Using /31 for router links

Jay Nugent jjn at
Sat Jan 23 00:31:30 UTC 2010


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.

      --- Jay Nugent
          Nugent Telecommunications

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