How to assign a MAC address to a WAN interface?

[carlosrpz26@gmail.com]

Hello first off I'm a newbie in this so please be patient with my question.

I've been working at the university with a Cisco Router of the 2500 series, it's the 2509. And when I see the details of the WAN interface it doesn't display a MAC address, just like the ethernet 0 or other interfaces. Why is that? I've been told that there is a way to assign a MAC address but I couldn't find anything about it, I've been searching at IEEE 802.3, and several more sites, but couldn't find anything about assigning MAC adresses to WAN interfaces or how to do it. Or if it even exists.

Thanks for your time and patience.

[Leo Laohoo]

Post the complete output to the command "sh interface <WAN interface> | i address is".

The MAC address of the interface is after the "address is" and before the "bia" or burnt-in-address.

[carlosrpz26@gmail.com]

I can't right now, since I'm at home, and router is at school, but I'm going to do it.
Thanks for your answer btw.

[Julio E. Moisa]

Hi

In order to see the MAC address of a interface you can execute this commando

show interface <interface id> ; example: show interface g0/0 

Your will see somthing like 

GigaEthernet0/0 is up, line protocol is up
Hardware is ABC, address is aabb.ccdd.1234 (bia aabb.ccdd.1234)

Now if you want to modify the MAC address, you can use:

interfae f0/0

mac-address abcd.1234.5678

* It is valid for physical interfaces only, not for subinterfaces or logical interfaces. 

Also you can use: Show ARP

Please don't forget to rate the comment if it was useful.

:-)

[Richard Burts]

The original post identifies the router as a 2509 (which is very old - but I am old enough to remember it clearly). But does not identify which interface is the WAN interface. My guess is that the WAN interface is a serial interface, and in that case there is no way to assign a MAC address on the interface.

HTH

Rick

[carlosrpz26@gmail.com]

Ok, I haven't uploaded the sh int log because the router is in my school, in México, due to the earthquake we can't access to the lab yet. So I just contacted my professor who is supposedly to send that info to me, but he has not done it yet.

Now, the interface is serial interface, and why there is no way to assign a MAC address on the interface? Professor (who sometimes lies to us so we can look up things seen in class and corroborate, which don't know if this is the case) said , there is a way, when you stablish communication the MAC is assigned, but as I said before, I'm a newbie and kind of doing this all by myself, full of doubts.

Thank you very much for your time.

P.S: I'm not looking for you to give a detailed explanation (I understand you got stuff to do), but if you know in which book or site I can look this up I would be really thankful.

[carlosrpz26@gmail.com]

Thank you very much for your answer, I hadn't been in the lab since the earthquake, but I'm going to test this.

P.S: Sorry for late answer

[Julio E. Moisa]

Hi

I have one 2509 and one 2511 used as access server please let me verify if it is possible on these routers. 

[carlosrpz26@gmail.com]

Guys, thanks for your replies, this is a capture of what is shown in the interface.

Why there isn't a MAC address in this interface?

[Richard Burts · Accepted solution]

Thank you for the additional information. This confirms that your WAN interface is a serial interface. Serial interfaces are very different from Ethernet interfaces and can use encapsulations such as PPP (used in this example) or HDLC. These serial encapsulations have their own method of local addressing which are different from Ethernet and these serial encapsulations do not use MAC addresses. So there is not any way to assign a MAC address on this serial interface.

HTH

Rick

[Julio E. Moisa]

Hi 

I agree with Richard, serial interface does not have MAC address like Ethernet has. Please check this link:

https://supportforums.cisco.com/t5/lan-switching-and-routing/mac-address-of-serial-interface/td-p/837656