The netmask would be 255.255.254.0 in this case; if you had four class
"C" addresses, the netmask would be 255.255.252.0. Note that to combine
two "C"s together, the low one needs to be even (so the example you gave
would NOT work) and to bind four class "C"s together, the lowest subnet
number would have to be a multiple of four. And, of course, they have
to be contiguous.
Also note that not all IP stacks support supernetting. For example,
you'd have to download Novell's latest TCPIP.NLM off their web site in
order to do this.
For more info, check out my TCP/IP Primer at
-- +|Daryl S. Banttari, CNE|mailto:firstname.lastname@example.org|http://www.2ndlevel.net/daryl|"Talk does not cook rice" - Chinese proverb|'Good things come to those who wait, but only the things left by | those who hustle.' - Abe Lincoln|'A candle loses nothing by lighting another candle' - Fr. James Keller|'There is a diminishing return on caution' - Me+