do we support non contiguous netmasks ?

[Andre Oppermann]

Anders Lowinger wrote:
> 
> Andre Oppermann wrote:
> 
> >>   interface ethernet 0
> >>    ip address 192.168.0.0 mask 255.255.253.0
> >
> > This is simply a supernet (aka classless) but *not* a non-contignous
> > netmask.  A non-contignous netmask would look like 255.254.255.0.
> 
> Nope, 255.255.253.0 binary is 11111111.11111111.11111101.00000000
> which is non-contignous.

You are right.  I was looking to quickly.  However at least my Cisco
doesn't like it: "Bad mask 0xFFFFFD00 for address", IOS 12.2(10).

>  > With the your second example hosts on the network have
> > to have different default gateways (192.168.0.1 and 192.168.2.1)
> > depending in which network range they are.  In your first example
> > you just have one default gateway for all of them.  However the
> > netmask has to match on all hosts otherwise you run into all sorts
> > of wierd trouble.
> 
> In this case, the above is normally only used during a migration
> phase (as I mentioned, this is the only use of non-contignous i've
> seen, joining two separate subnets), so the hosts already have the
> correct default-route in their subnet. Hosts could optionally then
> be migrated to a common subnet.

Never heard of that (only supernets/subnets with respect to classful
notation), never done it and at least my Cisco 7500 doesn't like it.
So I doubt others have got their Cisco to like it.

-- 
Andre