On Wed, Jun 8, 2011 at 9:58 PM, Kelly Setzer <kelly.set...@wnco.com> wrote: > IPv6 newbie alert! > > I thought the maximum prefix length for IPv6 was 64 bits, > so the comment about a v6 /112 for peering vexed me. I > have Googled so much that Larry Page called me and > asked me to stop. > > Can someone please point me to a resource that explains >how IPv6 subnets larger than 64 bits function and how >they would typically be used?
Hi Kelly, IPv6 netmasks work exactly like IPv4 netmasks. You can even route /128's if you want. Two major caveats: 1. SLAAC (stateless autoconfiguration, the more or less replacement for DHCP) only works if the subnet on your LAN is exactly /64. So unless you're manually configuring the IPv6 address on every machine on your subnet, you're using a /64. 2. Reverse DNS delegates every 4 bits (in IPv4 its every 8 bits). And when you write the address, every 4 bits is one digit. So unless you want to make things needlessly hard, you're also going to choose 4-bit boundaries for everything. I.e. a /56 or a /60 but never a /57. Now, as to why they'd choose a /112 (65k addresses) for the interface between customer and ISP, that's a complete mystery to me. Regards, Bill Herrin -- William D. Herrin ................ her...@dirtside.com b...@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004
