3750 MAC Address Table

I am labbing MAC flooding attacks on my 3750 and came across a seemingly weird issue. When the table is full and I can see unicast frames on ports they weren't intended for 'show mac address-table count' still shows space for 40 more addresses. Are there some "slots" reserved on 3750s? I thought they might be for static entries, but after adding a few statics it seems that is not the case. I tried the same thing on a 3550 and it shows no address space available.

I upgraded to the latest IOS (12.2(53)SE2) with the same results.

Switch#show mac address-table count

Mac Entries for Vlan 1:
---------------------------
Dynamic Address Count  : 5960
Static  Address Count  : 0
Total Mac Addresses    : 5960

Total Mac Address Space Available: 40

Any insight is appreciated.

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Comments

ConstantlyLearning

Same bug in the two IOS version's you've tried?

Did a bit of googling and saw a couple of "show mac address-table count" outputs from 3750's that were exhausted and showed "Total Mac Address Space Available: 0"

kalebksp

Yeah, the versions were pretty close together. I suppose I should find an older version and give it a try.

Thanks

kalebksp

Yep, I switched to an older IOS and total space available goes to zero.

dynamik

What were you using perform the flooding?

kalebksp

I was using macof.