On Tuesday 28 May 2002 11:06 pm, Erik C Elmshauser wrote: > Hi, this is my first post to the list. > > I agree with Stephen, these netmasks are (as far as I can tell) > meaningless. Because of the way that you compute network addresses by > comparing a mask to an address the 255.255.0.128 mask just will not do > what you expect.
I would say that depends rather a lot on what it is you expect.... So long as you expect the right thing, these rather weird netmasks (sorry, Ramin, can't think of a better name for them) will work just the way they're supposed to. > For more info check out: > ftp://ftp.isi.edu/in-notes/rfc1878.txt No, that RFC deals only with netmasks following the standard convention of all the 1 bits on the left and all the 0 bits on the right. Here we're talking about masks where the 1s and 0s can be mixed up a whole lot more than that. They work just the same as 'normal' netmasks - you do a bitwise AND between the IP address and the mask, exclusive-OR with the network address, and if the answer's zero, the IP address belongs within the network range. If it's not, then it doesn't. None of this should be taken to imply that I'm aware of anyone having a good reason for actually using these strange things though :-) Antony.
