MAC address on L3 interface C1921

[AnzeZ]

Hi.
I am desperate here and I can't find solution, is there a way to check MAC address of connected device on L3 physical interface on Cisco router (1921)?

Kind regards

[balaji.bandi]

show ip arp ?

[Joseph W. Doherty]

Of course, what Balaji suggests would require the router to have "heard" an ARP reply.

If this hasn't happen, device will not be in router's ARP cache.

Sometimes, a ping to the subnet broadcast IP will get hosts to respond.  If that doesn't work, you can try individually pinging all the subnet's host IPs.

[AnzeZ]

This is not the case for me. I have router connected to a switch with Vlan X, this Vlan X goes through a network to a router that has IP address and is GW for my router. I would like to check MAC address of device connected to my router, in my case this is a switch. And of course, switch won't be in ARP in this case.

KR

[balaji.bandi]

In  your case (you know the device IP ?)

On router do you show ip arp, since Layer 3 in Router.,

On router show mac address-table show you the device connected to port - also show cdp neigh give you information about switch

show cdp neighbors gigabitEthernet x/x detail  - should able tio give you more information.

If you looking  end device here is proceedure.

show ip arp

example 192.168.1.10 have mac address x.x.x.x

take that mac address  and login to Layer 2 Switch

issue as below :

show mac address | in x.x.x.x  (the result will give you what port it connected)

is this make sense ?

[AnzeZ]

It all does make sense. In my case we are having some very specific problems and this might not be fully usefull for me, but:

As far as I understand, there is no command such as "show mac address-table", to show mac address of L2 switch connected to router on L3 interface?

[Giuseppe Larosa]

Hello @AnzeZ ,

if the switch is acting as a L2 switch you just need to look for the ARP of the desired gateway the switch acts as a transparent switch it does not change  the frames it moves from port to port so knowing the MAC address of the directly attached port is of little interest for a router or a host.

if your device was a L2 switch you could see the MAC address from STP

Hope to help

Giuseppe