problems with serial line to ISP w/ CEF

Discussion in 'Cisco' started by Warren J. Beckett, Oct 19, 2004.

  1. Hi,

    I have a serial (g703) link to an ISP that is giving me brief. It has
    just been installed and not yet in production.

    The serial interface is configured as a half-bridge, and I also NAT
    outside on it as well. Both the serial networks work,but when I enable
    CEF the serial interface the connection ISP fails.

    The routers is a 3620 (C3620-IS-M), Version 12.0(7)T3, RELEASE SOFTWARE

    Here is the serial interface:

    interface Serial0/1:0
    description Connection to Lefkosa
    bandwidth 1984
    ip address
    ip access-group Ext_IN in
    no ip unreachables
    no ip directed-broadcast
    ip nat outside
    encapsulation ppp
    ip mroute-cache
    no cdp enable
    ppp bridge ip

    The problem seems to stem from this:
    IP Serial0/1:0 point2point(8) (incomplete)

    The IP address of the other end of the like is, and appears
    in the ARP table: But with CEF enable I am un able to ping it.
    Internet 0 000c.4203.1b69 ARPA Serial0/1:0

    Serial0/1:0 is up (if_number 7)
    Internet address is
    ICMP redirects are always sent
    Per packet loadbalancing is disabled
    IP unicast RPF check is disabled
    Inbound access list is 0
    Outbound access list is not set
    IP policy routing is disabled
    Interface is marked as point to point interface
    Hardware idb is Serial0/1:0
    Fast switching type 7, interface type 13
    IP CEF switching enabled
    IP CEF Feature Fast switching turbo vector
    Input fast flags 0x61, Output fast flags 0x100
    ifindex 6(6)
    Slot 0 Slot unit 1 VC 0
    Transmit limit accumulator 0x0 (0x0)
    IP MTU 1500

    With CEF enable I am unable to ping it from the router, but I can ping
    it from the inside network but get a 50% packet loss.

    I also get this message in the syslog

    Oct 19 13:46:05 12410: 01:06:27: CEF-Drop: Packet for -- encapsulation
    Oct 19 13:46:07 12411: 01:06:29: CEF-Drop: Stalled adjacency
    for on Serial0/1:0 for destination 217.

    Any ideas why CEF fails to form an adjacency with the other end of the
    PPP link? and why it works ok without CEF enabled.

    Any help would be appreciated.


    Warren J. Beckett, Oct 19, 2004
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