Missing entries in Mac Address Table?


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 memory. 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

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Jason wrote in news:Xns9A50CC2421934SpamSpamSpamSpanishI@

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.


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