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32-bit address, unique in the world, containing a network number and a host number
within that network. IP datagrams can travel great distances.
UDP (User Datagram Protocol) supplies messages among ports on different hosts. The
UDP protocol defines a set of virtual destinations called protocol ports. These ports are
further defined as either well-known port assignments or dynamically bound ports. The
well-known ports are numbered 1-255 and specific ports are assigned to certain widely
used TCP/IP applications (e.g., telnet uses port 23).
TCP (Transmission Control Protocol) supplies virtual connections, and two-way, reliable,
ordered streams of bytes, with flow control, between ports on different hosts. Data transfer
is made reliable with checksums, sequence numbers, acknowledgments, and retransmis-
sion.
ARP (Address Resolution Protocol) maps from IP addresses to Ethernet addresses.
ICMP (Internet Control Message Protocol) is used internally by the network protocols for
control and error messages.
RIP (Routing Information Protocol) is one of several protocols used by routers to ex-
change information about routes. It runs over UDP.
Applications are programs that want to talk to each other across the network. They do so
by calling TCP or UDP. The most widely used network applications are electronic mail,
remote login, file transfer, file sharing, and remote printing.
Appendix TCP - B: TCP/IP addressing
This appendix provides an overview of the various TCP/IP address types, their structure,
and their assignment in the context of different network configurations.
IP address
An IP address is a 32-bit number divided into two parts: a network number, and a host
number that identifies a specific device (computer, printer, etc.), within that network. The
network number is on the left and the host number is on the right. The boundary between
the network number and the host number can move. The network number can use one,
two, or three bytes (and correspondingly, the host number can use three, two, or one byte).
The position of the boundary is determined by the IP address class. There are three IP
address classes: Class A, Class B, and Class C. (Classes D and E exist, but are not currently
used.)