IPv6 question

[John Blakley]

All,

I have a question about how IPv6 is in relation to IPv4. How can I tell, or is it even necessary, to what subnet an IPv6 address belongs to?

For example:

I know that 192.168.1.0 and 192.168.2.0 are different subnets.

I can't find in any documentation that I've read that this type of concept exists in IPv6. I've set up v6 on a couple of routers in GNS3, and I was able to ping across the link with no issues. I set up link-local addresses with autoconfigure (FE08::0001:0002:0003). I noticed that the only difference between the two routers were the ":001". It was on R1 as :001 and R2 was :002. Okay, I assume that's the subnet (because the numbers after I believed to be the host). I changed it to something totally off the wall like :CA04, and I was still able to ping from R2.

Does anyone have experience with v6 yet?

thanks,

John

[Giuseppe Larosa · Accepted solution]

Hello John,

ipv6 link local are addresses that conform to EUI-64.

the subnet is FE80:0000:0000:0000/64

what ever you see is in the host portion so it can be different I guess you have it on serial interfaces.

If you enable ipv6 on a LAN interface you see FE80::/64 + a modified version of the lan MAC address (indeed called EUI-64).

for this reason link local are not routable by definition: it is always the same subnet everywhere but it is very useful for a lot of tasks: neighbor discovery, routing protocols adjacencies and so on.

So you can still ping because you have only changed the host portion of the link local address.

see

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-addrg_bsc_con.html#wp1038809

Hope to help

Giuseppe

[John Blakley]

Giuseppe,

Thanks for the link!

John