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.

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March 31, 2008

Question Of The Day: 31 March, 2008

Topic: IPv6

FastEthernet0/0 is up, line protocol is up
  Hardware is AmdFE, address is cc00.17b4.0000 (bia cc00.17b4.0000)
  Internet address is 100.1.1.1/24

r1(config)#ipv6 unicast-routing
r1(config)#int fa0/0
r1(config-if)#ipv6 address 2001:B00B:1E5:1::/64 eui-64

What will r1’s fao/o IPv6 address be after this configuration is applied?

Click Here For Answer


Yesterday’s Question

 Question Of The Day: 28 March, 2008 

Topic: Route Summarization

You have the following subnets in your network:

132.16.32.0/24
132.16.121.0/24
132.16.34.0/24
132.16.33.0/24
132.16.5.0/24
132.16.181.0/24
132.16.27.0/24
132.16.2.0/24

Write a single summary route that will encompass all of these routes while being as specific as possible.

Answer: 132.16.0.0/16

Since the first two octets (132.16) are the same we need to look at the third octet.  Since we’re writing a single line we can just use the lowest (2) and highest (181) values:

132.16.2.0     10000100 00010000 00000010 00000000
132.16.181.0 10000100 00010000 10110101 00000000

I this case we can see that the first bits that are different the first bits of the 3rd octet.  We can stop right there.  Everything before those bits will be our network address (132.16.0.0) and the rest will be our mask (255.255.0.0)  Our summary will be 132.16.0.0/16.

Route Summarization

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