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According to Cisco's documentation:

"The MAC address tables on all stack members are synchronized. At any given time, each stack member has the same copy of the address tables for each VLAN."

However, when logged into the switch I see the following:

ny-swstack01#show mac ad | inc Total
Total Mac Addresses for this criterion: 222
ny-swstack01#ses 2

ny-swstack01-2#show mac ad | inc Total
Total Mac Addresses for this criterion: 229
ny-swstack01-2#exit

ny-swstack01#ses 3

ny-swstack01-3#show mac ad | inc Total
Total Mac Addresses for this criterion: 229
ny-swstack01-3#exit

ny-swstack01#ses 4

ny-swstack01-4#show mac ad | inc Total
Total Mac Addresses for this criterion: 235
ny-swstack01-4#exit

ny-swstack01#show mac ad | inc Total
Total Mac Addresses for this criterion: 222

Going back and forth this isn't just because it is changing over time either, within certain sessions there are entries that I don't seen from the master session:

ny-swstack01#show mac ad | inc Gi3/0/6
ny-swstack01#sess 3

ny-swstack01-3#show mac ad | inc Gi3/0/6
  72    001b.2193.17f0    DYNAMIC     Gi3/0/6

We are currently waiting to hear back on Cisco from this, but has anyone run into this before? I stumbled upon this when looking into Unicast flooding, in the above example, packets with a hard destination of 001b.2193.17f0 are part of the unicast flooding.

Also, I checked an all sessions show the same aging time.

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The command in question is showing -all- addresses in the cam table - not just dynamically learned entries. This is going to include locally generated addresses. Can you run through the same sequence again looking just at dynamically learned entries (i.e. show mac-address-table dynamic) or, if available, the total count (show mac-address-table count)? –  rnxrx Sep 25 '12 at 1:01
    
@rnxrx: The dynamic count is also different depending on the session it is run from. I also updated my question to show a specific example of a dynamic entry that shows up inside session 3, but not in the "master" session –  Kyle Brandt Sep 25 '12 at 12:33
    
Are the CAM timers set to default values? –  rnxrx Sep 25 '12 at 21:01
    
This is an interesting problem Kyle, out of curiosity, have to tried posting it over at supportforums.cisco.com/index.jspa ? –  jwbensley Nov 3 '12 at 17:34
    
Which model Cisco's? –  LapTop006 May 14 '13 at 7:37
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1 Answer

My guess would be that each stack member only has the MAC addresses it needs. For that vl72 example, on what stack members is vl72 present on? I'd be real interested in a diff showing which ones are missing (or added) in other locations.

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