appears that the multicast packets are being routed out of
    Serial0, but the server is on FastEthernet0.

    Why doesn't FastEthernet0 appear on the MROUTE for 239.255.255.254
    when it does for some other group addresses on the same router?

    (e.g.

    (*, 239.0.9.0), 02:45:25/00:02:41, RP 0.0.0.0, flags: DC
    Incoming interface: Null, RPF nbr 0.0.0.0
    Outgoing interface list:
    Serial1, Forward/Dense, 02:45:25/00:00:00
    Serial0, Forward/Dense, 02:45:25/00:00:00
    FastEthernet0, Forward/Dense, 02:45:25/00:00:00

    )

    Thanks,

    Mark.
    , Jul 11, 2007
    #1
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