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Community Member

Weird MAC behaviour

There are PC A and PC B. PC A has an IP address reserved in DHCP. PC A was switched on and after some work was done user switched it off. PC B is configured with a static IP address belonging to PC A (by accident). It is left switched on. When PC A is switched on, port security is activated and the port is shutdown. The port reported that the MAC address of PC B was found.

Does anyone knows what is going on?

Community Member

Re: Weird MAC behaviour

Sounds like you need to correct the duplicate IP address and then 'clear arp-cache'. Since PC B has the current entry in the arp cache when PC A comes on and shows the same IP address it matches it to the duplicate arp entry.

Community Member

Re: Weird MAC behaviour

I still do not understand.

Whose arp cache is corrupted? The switch does not have any arp entries on PC A and PC B. Port security is only activated when the illegal MAC is seen from the port. So how did the illegal MAC end up there?



Re: Weird MAC behaviour

Can't think of a logical reason for this as I don't see why port security would pay any attention to layer 3 addresses. Might be a bug in whatever IOS/CatOS version you're using.

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