Static Routing 172.16.0.0/32

Sun Dec 10 19:16:21 UTC 2017

On Fri, 8 Dec 2017, Ryan Hamel wrote:

> Greetings,
>
> A colleague of mine has static routed 172.16.0.0/32 to a usable IP address, to have a single known IP address be static routed to a regions closest server. While I understand the IP address does work (pings and what not), I don't feel this should be the proper IP address used, but something more feasible like a usable IP in a dedicated range (172.31.0.0/24 for example).
>
> I would to hear everyone's thoughts on this, as this the first IP 
> address in an RFC1918 range.

Last time I tried using the first address of a classful address block 
(which 172.16.0.0/32 would be) in Cisco IOS (classic), that didn't work 
properly. This was in IOS 12.0.x. You can't set up BGP peers to something 
in the network address in classful network space, for instance. So 
172.16.0.0/32 or 172.16.255.255/32 wouldn't work (because it's first and 
last address of class B space), but 172.16.1.0 worked just fine (because 
in class B space, 172.16.1.0 isn't special).

So while this has been allowed per standardssince mid 90:ties, it's not 
obvious that it'll work in all operating systems that might still be in 
use.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se