Force some packets to activate a port and find the MAC-address

[pierrek7]

On my switches (2960 family) I see active ports (green light) but since the host didn't talk to the LAN for a while I cannot find its MAC-address, and I don't have the IP either. Is there a command in Cisco IOS that forces some packets to talk to the interface so it "activates" the host, then I could "sh mac-a int f0/4" ?

[Edison Ortiz]

Try pinging the broadcast address for that subnet or you can run a ping sweep with any network management utility.

[cadet alain]

Hi edison,

the broadcast ping won't work for some OS like windows XP, I haven't tried with Vista and Seven but I presume

that as it was a security concern it hasn't changed since then.

Regards.

Alain.

[milan.kulik]

Hi,

as Edison said "...or try to Ping sweep."

Tools like this http://www.eusing.com/ipscan/free_ip_scanner.htm

are able to Ping each host in a large subnet very fast (just disable scanning ports and chose "Only scan IP addresses" in the Options).

You just need to know the IP range your host should be using.

But as it's your LAN, you should know it.

HTH,

Milan

[cadet alain]

Hi Milan,

as Edison said "...or try to Ping sweep."

I agree with both of you but just wanted to mention  that first method would not work for Windows hosts.

Regards.

Alain.

[hobbe]

Well that all depends on.

If it is/has a firewall then it might not answer your packets at all.

However most systems responds to arp.

so how do we get them to respond ?

"pinging" would result in an arp.

shut and no shut the ports in the switch.

That would in most cases create either a gratitious arp or a dhcp request.

but I agree it might not be the most gracefull way to get the mac address.

Good luck

HTH