On Fri, 22 Feb 2002, Michael O'Donnell wrote: > Aren't there two IP broadcast addresses? > One consisting of all zeroes and the other all ones?
Not exactly. 255.255.255.255 is the "universal" broadcast address -- any host which receives a packet for that address is supposed to process it. Routers are not supposed to forward packets to that address. Take a network address, and set the "node" part to all ones (binary), and you have the broadcast address for that particular IP network. The network address with the "node" part set to all zeros (binary) is simply the network address. Some early IP implementations used that as the broadcast address, but that is not considered "correct". For example, take network 192.168.123.0/24. The first three bytes are the network part, and the last byte is the node part. Here are the important numbers: Net mask 255.255.255.0 11111111.11111111.11111111.00000000 Network 192.168.123.0 11000000.10101000.01111011.00000000 First node 192.168.123.1 11000000.10101000.01111011.00000001 Last node 192.168.123.254 11000000.10101000.01111011.11111110 Broadcast 192.168.123.255 11000000.10101000.01111011.11111111 There is also the "all subnets" broadcast address which meant something more interesting before CIDR/VLSM became common. I'm not sure it is even used anymore. It is/was a way to send a packet to all nodes within an entire subnet'ed network. For example, take class A network 10.0.0.0/8 and subnet it into a bunch of class C networks (10.0.0.0/24, 10.0.1.0/24 ... 10.255.254.0/24). You could, in theory, send to 10.255.255.255 and get every node in the entire class A network. The above is subject to being wrong. :-) -- Ben Scott <[EMAIL PROTECTED]> | The opinions expressed in this message are those of the author and do not | | necessarily represent the views or policy of any other person, entity or | | organization. All information is provided without warranty of any kind. | ***************************************************************** To unsubscribe from this list, send mail to [EMAIL PROTECTED] with the text 'unsubscribe gnhlug' in the message body. *****************************************************************
