Switch behaving strange

Discussion in 'Cisco' started by Ajay, Feb 16, 2007.

  1. Ajay

    Ajay Guest

    In my catalyst 4506 switch some of the users loose their connectivity
    to the gateway in their pc for a certain period.If the ip is renwed in
    pc or the port is reseted in the switch then the pc will regain the
    reachabilty to the gateway.The lan connection is always showing
    connected even when it looses the reacability to gateway.The switching
    is running IOS 12.2(25)EWA7.I'm not seeing any loggs on switch also.
     
    Ajay, Feb 16, 2007
    #1
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  2. Ajay

    Thrill5 Guest

    If the switch is also the default gateway and you are running HSRP this
    could be an ARP/CAM timeout problem. The issue is that the timeouts for the
    ARP entries (on the routing side) and the CAM entries (on the switching
    side) are different. The default CAM timeout for the MAC address is 10
    minutes and the ARP entries is something like 60 minutes. The fix is to
    make them both the same. We change the ARP time to 10 minutes and this can
    be done using the command "arp timeout 300" on each VLAN interface. I don't
    know why Cisco doesn't make them the same by default. Resetting the port on
    the switch or renewing the IP on the client forces the switch to relearn the
    MAC in the CAM table. By setting the ARP timeout to same value as the CAM
    timeout, the routing side will ARP the address of the client which will have
    the side effect of the switching side to relearning the MAC in the CAM
    table.

    You can verify this is your problem if pinging the IP of the client from the
    switch (or pinging the default gateway from the client, I can't remember
    which) also temporarily fixes the problem.

    Scott
     
    Thrill5, Feb 16, 2007
    #2
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