[135393] in North American Network Operators' Group
Re: IPv6: numbering of point-to-point-links
daemon@ATHENA.MIT.EDU (Crist Clark)
Mon Jan 24 19:23:11 2011
Date: Mon, 24 Jan 2011 16:22:58 -0800
From: "Crist Clark" <Crist.Clark@globalstar.com>
To: <bmanning@vacation.karoshi.com>
In-Reply-To: <20110124131820.GA10465@vacation.karoshi.com.>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
>>> On 1/24/2011 at 5:18 AM, <bmanning@vacation.karoshi.com> wrote:
> On Mon, Jan 24, 2011 at 02:10:48PM +0100, Marco Hogewoning wrote:
>> > While reading up on IPv6, I've seen numerous places that subnets are =
now
>> > all /64.
>> >=20
>> > I have even read that subnets defined as /127 are considered harmful.
>>=20
>> RFC3627, with a lot of discussion in the IETF on this. See also=20
> https://datatracker.ietf.org/doc/draft-ietf-6man-prefixlen-p2p/=20
>>=20
>> > However while implementing IPv6 in our network, I've encountered =
several
>> > of our peering partners using /127 or /126 for point-to-point links.
>>=20
>> I personally don't any benefit in using /126 subnets.
>>=20
>> > What is the Best Current Practice for this - if there is any?
>> >=20
>> > Would you recommend me to use /64, /126 or /127?=20
>> >=20
>> > What are the pros and cons?
>>=20
>> >From an operational point of view there is a risk that be using /64 =
somebody=20
> can eat away a lot of memory by either scanning or even changing =
addresses.=20
> This is also described in the draft above...
>>=20
>> I would personally recommend to at least always assign the /64, even if =
you=20
> would decide to configure the /127. RFC 3627 has been around long enough =
that=20
> you will keep running into equipment or software that won't like the =
/127. In=20
> which case you can always revert back to /64.
>> This will also allow you to use easy to remember addresses like ::1 and =
::2,=20
> saving you the headache of a lot of binary counting.
>>=20
>> Grtx,
>>=20
>> Marco
>=20
> this results in -very- sparse matrix allocation - which is fine, as long =
as you=20
> believe that=20
> you'll never run out/make mistakes. personally, i've use /126 for the =
past=20
> 12 years w/o any
> problems.
>=20
> there was never supposed to be a hard split at /64 - it was done as a =
means=20
> to simplify autoconfig.
All of the (mostly religious) arguments about /64 versus any
smaller subnets aside, I'm curious about why one would choose
/126 over /127 for P-to-P links? Is this some kind of IPv4-think
where the all-zeros and all-ones addresses are not usable
unicast addresses? This isn't true in IPv6 (of course, it's not
strictly true in IPv4 either). Is there another reason?
--=20
Crist Clark
Network Security Specialist, Information Systems
Globalstar
408 933 4387
