As a matter of fact, an IPv6 address has a maximum (but not restricted) fixed lenght of 64 bits for the network and subnetwork definition, and 64bit for the interface identifier. The most left 64 bit in that address contains information about type of address, scope, network and subnetwork and another "useful" information. But the fixed restricted lenght is not mandatory, and if locally managed IPv6 addresses anre created, you can design routes via routing protocols to follow the same rules as in CIDR. Best regards xD. ------------------------------

Message: 2 Date: Wed, 8 Jun 2011 20:58:18 -0500 From: Kelly Setzer <Kelly.Setzer@wnco.com> Subject: RE: Cogent IPv6 To: "nanog@nanog.org" <nanog@nanog.org> Message-ID: < FC8ABE0E5D384A489CDB16C4A8EB77839B3E9C6995@MSMAIL01.LUV.AD.SWACORP.COM>

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-----Original Message----- From: ryan@u13.net [mailto:ryan@u13.net] Sent: Wednesday, June 08, 2011 9:19 AM To: nanog@nanog.org Subject: Re: Cogent IPv6

On Wed, 8 Jun 2011 09:51:21 -0400, Nick Olsen wrote:

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I'm sure someone here is doing IPv6 peering with cogent. We've got a Gig [SNIP] We have separate v4 and v6 sessions with them on the same dual-stack interface (a v4 /29 and v6 /112 on the interface). One session is between our v4 address and theirs, and carries v4 prefixes only. Then another session between v6 addresses that carries v6 prefixes only.

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?

thanks, Kelly

-- *Daniel Espejel Perez *