06-18-2021 09:52 AM
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
06-18-2021 10:14 AM
show ip arp ?
06-18-2021 10:22 AM
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.
06-18-2021 10:29 AM
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
06-18-2021 10:47 AM
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 ?
06-21-2021 03:12 AM
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?
06-21-2021 03:51 AM
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
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