On Wed, Jun 8, 2011 at 9:58 PM, Kelly Setzer <Kelly.Setzer@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 ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004