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Addressing mode

Four levels of addressing mode are used in an internet employing the TCP/IP protocols: physical (link) addresses, logical (IP) addresses, port addresses, and specific addresses.

Relationship of layers and addresses in TCP/IP

1. Physical Addresses

• The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN.

• For example, Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC). LocalTalk (Apple), however, has a I-byte dynamic address that changes each time the station comes up.

Example:As we will see in Chapter 13, most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:

07:01:02:01 :2C:4B

A 6-byte (12 hexadecimal digits) physical address.

2. Logical Address

• Logical addresses are necessary for universal communications that are independent of underlying physical networks.

• A logical address in the Internet is currently a 32-bit address that can uniquely define a host connected to the Internet.

• No two publicly addressed and visible hosts on the Internet can have the same IP address.

The physical addresses will change from hop to hop, but the logical addresses usually remain the same.

3. Port Address

• In the TCPIIP architecture, the label assigned to a process is called a port address.

• A port address in TCPIIP is 16 bits in length.

4. Specific Address

• Some applications have user-friendly addresses that are designed for that specific address.

• Examples include the e-mail address (for example, [email protected]) and the Universal Resource Locator (URL) (for example, www.mhhe.com). The first defines the recipient of an e-mail the second is used to find a document on the World Wide Web.

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