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Community Member

IP answers to ping, but no MAC on switch port

Hello All,

I have a 6509 switch doing L3 and another 6509 connected via a trunk. I can ping an address and when I do a "sho IP arp", I see the mac. When I go to the other switch(where I know the device is connected) and do a "sho mac-address address" with the address, it comes back with nothing. Even when I do the "sho mac-addr...interface", there is no mac listed.

Any help would be appreciated.

Thanks,

Brian

5 REPLIES
Cisco Employee

Re: IP answers to ping, but no MAC on switch port

Hi Brian,

Do you see anything is the logs that the interface is going up and down which may cause the mac entry to loose from the cam table, just a guess.

Can you see that mac entry in "sh mac-address-table dynamic"

Regards,

Ankur

Community Member

Re: IP answers to ping, but no MAC on switch port

Ankur,

I thought that was the problem, but the switchport is stable. I also tried the "sho mac-addr....dyn" and searched thru every mac on the switch. Not there.

Brian

Community Member

Re: IP answers to ping, but no MAC on switch port

did you ever get this resolved?

I'm having the same issue with a 6513 and also some 3750s.

Re: IP answers to ping, but no MAC on switch port

Check the stability of spanning tree. a TCN sets the CAM age timer to 15 secs, which is pretty sharp! it is quite easy to take longer than that to check tables.

If the aging timer is set to 15 secs, the first thing is to make sure user ports are set to portfast to suppress TCNs for those ports when users turn a PC on, off, reload etc.

Community Member

Re: IP answers to ping, but no MAC on switch port

Hi Brian,

If the switch port down even device connected to the port it wont show the mac-address untill the switch port is up.

Regards,

Naidu.

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