[121684] in North American Network Operators' Group
Re: Using /126 for IPv6 router links
daemon@ATHENA.MIT.EDU (Nathan Ward)
Sun Jan 24 19:29:58 2010
From: Nathan Ward <nanog@daork.net>
In-Reply-To: <20100124042821.GA25165@ussenterprise.ufp.org>
Date: Mon, 25 Jan 2010 13:29:21 +1300
To: nanOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
>>=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.
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?
Maybe there is some value in linknets being effectively disposable so =
you never have to worry about problems coming from re-use. A single /64 =
full of /112s gives you 281 trillion.
For links to customers and other networks, I like /64s, because they are =
right now the standard so you're not going to run in to compatibility =
problems. If you've got links to customers you should have a /32, so =
setting aside a /48 or a /44 or something for those customer links is no =
huge drama.
--
Nathan Ward=
