IPv6 addressing for core network

Wed Feb 9 13:35:03 UTC 2011

On 9 Feb 2011, at 09:48, sthaug at nethelp.no wrote:

>> 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.
> 

Can you elaborate on this? What's the ping-pong problem? 

Sam (who's experience is pretty much mostly ethernet)