Eben King wrote:
> The conversation at
> http://lists.netfilter.org/pipermail/netfilter/2001-October/027593.html
> says discontiguous netmasks are accepted by Linux tools, and violate
> only an IETF ruling.
>
>> here are the valid masks:
>>
>>
>> 255.255.255.255.0 11111111.11111111.11111111.00000000 254 hosts
>> 255.255.255.255.128 11111111.11111111.11111111.10000000 126 hosts
>> 255.255.255.255.192 11111111.11111111.11111111.11000000 62 hosts
>> 255.255.255.255.224 11111111.11111111.11111111.11100000 30 hosts
>> 255.255.255.255.240 11111111.11111111.11111111.11110000 14 hosts
>> 255.255.255.255.248 11111111.11111111.11111111.11111000 6 hosts
>> 255.255.255.255.252 11111111.11111111.11111111.11111100 2 hosts
>> 255.255.255.255.254 11111111.11111111.11111111.11111110 0 hosts
>
>
> Do the {low,high}est address actually _mean_ something special, or are
> they just typically used that way? What about using x.x.x.x/32 to refer
> to one host? Is that a pathological case and therefore requires a
> special case?
>
It's possible that some OSs can recognize discontiguous masks but if you
ran into a scenario that you needed one, then (I can't think of one)
then it is in best interest to redesign your network as to not
incorporate a ugly hack like that :)
Sure you can use /32 to represent one host. Sometimes a network engineer
will use a /32 mask for a loopback address of a router. There are
limited scenarios where you would want to use it but valid non the less.
I'm not sure what you mean buy this question "Do the {low,high}est
address actually _mean_ something special, or are
they just typically used that way?"
also I made a mistake with too many 255s lol!
255.255.255.0 11111111.11111111.11111111.00000000 254 hosts
255.255.255.128 11111111.11111111.11111111.10000000 126 hosts
255.255.255.192 11111111.11111111.11111111.11000000 62 hosts
255.255.255.224 11111111.11111111.11111111.11100000 30 hosts
255.255.255.240 11111111.11111111.11111111.11110000 14 hosts
255.255.255.248 11111111.11111111.11111111.11111000 6 hosts
255.255.255.252 11111111.11111111.11111111.11111100 2 hosts
255.255.255.254 11111111.11111111.11111111.11111110 0 hosts
remember the only purpose of the subnet mask is to define the
sub-network boundaries. They allow the TCP stack to know whether or not
to arp for a local IP address or arp for the router interface to send
data to a different network.
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