IPv6 addressing for core network

Wed Feb 9 09:48:04 UTC 2011

> Is there a NANOG FAQ we can add this to?
> 
> > 1-  Use Public Ipv6 with /122 and do not advertise to Internet
> > 2-  Use Public Ipv6 with /127 and do not advertise to Internet
> 
> The all zeros address is the all routers anycast address so on most non-Cisco routers you can't use it, ruling out /127. The top 128 addresses in any subnet are also reserved anycast addresses although they don't do much in practice. So the longest prefix length you should use is /120 and only use addresses 1 - 127.

A /127 mask is still the best way to handle real point-to-point links
like SDH/SONET today, to avoid the ping-pong problem. Works fine with
Cisco and Juniper, not tried with other vendors.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no