On Sat, Jan 23, 2010 at 4:52 AM, Mathias Seiler <mathias.seiler@mironet.ch> wrote:
Hi In reference to the discussion about /31 for router links, I d'like to know what is your experience with IPv6 in this regard.
I use a /126 if possible but have also configured one /64 just for the link between two routers. This works great but when I think that I'm wasting 2^64 - 2 addresses here it feels plain wrong.
So what do you think? Good? Bad? Ugly? /127 ? ;)
Cheers
Mathias Seiler MiroNet GmbH, Strassburgerallee 86, CH-4055 Basel T +41 61 201 30 90, F +41 61 201 30 99 mathias.seiler@mironet.ch www.mironet.ch
As I mentioned in my lightning talk at the last NANOG, we reserved a /64 for each PtP link, but configured it as the first /126 out of the /64. That gives us the most flexibility for expanding to the full /64 later if necessary, but prevents us from being victim of the classic v6 neighbor discovery attack that you're prone to if you configure the entire /64 on the link. All someone out on the 'net needs to do is scan up through your address space on the link as quickly as possible, sending single packets at all the non-existent addresses on the link, and watch as your router CPU starts to churn keeping track of all the neighbor discovery messages, state table updates, and incomplete age-outs. With the link configured as a /126, there's a very small limit to the number of neighbor discovery messages, and the amount of state table that needs to be maintained and updated for each PtP link. It seemed like a reasonable approach for us--but there's more than one way to skin this particular cat. Hope this helps! Matt