First draft of the European Template for IP number requests

> > Looking at all possible subnet masks, you get:
> > 
> > subnet mask  |  # subnets | # hosts/subnet | total # hosts | usage
> > -------------+------------+----------------+---------------+------
> >     1:7      | not allowed|		       |	       |
> >     2:6      |     2      |      62        |     124       | 49 %
> >     3:5      |     6      |      30	       |     180       | 71 %
> >     4:4      |    14      |	     14	       |     196       | 77 %
> >     5:3      |    30      |	      6	       |     180       | 71 %
> >     6:2      |    62      |	      2	       |     124       | 49 %
> >     7:1      | not allowed|		       |	       |
> 
> Just one probably silly question - why should the subnet mask 1:7 not
> be allowed? If I get it right, you speak of netmask like 255.255.255.128.

Your interpretation is correct. The mask 1:7 (as 7:1) is not allowed
according to the recommendation to use all zeroes and all ones *neither* in
the host part, *nor* in the subnet part.

>From RFC1009 [Requirements for Internet gateways], page 6:

RFC1009> The bit positions containing this extended network number are
RFC1009> indicated by a 32-bit mask called the "subnet mask" [21]; it is
RFC1009> recommended but not required that the <Subnet-number> bits be
RFC1009> contiguous and fall between the <Network-number> and the
RFC1009> <Host-number> fields.  No subnet should be assigned the value
RFC1009> zero or -1 (all one bits).

> Which should let you have two subnets of 126 hosts each.

Similar reasons might have lead to the following

   B) In order to prevent implementation problems, network numbers ending
   with 0 or 255 should NOT be reassigned. 

found in ripe-72.txt . Just walking off the topic ...

  Peter