Using /31 for router links
nanog at daork.net
Fri Jan 22 22:11:12 CST 2010
On 23/01/2010, at 1:31 PM, Jay Nugent wrote:
> On Fri, 22 Jan 2010, Seth Mattinen wrote:
>> In the past I've always used /30's for PTP connection subnets out of old
>> habit (i.e. Ethernet that won't take unnumbered) but now I'm considering
>> switching to /31's in order to stretch my IPv4 space further. Has anyone
>> else does this? Good? Bad? Based on the bit of testing I've done this
>> shouldn't be a problem since it's only between routers.
> 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.
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