Excellent explanation of a tricky concept Andrew. Jay
-----Original Message----- From: Trusz, Andrew [mailto:[EMAIL PROTECTED]] Sent: Tuesday, 24 September 2002 2:34 To: [EMAIL PROTECTED] Subject: [wdvltalk] RE: a bit OT - ip addresses 0.0.0.0 is all zeroes. 255.255.255.255 is all 1's. 127 = 01111111 128 = 10000000 191 = 10111111 192 = 11000000 223 = 11011111 224 = 11100000 The numbers you are looking at the arbitrary border lines between address classes: Class A= 1.0.0.0-126.0.0.0 127 reserved for loopback Class B= 128.0.0.0 - 191.255.0.0) Class C= 192.0.0.0 - 223.255.255.0 Class D= 224 multicast (D & E can be ignored) Class E= 240 reserved for future use Understanding the bit about all 1's or all 0's requires understanding the difference between network id and host id in an IP address. Generally clear as mud the first dozen times you look at it. The starting point is that the internet is a network of networks so there is a difference between what goes on between networks and what goes on within a network. An IP address consists of two parts: the IP and a subnet mask. You can't make sense out of an IP address without both parts. The subnet mask tells you which part of the IP is the network id and which part is the host id. Internet routers only care about the network id. The router sends the message to the network indicated by the subnet mask. Your network router and switches care about the host id so that a message can be sent to the machine it is intended for. In the simplest cases, the subnet mask would look like this: Class A addresses - 255.0.0.0 Class B addresses - 255.255.0.0 Class C addresses - 255.255.255.0 The non-zero numbers indicate which octets are part of the network id. So an address of 1.5.230.123 and a subnet mask of 255.0.0.0 would mean "send this packet to network 1.0.0.0". The router at network 1.0.0.0 would look for machine 5.230.123 and deliver the packet there. Within a network, two address are special: the all 0's and the all 1's. The all 0's identifies the network itself (1.0.0.0) in this example, with a binary of 00000001.00000000.00000000.00000000. No machine will have this address. This is your all 0's address. Routers/switches use it to find the network. The all 1's within a network is the broadcast or multicast address. It would be 00000001.11111111.1111111.1111111 in this example. Any message sent to that address, would be sent to all the machines on the network. The point being that it is the host id which is either 0's or 1's. You have to separate the parts to understand it. And of course it is not this simple since bits in the host id can be "given back" to the network id. But that's another story. Work at it for awhile, it does eventually become clear or it becomes internet "magic". andy -----Original Message----- From: Pablo Oliva [mailto:[EMAIL PROTECTED]] Sent: Monday, September 23, 2002 3:25 AM To: [EMAIL PROTECTED] Subject: [wdvltalk] a bit OT - ip addresses I read that the following network numbers are reserved, that are all 0's and 1's in binary: 0.x.x.x 127.x.x.x 128.0.x.x 191.255.x.x 192.0.0.x 223.255.255.x I know that the conversion of decimal 127 is 1111111 in binary, so that makes sense. But how does 128.0.x.x convert to all zeros or ones. 128 = 10000000 ??? Can someone enlighten me please. ____ * The WDVL Discussion List from WDVL.COM * ____ To Join wdvltalk, Send An Email To: mailto:[EMAIL PROTECTED] Send Your Posts To: [EMAIL PROTECTED] To change subscription settings to the wdvltalk digest version: http://wdvl.internet.com/WDVL/Forum/#sub ________________ http://www.wdvl.com _______________________ You are currently subscribed to wdvltalk as: [EMAIL PROTECTED] To unsubscribe send a blank email to %%email.unsub%% ____ * The WDVL Discussion List from WDVL.COM * ____ To Join wdvltalk, Send An Email To: mailto:[EMAIL PROTECTED] Send Your Posts To: [EMAIL PROTECTED] To change subscription settings to the wdvltalk digest version: http://wdvl.internet.com/WDVL/Forum/#sub ________________ http://www.wdvl.com _______________________ You are currently subscribed to wdvltalk as: [EMAIL PROTECTED] To unsubscribe send a blank email to %%email.unsub%% ____ � The WDVL Discussion List from WDVL.COM � ____ To Join wdvltalk, Send An Email To: mailto:[EMAIL PROTECTED] Send Your Posts To: [EMAIL PROTECTED] To change subscription settings to the wdvltalk digest version: http://wdvl.internet.com/WDVL/Forum/#sub ________________ http://www.wdvl.com _______________________ You are currently subscribed to wdvltalk as: [email protected] To unsubscribe send a blank email to [EMAIL PROTECTED]
