Using /126 for IPv6 router links

Owen DeLong owen at
Mon Jan 25 06:40:20 UTC 2010

On Jan 24, 2010, at 4:29 PM, Nathan Ward wrote:

> On 24/01/2010, at 5:28 PM, Leo Bicknell wrote:
>> In a message written on Sat, Jan 23, 2010 at 01:52:21PM +0100, Mathias Seiler wrote:
>>> I use a /126 if possible but have also configured one /64 just for the link between two routers. This works great but when I think that I'm wasting 2^64 - 2 addresses here it feels plain wrong.
>>> So what do you think? Good? Bad? Ugly? /127 ? ;)
>> I have used /126's, /127's, and others, based on peers preference.
>> I personally have a fondness for /112's, as it gives you more than
>> 2 addresses, and a DNS bit boundary.
>> For all the pontification about how there are enough /64's to number
>> all the grains of sand, or other nonsense, I think that ignores too
>> much operational information.
>> rDNS is important, and becomes harder in IPv6.  Making it easier
>> is importnat.
>> Having a scan of a /64 fill your P2P T1 is poor design, all because
>> you assigned 2^64 addresses to a link that will never have more
>> than 2 functional devices.
>> Most importantly, we should not let any vendor code any of these
>> into software or silicon, in case we need to change later.
> I too prefer /112s. I can take the first /64 in any assignment or allocation and set it aside for networking infrastructure.
> The first /112 is for loopbacks, the remaining /112s are for linknets.
> Then I can filter this /64 at my border, and it's easy.
> You can do the same thing with /64 linknets, but then you have to set aside a block of them, and that might get hard if you have a /48 or something. Maybe not. What if you have a /56?
If you have link nets, you probably shouldn't have just a /48 and you CERTAINLY shouldn't have just a /56.


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