Re: IPv6 addressing for core network

[Sam Stickland <sam () spacething org>]

On 9 Feb 2011, at 09:48, sthaug () 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)