nanog mailing list archives
Re: Cogent IPv6
From: Chuck Anderson <cra () WPI EDU>
Date: Thu, 9 Jun 2011 08:01:47 -0400
On Wed, Jun 08, 2011 at 10:33:29PM -0500, Chris Adams wrote:
Once upon a time, William Herrin <bill () herrin us> said: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.I had to ask this here a while back, so I can now share. :-) IPv6 addresses are written as 8 16-bit chunk separated by colons (optionally with the longest consecutive set of :0 sections replaced with ::). A /112 means the prefix is 7 of the 8 chunks, which means you can use ::1 and ::2 for every connection. Of course, just because you allocate a /112 (or shorter) in your database doesn't mean you have to use it. You could also allocate a /112 for a point-to-point link and use a /127 (e.g. addresses ::a and ::b).
Please don't use /127: Use of /127 Prefix Length Between Routers Considered Harmful http://tools.ietf.org/html/rfc3627 More below on use of various prefix lengths. You need to watch out for the EUI-64 'u' and 'g' bits, as well as subnet anycast addresses (top 127 addresses of every subnet): IPv6 Addressing Considerations: http://tools.ietf.org/html/rfc5375 IPv6 Address Assignment to End Sites: http://tools.ietf.org/html/rfc6177 Emerging Service Provider Scenarios for IPv6 Deployment: http://tools.ietf.org/html/rfc6036 IPv6 Optimal Address Plan and Allocation Tool: http://www.ipv6book.ca/allocation.html ARIN Wiki: http://www.getipv6.info/index.php/IPv6_Addressing_Plans (but some of the ARIN-related concepts here are obsolete, such as references to the HD Ratio and non-nibble-boundary allocations)
Current thread:
- Re: Cogent IPv6, (continued)
- Re: Cogent IPv6 Owen DeLong (Jun 08)
- RE: Cogent IPv6 Kelly Setzer (Jun 08)
- Re: Cogent IPv6 William Herrin (Jun 08)
- Re: Cogent IPv6 Chris Adams (Jun 08)
- Re: Cogent IPv6 Aftab Siddiqui (Jun 08)
- Re: Cogent IPv6 Jack Bates (Jun 09)
- Re: Cogent IPv6 William Herrin (Jun 09)
- Re: Cogent IPv6 Jack Bates (Jun 09)
- Re: Cogent IPv6 Joel Jaeggli (Jun 09)
- RE: Cogent IPv6 George Bonser (Jun 09)
- Re: Cogent IPv6 Chuck Anderson (Jun 09)
- Re: Cogent IPv6 Rob Evans (Jun 09)
- Re: Cogent IPv6 Grzegorz Janoszka (Jun 09)
- Re: Cogent IPv6 sthaug (Jun 09)
- Re: Cogent IPv6 Owen DeLong (Jun 09)
- Re: Cogent IPv6 Chuck Anderson (Jun 09)
- Re: Cogent IPv6 sthaug (Jun 09)
- Re: Cogent IPv6 Iljitsch van Beijnum (Jun 09)
- Re: Cogent IPv6 Ray Soucy (Jun 09)
- Re: Cogent IPv6 Nick Hilliard (Jun 09)
- Re: Cogent IPv6 Ray Soucy (Jun 09)