Little home http://xavierds.com Mon, 17 Oct 2011 15:38:23 +0000 en hourly 1 http://wordpress.org/?v=3.2.1 IPv6 and the modified EUI-64 http://xavierds.com/2011/10/ipv6_and_the_eui-64/ http://xavierds.com/2011/10/ipv6_and_the_eui-64/#comments Mon, 17 Oct 2011 15:37:36 +0000 xavierds http://xavierds.com/?p=49 Read more »

]]> In my studies to being prepared to obtain the CCNP, I’ve been surprised by the quantity of materials on internet who are mistaken on a little detail about the generation of the IPv6 address when they show how to build and EUI-64 address.

The last 64 bits of and IPv6 address could be formed as a modified EUI-64 in the link-local and global address.

So as the normal transformation of a MAC (48 bits) into a EUI-64 you add right into the middle, between the company and vendor id “FF:FE”. The oversight come just after, where they forget to explain than also the Local/Global bit (7º) should be marked as a 1. With this, it would be easier to know if it’s or not an auto-generated address.

You can find more information about it in http://tools.ietf.org/html/rfc5342 http://tools.ietf.org/html/rfc4291  and http://en.wikipedia.org/wiki/IPv6_address

After an ifconfig you should be able to see something like this on your computer

eth0      Link encap:Ethernet  HWaddr 00:19:bb:d1:f0:2d
          inet6 addr: fe80::219:bbff:fed1:f02d/64 Scope:Link

So now we are going to transform our MAC address into the last 64 bits as you could see above.

1. Adding fffe between the company and vendor id.

00:19:bb:d1:f0:2d  -> 00:19:bb:ff:fe:d1:f0:2d

2. Changing the Local/Global bit to one

00 in hexadecimal is 0000 0000 in binary and we need to change the seventh one.

0000 0010 -> 02

3. Converting the address into the IPv6 format

02:19:bb:ff:fe:d1:f0:2d -> 219:bbff:fed1:f02d

I hope it help you ;)

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