The serial interfaces don't have mac address so even if you configure it to have one, the router won't use it to make the IPv6 link local address. The router uses another method that should allow both links to still come up with unique link local address. Are you using GNS3 or real equipment?
Regardless, I suggest you just manually configure the link local address for the interfaces.
As Beau said serial interfaces doesn't have MAC addresses, so how configure itself the link-local address? They do it by taking into account the MAC address of the Ethernet interface. That would no cause any problems until i know, since as it's name state it's a link-local address, so would be LOCAL for that link. I recommend you to see this post. https://learningnetwork.cisco.com/message/202659#202659
Post any doubt,
Thanks to all of you for your replies.
Ive been through the link Elvin sent but i am still confused here.
Why would the serial interface 'inherit' from other interfaces.
is it a good practice then (based on what i read ) to use
ipv6 address fe80::1111 link-local on serial links??
Plz somebody explain that to me...
Just some more cosigning here...
But, like we said, serial interfaces don't have mac addresses so they must get a mac address from somewhere! You would think that if you manually configure a mac address on the interface it would use that but it WON"T. Cisco documentation says it will use the first mac address in the routers pool of mac addresses. It seems that the first mac address in that pool is the lowest numbered ethernet interface (As Elvin said!)
I think it is good practice to manually configure the link local address. Scott mentioned on another post that he would configure all link local addresses on a single device to be the same (since they are link local and won't conflict). For instance, it could be beneficial if you are trouble shooting a link to R5 and you know without checking that the link local is always FE80::5555 because you configured your network in that way.
Yeah... And I had to stare at your last post for a minute because I was trying to figure out how you got from 5555 to FE9, FEA and FEB. But then the Mt. Dew kicked in... heheheheh.
But yes, and another thing people do a lot is to imbed the IPv4 management address of a device in the link-local. That way it is not only obvious, but also means something to you!
While FE80::1 makes perfect sense in a lab for R1, that doesn't really scale well in the real world!