Using /31 for router links

Tony Varriale tvarriale at
Sat Jan 23 17:24:49 UTC 2010

That's a vendor specific issue.  Maybe you could take it up with them and 
ask what year they think this is?

----- Original Message ----- 
From: "Florian Weimer" <fw at>
To: "Seth Mattinen" <sethm at>
Cc: "nanOG list" <nanog at>
Sent: Saturday, January 23, 2010 4:06 AM
Subject: Re: Using /31 for router links

>* Seth Mattinen:
>> 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?
> Bad.  For some systems, such tricks work to some degree only due to
> lack of input validation, and you get failures down the road (ARP
> ceases to work, packet filters are not applied properly and other
> fun).
> And now is not the time to conserve address space.  You really should
> do everything you can to justify additional allocations from your RIR.

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