[121611] in North American Network Operators' Group
Re: Using /31 for router links
daemon@ATHENA.MIT.EDU (Nathan Ward)
Fri Jan 22 23:11:51 2010
From: Nathan Ward <nanog@daork.net>
In-Reply-To: <Pine.LNX.4.44.1001221928110.8718-100000@home.nuge.com>
Date: Sat, 23 Jan 2010 17:11:12 +1300
To: nanOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 23/01/2010, at 1:31 PM, Jay Nugent wrote:
> Greetings,
>=20
> On Fri, 22 Jan 2010, Seth Mattinen wrote:
>=20
>> In the past I've always used /30's for PTP connection subnets out of =
old=20
>> habit (i.e. Ethernet that won't take unnumbered) but now I'm =
considering=20
>> switching to /31's in order to stretch my IPv4 space further. Has =
anyone=20
>> else does this? Good? Bad? Based on the bit of testing I've done this=20=
>> shouldn't be a problem since it's only between routers.
>=20
> Yes, this *IS* done *ALL* the time. P-t-P means that there are ONLY
> two devices on the wire - hence point to point. It ONLY uses two IP
> addresses (one on each end) and there is no reason or need to ARP on =
this
> wire. So no need for a broadcast or network addresses - it is just =
the
> two end points.
ARP is still required on ethernet links, so that the MAC address can be =
discovered for use in the ethernet frame header. /31 does not change the =
behavior of ARP at all.
--
Nathan Ward
