In message <AANLkTinDQdH5Z==mbyvm-osta2m-wvkxo7vkylc8x...@mail.gmail.com>, Per Carlson writes: > Hi Owen. > > > The downside is that it doesn't provide enough bits for certain kinds of = > auto-topology > > management that are being considered by CE vendors. I highly recommend /4= > 8 instead. > > I've seen this claim (you need a /48) from your side several times, > but never seen any explanation why a /56 won't work. > > Is there any requirement that sub-delegations must happen on 8-bit > boundaries? AFAICS there is at least nothing in the RFC. Wouldn't for > example a nibble boundary work equally well (splitting a /56 into 16 > /60s, each containing 16 /64s)? > > I don't challenge the claim, I'm just trying to understand the > rationale behind it.
There is a model where the down stream CPE devices always request powers of two prefixes. It doesn't take many CPE devices daisy chained to exhaust 8 bits. The other model is to just request as many /64 as needed using multiple requests with different identifiers. You can daisy chain out past the limits of IPv6 to route packets with that model. Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org