|
Tech Review #2 |
The IP Address IP: Internet Protocal
Pronounced as two separate letters, IP stands for Internet Protocol. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combine IP with the higher-level protocol called TCP, Transport Control Protocol, which establishes a virtual connection between a destination and a source. This combination is otherwise known as TCP/IP.
IP addresses are 32 bits in length. They are typically written as a sequence of four numbers, representing the decimal value of each of the address bytes. Since the values are separated by periods, the notation is referred to as dotted decimal. A sample IP address is 208.162.106.17.
Routing requirements demand that IP addresses be hierarchical. IP addresses are made up of into two subfields: 1) The Network Identifier (NET_ID) and the Host Identified (HOST_ID). The Net_ID identifies the TCP/IP subnetwork connected to the Internet and it is used for high-level routing between networks, much the same way as the country code, city code, or area code is used in the telephone network. The Host_ID indicates the specific host within a subnetwork.
Different address classes have been established to accomodate different sized networks. There are four major classes: A,B,C, and D. Classes A, B, and C are used for host addressing. Class D is used for multicast addresses.
Class A:
7-bit NET_ID and 24-bit HOST_ID.
The first digit of a Class A addresses will be a number between 1 and 126. Relatively few Class A addresses have been assigned; examples include 9.0.0.0 (IBM) and 35.0.0.0 (Merit).Class B
The first digit of a Class B address will be a number between 128 and 191. The Class B address space has long been threatened with being used up and it is has been very difficult to get a new Class B address for some time. Class B address assignment examples include 128.138.0.0 (WestNet) and 152.163.0.0 (America Online).Class C
The first digit of a Class C address will be a number between 192 and 223. Most addresses assigned to networks today are Class C (or sub-Class C!); examples include 208.162.102.0 (Hill Associates) and 192.80.64.0 (St. Michael's College, Colchester, VT).ClassD
The first digit of a Class D will begin with a value between 224 and 239. These are used for IP multicasting (i.e., sending a single datagram to multiple hosts); the IANA maintains a list of Internet Multicast Addrsses.
Hyperlinks for Further Research:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/55160.htm
Provides overview on IP from Cisco.
http://www.3com.com/nsc/501302.html
Understanding IP Addressing: Everything You Ever Wanted To Know from the 3Com Web Site
http://www.hill.com/library/tcpip.html
Good overview of Internet protocols, including sections on IP, ARP, OSPF, RIP, ICMP, and IPv6. Also includes links to all the RFCs that define the Internet protocols.
http://skip.incog.com/
Contains an overview of Simple Key management for Internet Protocols (SKIP) with links to news articles, source code and binaries, technical papers, and specifications
Page last updated on 05/30/2000.