Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 415 — #441

Linux in the Network

UDP User Datagram Protocol: A connectionless, insecure pro-

tocol. The data to transmit is sent in the form of packets

generated by the application. The order in which the

data arrives at the recipient is not guaranteed and data

loss is a possibility. UDP is suitable for record-oriented

applications. It features a smaller latency period than

TCP.

ICMP Internet Control Message Protocol: Essentially, this is

not a protocol for the end user, but a special control

protocol that issues error reports and can control the

behavior of machines participating in TCP/IP data

transfer. In addition, a special echo mode is provided by

ICMP that can be viewed using the program ping.

IGMP Internet Group Management Protocol: This protocol

controls the machine behavior when implementing IP

multicast. The following sections do not contain more

information regarding IP multicasting, because of space

limitations.

Almost all hardware protocols work on a packet-oriented basis. The data

to transmit is packaged in packets, as it cannot be sent all at once. This is

why TCP/IP only works with small data packets. The maximum size of

a TCP/IP packet is approximately 64 kilobytes. The packets are normally

quite a bit smaller, as the network software can be a limiting factor. The

maximum size of a data packet on an ethernet is about ﬁfteen hundred

bytes. The size of a TCP/IP packet is limited to this amount when the data

is sent over an ethernet. If more data is transferred, more data packets need

to be sent by the operating system.

21.1.1 Layer Model

IP (Internet protocol) is where the insecure data transfer takes place. TCP

(transmission control protocol), to a certain extent, is simply the upper

layer for the IP platform serving to guarantee secure data transfer. The

IP layer itself is, in turn, supported by the bottom layer, the hardware-

dependent protocol, such as ethernet. Professionals refer to this structure

as the layer model. See Figure 21.1 on the following page.

415SUSE LINUX Enterprise Server