[121696] in North American Network Operators' Group
Re: Using /126 for IPv6 router links
daemon@ATHENA.MIT.EDU (Owen DeLong)
Mon Jan 25 01:46:05 2010
From: Owen DeLong <owen@delong.com>
In-Reply-To: <D901B7DD-BE45-4AE7-B42A-697C020F2189@daork.net>
Date: Sun, 24 Jan 2010 22:40:20 -0800
To: Nathan Ward <nanog@daork.net>
Cc: nanOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jan 24, 2010, at 4:29 PM, Nathan Ward wrote:
>=20
> On 24/01/2010, at 5:28 PM, Leo Bicknell wrote:
>=20
>> 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.
>>>=20
>>> So what do you think? Good? Bad? Ugly? /127 ? ;)
>>=20
>> I have used /126's, /127's, and others, based on peers preference.
>>=20
>> I personally have a fondness for /112's, as it gives you more than
>> 2 addresses, and a DNS bit boundary.
>>=20
>> 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.
>>=20
>> rDNS is important, and becomes harder in IPv6. Making it easier
>> is importnat.
>>=20
>> 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.
>>=20
>> Most importantly, we should not let any vendor code any of these
>> into software or silicon, in case we need to change later.
>=20
> 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.
>=20
> Then I can filter this /64 at my border, and it's easy.
>=20
> 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?
>=20
If you have link nets, you probably shouldn't have just a /48 and you =
CERTAINLY shouldn't have just a /56.
Owen
