How to FIND mac address from ip address.

mzinz

I had a question on my CCNA which asked how to find the MAC addresses of certain devices located on a network.

show arp?
show interfaces?
show protocols?

There were about 6 options. I chose show arp and show interfaces.. I had no idea.

This is not asking to issue the ARP command. Its asking the user to visually find the MAC addresses.

blackzone

I dont' know but, since you are taking CCNA, dont' you have access to a router or a simulator which you can check?

mzinz

I can't remember all of the choices, and I can't find a command that lists the MAC.

show arp does.. But I can't find another cmd that does.

blackzone

my guess the only way to find is pinging or connect to the device first, than use the show arp.

show interface shows only your router's mac address. It won't show the remote mac address.

Below is from my router.

Router#ping 10.10.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.0.1, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 1/2/4 ms
Router#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.0.1 0 0013.d4f5.5f0f ARPA Ethernet0
Internet 10.10.0.10 - 00e0.1e68.47c4 ARPA Ethernet0

Danman32

I got stumped on that one too the first time. I too was going for ARP then realizing on my way home that would not give me what I need to know. Then it hit me!

How about 'show mac-address-table'?

blackzone

I'm not too sure but does old router(2500,2600) have mac-address-table?

I thought it's mainly for cisco switch which I don't have.

Quick google search says better cisco router have it.

p.s. I don't really know. Over a year since I actually touched a cisco router.

hectorjhrdz

mmmmmmmm Does routers hava a mac-address-table?

it's for switches!!!

in deed i try to perform the "sh mac-address.table" table right now on a 6500 sw with routing module, in the routing module, and it doesn't recognize it.

!30

does routers hava a mac-address-table?

comon man , router's pass beyond L2 , so certainly they'll have a MAC address table , I assume it's right

rakem

its show arp.

check out this ouput:

Password:
ROUTER>en
Password:
Password:
ROUTER#sh arp ?
| Output modifiers
<cr>
ROUTER#sh arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.21.13 0 0002.a5ec.c7f9 ARPA FastEthernet0
Internet 10.1.21.10 0 0012.3fec.fb0d ARPA FastEthernet0
Internet 10.1.21.9 2 0014.220e.dac5 ARPA FastEthernet0
Internet 10.1.21.4 0 00c0.9f4b.8b76 ARPA FastEthernet0

and there is no show mac-address-table on routers, at least not on my one, unless its a layer 3 switch...

ROUTER#sh ma ?
% Unrecognized command
ROUTER#sh mac ?
% Unrecognized command
ROUTER#sh mac?
% Unrecognized command
ROUTER#sh m?
memory modem

mzinz

Thanks for the feedback.

'sh arp' was one of the commands I chose for my answer.

--Unfortunately, the answer was asking for TWO commands which could trace a Mac address. They were ALL 'show' commands (and mac-address-table wasn't one of them, and we now know why.)

Hopefully I don't get that question again!

rakem

actually, using the sh interfaces command does show you the mac addres,
check it out:

PNBEV con0 is now available
Press RETURN to get started.
User Access Verification

Password:
PNBEV>en
Password:
PNBEV#sh int
FastEthernet0 is up, line protocol is up
Hardware is PQUICC_FEC, address is 000d.285a.c57f (bia 000d.285a.c57f)
Description: P & N Beverages Ethernet
Internet address is 1.1.1.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
.........


So the answer would of been show arp and show interface

Danman32

OK, the first post said DEVICES. My stumped question was on a switch.

Show interfaces should provide the macs of the interfaces if I am not mistaken. You might need the keyword 'detail' though.

I didn't think show arp would show the local interface mac addresses.

bmauro

I didn't read all the responses so I apologize if this has already been said - but at work whenever I have a mac-address all I have to type on the router is:

Router#show ip arp 0025.7023.76c8

and the response should look something like:

Router#show ip arp xxxx.xxxx.xxxx
Protocol Address Age (min) Hardware Addr Type Interface
Internet xx.xx.xx.xx 131 xxxx.xxxx.xxxx ARPA GigabitEthernet0/0.111

bmauro

Oppss - sorry I did misread the post - BUT what I posted is still correct with a little modification

Router#show ip arp xxx.xxx.xxx.xxx //<-- IP address

that will still output

Protocol Address Age (min) Hardware Addr Type Interface
Internet xx.xx.xx.xx 131 xxxx.xxxx.xxxx ARPA GigabitEthernet0/0.111