Question on limit to dynamically learned MAC addresses per vlan

Discussion in 'Cisco' started by pfisterfarm, Jan 26, 2010.

  1. pfisterfarm

    pfisterfarm Guest

    I'm trying to troubleshoot connectivity problems between a virtual
    server at a central site and PCs in the same vlan at a remote site. At
    the central site is several VMWare servers connected to a 3560 switch.
    The PCs at the remote site need to reach this virtual server, and
    while most do, some have trouble seeing it.

    A common thread seems to be whether the 3560 has been able to learn
    the MAC address of the PC. If it hasn't, we can put in a static
    address and everything is OK.

    I'm wondering... is there a limit to the number of dynamic MAC
    addresses that a switch like the 3560 can learn? If so, can that limit
    be changed, and is the situation the same for static addresses?

    Also, is the limit of total MAC addresses for the switch fixed, or can
    that be changed?

    Thanks!
    pfisterfarm, Jan 26, 2010
    #1
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  2. pfisterfarm

    pfisterfarm Guest

    Just wanted to follow up with some more details on this network set
    up...

    [remote side 4500] ----> (CSME) ----> [central side 4500] ----> (ATM)
    ----> [central side 8540] ----> [vmware 3560] ----> [vmware server]

    the remote side has a vlan, let's call it 321, and the vmware server
    has a virtual machine set up for vlan 321. Most remote machines find
    the vmware server, and some find it one minute and not the next.

    The remote side has about 330 MAC addresses in the vlan in question.
    The central side 4500 never seems to learn more than about 200 or so.
    I'm assuming that the central side 4500 learns mac addresses from the
    remote side, and passes it through the 8540 (configured for IRB) to
    the 3560. None of the central side devices seem to learn much more
    than 200 of the MAC addresses and I'm not sure where that limitation
    would be. Does anyone have any idea what's going on here?
    pfisterfarm, Jan 26, 2010
    #2
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  3. pfisterfarm

    bod43 Guest

    On 26 Jan, 21:25, pfisterfarm <> wrote:
    > Just wanted to follow up with some more details on this network set
    > up...
    >
    > [remote side 4500] ----> (CSME) ----> [central side 4500] ----> (ATM)
    > ---->  [central side 8540] ----> [vmware 3560] ----> [vmware server]
    >
    > the remote side has a vlan, let's call it 321, and the vmware server
    > has a virtual machine set up for vlan 321. Most remote machines find
    > the vmware server, and some find it one minute and not the next.
    >
    > The remote side has about 330 MAC addresses in the vlan in question.
    > The central side 4500 never seems to learn more than about 200 or so.
    > I'm assuming that the central side 4500 learns mac addresses from the
    > remote side, and passes it through the 8540 (configured for IRB) to
    > the 3560. None of the central side devices seem to learn much more
    > than 200 of the MAC addresses and I'm not sure where that limitation
    > would be. Does anyone have any idea what's going on here?


    I don't recall a per VLAN limit but the MAC adddress
    table in switches is implemented in hardware and there is a
    total limit. It is certain to be way more than 330 though
    thousands and thousands.

    Ah! 8540!

    Maybe I should have mentioned when I indicated the IRB
    config earlier that the 8540 etc. was a somewhat problematical
    device. Wouldn't touch one with a barge pole.

    Remember that "missing" MAC addresses do not normally
    cause a lack of communications since frames to Unknown
    addresses are flooded out of all ports in the VLAN and so
    do reach the destination.

    I will have a closer look later and see of I can think how to
    investigate.

    Is this the Network with Unicast Flooding Prevention
    turned on? That simply limits all normal traffic to some level.
    Maybe that was another thread. Sorry, bit busy right now
    and cant check.
    If it is turn it off.
    bod43, Jan 26, 2010
    #3
  4. pfisterfarm

    pfisterfarm Guest

    This issue turned out to be a limit to learned MAC addresses on the
    CSME (AT&T) side. Increasing the limit made all problems go away...
    Thanks for your help!
    pfisterfarm, Jan 27, 2010
    #4
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