[c-nsp] IPv6 Subnetting - Service Provider

[Seth Mattinen]

Paul Stewart wrote:
> Hi there...
> 
> In a SP environment, what's common practice so far with subnetting?
> Typically, in IPv4 today we use a /30 or /29 for point to point and each
> device has a /32 loopback...
> 
> I've been reading a lot of different opinions and everyone seems to
> recommend a /64 for each link (router) or a server - why so large?  I'd love
> to see a layout of a few routers in a SP core network and how they've
> subnetted them....;)
> 

I just ran into an issue in my network (testing a 3750) where an IPv6
ACL only accepts down to a /64 for matching and only EUI-64 hosts. And
there's my 877W I've mentioned a few times this week that has its own
exciting quirks.

Other than that, I use /64 for subnets and /128 loopbacks out of a /64
reserved for loopbacks. Using /64 and /128 is almost guaranteed to be
safe at this early stage; plenty of IPv6 support just isn't that mature
yet. There's an RFC or something out there (too lazy to look it up) that
says use /64 for subnets, so it's the magic number for a lot of IPv6
implementations.

~Seth