Missing entries in Mac Address Table?

Discussion in 'Cisco' started by Jason, Feb 26, 2008.

  1. Jason

    Jason Guest


    I'm studying for my CCNA exam, at some point I inadvertantly cleared all
    entries from the mac address table on my 2950 switch, including the CPU
    entries. I have recently been noticing some strange behaviour from this
    switch, for example with port security not quite working correctly & was
    wondering if the two could be related, I have since wiped the switch
    (including vlan.dat) but the mac address table is still missing the CPU
    entries. I only noticed these missing entries when I did a show mac-
    address-table on my other 2950 & saw the difference (see below). How can I
    get these entries back & hopefully return my switch to full functionality?
    All suggestions greatly received as I have my exam in April & am studying
    very hard at the moment.

    TIA, Jase

    SWITCH1#show mac-address-table
    Mac Address Table

    Vlan Mac Address Type Ports
    ---- ----------- ---- -----
    1 0004.274c.9ca0 DYNAMIC Fa0/1
    1 0040.63d8.ba0a STATIC Fa0/12
    1 0040.63d8.bab8 DYNAMIC Fa0/4
    10 0004.274c.9ca0 DYNAMIC Fa0/1
    Total Mac Addresses for this criterion: 4

    SWITCH2#show mac-address-table
    Mac Address Table

    Vlan Mac Address Type Ports
    ---- ----------- -------- -----
    All 000d.28f3.1680 STATIC CPU
    All 0100.0ccc.cccc STATIC CPU
    All 0100.0ccc.cccd STATIC CPU
    All 0100.0cdd.dddd STATIC CPU
    1 0004.274c.9ca0 DYNAMIC Fa0/1
    1 000a.f4cb.dcc2 DYNAMIC Fa0/1
    1 0040.63d8.ba0a STATIC Fa0/11
    1 0040.63d8.bab8 DYNAMIC Fa0/1
    2 000a.f4cb.dcc2 DYNAMIC Fa0/1
    3 000a.f4cb.dcc2 DYNAMIC Fa0/1
    10 000a.f4cb.dcc2 DYNAMIC Fa0/1
    Total Mac Addresses for this criterion: 11

    SWITCH1#show version
    Cisco Internetwork Operating System Software
    IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(11)EA1, RELEASE
    SOFTWARE (fc1)
    Copyright (c) 1986-2002 by cisco Systems, Inc.
    Compiled Wed 28-Aug-02 10:25 by antonino
    Image text-base: 0x80010000, data-base: 0x80528000

    ROM: Bootstrap program is CALHOUN boot loader

    SWITCH1 uptime is 1 hour, 6 minutes
    System returned to ROM by power-on
    System image file is "flash:/c2950-i6q4l2-mz.121-11.EA1.bin"

    cisco WS-C2950-12 (RC32300) processor (revision G0) with 20402K bytes of
    Processor board ID FOC0638Y10G
    Last reset from system-reset
    Running Standard Image
    12 FastEthernet/IEEE 802.3 interface(s)

    32K bytes of flash-simulated non-volatile configuration memory.
    Base ethernet MAC Address: 00:0A:F4:CB:DC:C0
    Motherboard assembly number: 73-5782-11
    Power supply part number: 34-0965-01
    Motherboard serial number: FOC06380C9A
    Power supply serial number: PHI06350618
    Model revision number: G0
    Motherboard revision number: A0
    Model number: WS-C2950-12
    System serial number: FOC0638Y10G
    Configuration register is 0xF
    Jason, Feb 26, 2008
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  2. Jason

    Jason Guest

    For anyone who is interested I have solved the mystery of the missing
    MAC address table entries & strange switch behavior. It seems that the
    switches were running different versions of IOS.

    SWITCH1 was running version:


    with SWITCH2 running version


    Once I copied the IOS from SWITCH2 to SWITCH1 everything started working
    correctly & the MAC address tables matched. I think the MAC address
    table in SWITCH1 was always missing the CPU entries but I only noticed
    when compared to SWITCH2, and I wrongly assumed that I had somehow
    deleted them - it's all part of the learning curve i suppose.

    Jason, Feb 27, 2008
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