iX 6.5)

26 Chapter2

Internet Daemon

Overview of inetd

The Internet daemon, or inetd, is the master server that coordinates

the use of individual network services on your system. It listens for

connection requests from other nodes on the network who want access

to a service such as tftpd or bootpd. The Internet daemon checks if the

requesting node has permission to use the service, starts the

appropriate server if it does and, optionally, records information about

the connection request.

Stream Services

The Internet daemon starts servers for both stream services and

datagram services. For stream services, which use the TCP/IP

protocol, inetd listens for connection requests on stream sockets.

When it detects such a request, inetd determines which service the

socket corresponds to and invokes a server for it. The server then

handles incoming data, providing a reliable, full-duplex bytestream

service to the requesting node. Once inetd has invoked the server, it

returns to listening for other connection requests.

Datagram Services

For datagram services, which use the UDP/IP protocol, inetd listens

for requests on datagram sockets. You can think of a datagram as a

connection request and the message all in one package. Unlike the

TCP/IP protocol, UDP/IP does not provide any message

acknowledgment, ﬂow control or sequencing. It is the simplest possible

service with the advantage of low communications overhead. When

inetd detects an incoming datagram, it invokes a server for that

message. Once a datagram has been delivered, the socket becomes

available for another incoming datagram. That is, there is no

“connection,” simply the delivery and receipt of the datagram. For this

reason, datagram service is sometimes referred to as “connectionless”

communication.