Link local for P-t-P links? (Was: IPv6 prefixes longer then /64: are they possible in DOCSIS networks?)

Tom Lanyon tom+nanog at
Fri Dec 2 00:26:43 UTC 2011


On 01/12/2011, at 12:45 PM, Mike Jones wrote:
> Link-Local?
> [snip]
> Am I a complete idiot missing some obvious major issues with link
> locals, or am i just the only one not thinking IPv4-think? Opinions?
> :)

In a DC / hosting provider context, we're doing this.

We started out assigning all of our PtP links (where we had /31s in the IPv4 world) IPv6 /64s and addressing using ::1 and ::2 with /127 masks from these /64s (to address potential ND table overflow concerns), but have now settled on using automatic link-local addresses instead.

Our IGP propagates the routers' /128 loopbacks and these are used for routing user traffic.

Having the IGP table only contain the /128 loopbacks, and none of the PtP networks is nice. :)

On 01/12/2011, at 12:52 PM, Ray Soucy wrote:
> I for one get really irritated when my traceroutes and pings are
> broken and I need to troubleshoot things. ;-)  But I guess something
> has to give.

You don't have to give up working traceroute / ping to use link-local on your PtPs.  

Our traffic routes through globally reachable router loopbacks which looks pretty in traceroutes, are pingable and doesn't break PMTUD.


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