Using /31 for router links

Florian Weimer fw at
Sat Jan 23 10:06:34 UTC 2010

* 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

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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