The only advantage of a 126-bit prefix is if you're using it to take advantage of the short address, and keep all your point-to-point networks in the same address space so that you can easily identify them. This is really only personal preference for network engineers who may not want to be dependent on DNS and like to have key link addresses committed to memory (we're only human, after all). Example: Prefix: 2001:DB8::/32 2001:DB8::4/126 (or 2001:DB8::5 and 2001:DB8::6) 2001:DB8::8/126 2001:DB8::B/126 etc. Though, you could accomplish almost the same thing with using a 64-bit prefix length: 2001:DB8:1::/64 (or 2001:DB8:1::1 and 2001:DB8:1::2 2001:DB8:2::/64 2001:DB8:3::/64 That said. By not using the 64-bit boundary you may be sacrificing performance optimizations with today's processors that lack operations for values larger than 64-bits. Either way is acceptable and is simply a matter of personal preference. Link networks do not contain a dynamic number of hosts, so logically there is no reason to accommodate more addresses than they originally call for. RFC 3627 recommends against using a 127-bit prefix-length due to potential (implementation specific) problems with DAD, and that is enough reason to avoid it for most people. Nobody is right. Nobody is wrong. It's just preference. We have a lot of link networks and opted early on to make use of 126-bit prefixes for them because that worked nicely for our allocation schema. On Mon, Jan 24, 2011 at 7:48 AM, Lasse Jarlskov <laja@telenor.dk> wrote:
Hi all.
While reading up on IPv6, I've seen numerous places that subnets are now all /64.
I have even read that subnets defined as /127 are considered harmful.
However while implementing IPv6 in our network, I've encountered several of our peering partners using /127 or /126 for point-to-point links.
What is the Best Current Practice for this - if there is any?
Would you recommend me to use /64, /126 or /127?
What are the pros and cons?
--
Best regards,
Lasse Jarlskov
Systems architect - IP
Telenor DK
-- Ray Soucy Epic Communications Specialist Phone: +1 (207) 561-3526 Networkmaine, a Unit of the University of Maine System http://www.networkmaine.net/