IPs , Netmasks and Broadcast.

Jerry McAllister jerrymc at clunix.cl.msu.edu
Wed Sep 14 09:18:23 PDT 2005

> Hi All,
> Now I am really confused.
> Up until this morning I thought I had a good handle on when I need to use 
> the real Netmask and Broadcast.
> For example, If I have 3 servers, and my upline asigns me a block of 128 
> addresses, for the first ip used (from this block) on each server, I would 
> need to specify the IP, true netmask and a broadcase. Then, when using more 
> IPs from that block, I would use a netmask and a broadcast 
> equal to the IP.
> Today, I was in this exact position where I was tring to add an (the first 
> one one THAT machine, from that block) IP from a block that is almost 
> completely used up on another server, and the one I was adding it to would 
> not take it. When I tried adding it with a netmask, and a 
> broadcast eaqual to the amount of IPs from that block - it worked.

I am not sure I follow you correctly, but the way I understand it, on 
any given server, you would use the "real" netmask for only the first/main 
IP address.  All the rest of the aliases get the full 255 set.   It doesn't 
matter which block of IPs it is from.

> this is on a FreeBSD 4.10 machine.
> WHich way is correct for 4.7 and higher?
> -Grant
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