[nsp] using /31s

[Mike Sawicki]

On Mon, Feb 09, 2004 at 02:30:14PM -0500, Jeff wrote:
> > I'm missing a nugget of clue -
> > 
> > edge2(config)#interface Serial6/0/4:0
> > edge2(config-if)#ip address 216.23.183.248 255.255.255.254
> > Bad mask /31 for address 216.23.183.248
> > edge2(config-if)#ip address 216.23.183.249 255.255.255.254
> > Bad mask /31 for address 216.23.183.249
> > edge2(config-if)#ip address 216.23.183.250 255.255.255.254
> > Bad mask /31 for address 216.23.183.250
> > edge2(config-if)#ip address 216.23.183.251 255.255.255.254
> > Bad mask /31 for address 216.23.183.251
> > 
> > 216.23.183.0/24 is VSLM'd but has mostly /30s.  I have essentially two /30s
> > left (216.23.183.248/30, 216.23.183.252/30) and figured I'd double that with
> > /31s but I'm having issues with IOS accepting it.
> 
> I am not sure if you are being serious here, but a /31 is an invalid
> netmask.
> 
> It will only give you the network and broadcast, no actually usable IP
> Addresses.

Jeff is right.  The only time I ever use /31's is to reference ip pairs 
in filtering/acl applications.  This is really the only realm in
which they are valid.  Try 'ip unnumbered' if you are getting
desperate for space.

Mike Sawicki
fifi at HAX.ORG