Cogent IPv6

Jack Bates jbates at
Thu Jun 9 15:43:00 UTC 2011

On 6/9/2011 10:02 AM, William Herrin wrote:
> I follow the reasoning, but unless you attach undue importance to the
> colons you get basically the same result with a /124.
> I guess choosing /112 for a point to point link is one of the weird
> side-effects of placing :'s in the address at fixed locations instead
> of arbitrary locations that serve the writer's mnemonic convenience.

For the most part, you are correct. I generally run a 
:town:router:linkid:linkaddresses format out of a single /64 per 
regional area. While I could shorten the number of linkaddresses more, 
I'm not sure of the need.

Even if I assigned it as a /124, I'd still allocate it as a /112 and 
just set the first 2 nibblets as 0. My reluctance to do so has more to 
do with uniformity, especially when providing support. It's much easier 
to rattle off the standard length than to have to look it up. There are 
cases where a /124 wouldn't be enough.

Honestly, it's all a matter of preference. There are technical issues 
against using /127 and there's pros and cons to using longer than /64. 
There are interoperability issues as well as ping pong handling issues. 
It was just my opinion that 16 bits was more than enough for each branch 
of allocation that I wanted.


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