Cogent IPv6

Chris Adams cmadams at hiwaay.net
Wed Jun 8 22:33:29 CDT 2011


Once upon a time, William Herrin <bill at 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).

-- 
Chris Adams <cmadams at hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.




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