TCP/IP Basics IPv4 a 32 bit addressing scheme (note IPv6 for future use will not be covered) Class A: Enterprise 0-126 (except 10.X.X.X reserved) B: Medium 128-192.167 (except 172.X.X.X reserved) C: Small 192.169-223 (192.168.X.X reserved) Reserved addresses for intranet use. This allows for a userspace addressing scheme that will not cause address resolution trouble. xxx.xxx.xxx.xxx Range 0-255 (256 total numbers) the first octet determines the Class of the network. So an IP address of 22.222.47.1 would be a Class A network. This addressing scheme is good for computers not for humans so we use networ names to help us out. Using servers we convert an internet address to an IP address. So http://www.slashdot.org/ is sent to a DNS (Domain Name Server) and is translated to an IP address (66.35.250.150). In addition to the IP address we have ports they indicate a given service (usually). For instance port 80 is used for HTTP. Port numbers have to be in the range of 0-65535 (a 16 bit ID). Port Usage 21 = FTP 23 = telnet, SSH 24 = telnet, SSH 25 = SMTP 69 = TFTP 67 = bootpd 3000 = ntop 10000 = webmin The port numbers are divided into three ranges: the Well Known Ports, the Registered Ports, and the Dynamic and/or Private Ports. The Well Known Ports are those from 0 through 1023. The Registered Ports are those from 1024 through 49151 The Dynamic and/or Private Ports are those from 49152 through 65535 A good introduction to how the OSI 7 Layer Model works. Taken from http://www.pe.net/~rlewis/Resources/james.html [ed. - new URL as of Dec. 2004 is: http://www.lewistech.com/rlewis/Resources/james.aspx] " James Bond Meets The 7 Layer OSI Model James Bond meets Number One on the 7th floor of the spy headquarters building. Number One gives Bond a secret message that must get through to the US Embassy across town. Bond proceeds to the 6th floor where the message is translated into an intermediary language, encrypted and miniaturized. Bond takes the elevator to the 5th floor where Security checks the message to be sure it is all there and puts some checkpoints in the message so his counterpart at the US end can be sure he?s got the whole message. On the 4th floor the message is analyzed to see if it can be combined with some other small messages that need to go to the US end. Also if the message was very large it might be broken into several small packages so other spies can take it and have it reassembled on the other end. The 3rd floor personnel check the address on the message and determine who the addressee is and advising Bond of the fastest route to the Embassy. On the 2nd floor the message is put into a special courier pouch(packet). It contains the message, the sender and destination ID. It also warns the recipient if other pieces are still coming. Bond proceeds to the 1st floor where Q has prepared the Aston Martin for the trip to the Embassy. Bond departs for the US Embassy with the secret packet in hand. On the other end the process is reversed. Bond proceeds from floor to floor where the message is decoded. The US Ambassador is very grateful the message got through safely. "Bond, please tell Number One I?ll be glad to meet him for dinner tonight". "