Using /31 for router links

Chris Costa ccosta at
Sat Jan 23 01:00:22 UTC 2010

We recently did a backbone router upgrade and the vendor surprisingly  
didn't support /31's.  We had to renumber all those interconnects and  
peering sessions to /30's.  That wasn't fun!

On Jan 22, 2010, at 4:53 PM, Seth Mattinen wrote:

> Joe Provo wrote:
>> On Fri, Jan 22, 2010 at 04:08:28PM -0800, 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.
>> rfc3021 is over 9 years old, so should be no suprise that it works  
>> well.  :-)
> I'm never surprised anymore by something that should work turning  
> out to have some obscure quirk about it, so I figured it was worth  
> asking. ;)
> ~Seth

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