CCIE Pursuit Blog

August 17, 2008

Lab Tip: IPv6 EUI-64 Unexpected (For Me) Behavior

I ran across an unexpected behavior with IPv6 EUI-64 addressing today.  I had configured an interface with EUI-64 addressing.  Knowing that I would need to run OSPFv3 over this Frame Relay interface, I followed my normal procedure of creating a simplified link-local address.  To my surprise, this link-local address changed my EUI-64 address:

interface Serial0/0
 ipv6 address 2001:CC1E:1:1515::/64 eui-64
 ipv6 address FE80::1 link-local

r1(config-if)#do sh ipv int br | sec l0/0
Serial0/0                  [up/up]
    FE80::1
    2001:CC1E:1:1515::1

For some reason the EUI-64 part of the IPv6 address was replaced with the host address of the link-local address.

Let’s recreate the scenario by stripping off the IPv6 addressing:

r1(config-if)#int s0/0
r1(config-if)#no ipv6 address 2001:CC1E:1:1515::/64 eui-64
r1(config-if)#no ipv6 address FE80::1 link-local

r1(config-if)#do sh run int s0/0 | i l0/0|ipv
interface Serial0/0

r1(config-if)#do sh ipv int br | sec l0/0
Serial0/0                  [up/up]
    unassigned

Now configure the EUI-64 address:

r1(config-if)#int s0/0
r1(config-if)#ipv6 address 2001:CC1E:1:1515::/64 eui-64

r1(config-if)#do sh ipv int br | sec l0/0
Serial0/0                  [up/up]
    FE80::211:93FF:FEB0:7640
    2001:CC1E:1:1515:211:93FF:FEB0:7640

Now create add a link-local address:

r1(config-if)#int s0/0
r1(config-if)#ipv add FE80::1 link-local

r1(config-if)#do sh ipv int br | sec l0/0
Serial0/0                  [up/up]
    FE80::1
    2001:CC1E:1:1515::1

It’s good to know about this behavior in case you get a task that asks you to use an EUI-64 address.  Depending on the grading method, you could lose points for this.

Advertisements

1 Comment »

  1. I was able to duplicate the same behavior in my lab using dynamips. Have you found out why the global unicast address is changed when you modify the link-local address?

    Comment by Jimi — February 8, 2009 @ 3:01 am | Reply


RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Blog at WordPress.com.

%d bloggers like this: