On December 26, 2008, in Uncategorized, by

Gobbley gook right?

Maybe not..

Link-local IPv6 Address . . . . . : fe80::f8b0:4285:cb4e:9b0d%10

First hint on how to read that is to remember that repeating 0000’s can be simplified with “::”

So that IP address above is really….


Yeah okay still not much better.  Let’s break it down.

fe80:0000:0000: is the Network prefix

0000 is the subnet ID

4285:cb4e:9b0d%10 is the Interface identification

Or it’s supposed to be… but there’s a slight twist in our tale.

Those “link local” IPv6 addresses that you see are similar to the APIPA Addresses (the auto assigned if you don’t have an DHCP address) and they are only for local routing.

Identifying IPv6 Link Local Addresses:

Okay let’s look first at that network prefix: 

fe80:: means local network use
ff00:: means multicast traffic
2001:: for larget ISP inter-domain routing and
2002:: for IPv6 to IPv4 gateway networks

The subnet ID for most flat IPv6 networks will be 0000.

The last part, the interface identification is populated with MAC address. 

Physical Address. . . . . . . . . : 00-21-9B-57-3A-08

Now I know you are saying that that sure doesn’t look like that last part of the IPv6, but since the MAC address is a 48 bit value and the interface is 64bit, the MAC address is expanded to fill the space using the EUI format specified by the IEEE.  The expansion uses the first three octets of the MAC address, appends the constant value of ff:fe and the appends the last three bytes of the MAC address to form the interface.


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