..Cisco switch not showing mac address for some devices

[cyberpete]

I have a Cisco switch environment and from time to time do a "sh cam dyn" to find mac addresses of devices associated with a particular port. I then run a "Sh ip arp aa.bb.cc" on the default gateway to the switch to get the ip address. From that I can get a netbios name - and from that - a user name (via our internal name convention procedure). HOWEVER now and then I find a switch port that shows is connected ok - no errors - but I cannot get a mac address - (hence I cant get the IP either). Surely all ethernet compliant devices will have a MAC address ? If so then why would the mac address tables on switches sometimes have no entry for it ? I can't quite see how an IP enabled device is going to work without a MAC address to be honest. Yours puzzled, dazed and slightly bemused.

Peter@it-123.co.uk

[amit-singh]

Hi Pete,

I have found out in some of my testings that If a PC doesnot genareate any kind of traffic and is totally ideal and once the MAC-address table ages out, it doesnot show its MAC untill the PC generates some kind of traffic.I guess this is what you must be seeing.

I have oberved one more thing that If I connect a fully booted PC which not generating any traffic to a switch port it doesnot learn its Mac-address untill its generates the traffic. This is what my obeservations is and that what I believe in most of the cases.

i dont know whether that answer your question or not but it could be something closer. I think there will be some who can put some more ligth on this.

regards,

-amit singh