bob mcgregor wrote:
>
> IP Subnet 0 is now possible if you have newer routers.  We use it here
> for about 8 class  C address and have had no problems what so ever.
> We subnet it between 1-126 and 129-254(usable ip's) and it works
> great.

You can also have variable length subnet masks (VLSM) which are
supported in networks running RIPv2, OSPF, and some other protocols.
Under this scheme you can have several "large" subnet blocks but still
reserve some other addresses for use as point-to-point nets.  Borrowing
some cisco output:

     Subnet                Hosts            Hosts            Broadcast
     Address               From             To               Address

192.168.0.0                192.168.0.1      192.168.0.254
192.168.0.255
     192.168.0.0           192.168.0.1      192.168.0.62
192.168.0.63
          192.168.0.0      192.168.0.1      192.168.0.14
192.168.0.15
          192.168.0.16     192.168.0.17     192.168.0.30
192.168.0.31
          192.168.0.32     192.168.0.33     192.168.0.46
192.168.0.47
          192.168.0.48     192.168.0.49     192.168.0.62
192.168.0.63
     192.168.0.64          192.168.0.65     192.168.0.126
192.168.0.127
          192.168.0.64     192.168.0.65     192.168.0.78
192.168.0.79
          192.168.0.80     192.168.0.81     192.168.0.94
192.168.0.95
          192.168.0.96     192.168.0.97     192.168.0.110
192.168.0.111
          192.168.0.112    192.168.0.113    192.168.0.126
192.168.0.127
[snip]
You can use the inner-most two 64-address blocks, use the center two of
the 16-address blocks of the zero-block of 64, and further split the
zero-block of 16 to get two 4-host (point-to-point) links.

Using router features like cisco's "ip subnet-zero" does indeed allow
you to use the zero block (in which case you can steal addresses from
the broadcast block).  Even if your routing protocol doesn't do VLSM,
you can still get away with this using static routes.

Jeff Kell <[log in to unmask]>