TCP/IPv6 Configuration and Management Manual (G06.24+)

NonStop TCP/IPv6 Protocols and Configuration Files
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-008
D-3
Internet Protocol (IP)
As for TCP, (described in Transmission Control Protocol (TCP) on page D-2),
application processes call a socket routine to request the NonStop TCP/IPv6 software
to create a UDP socket when needed; the application specifies the type of service
desired. The TCP and UDP protocols assume that the Internet Protocol (IP) is used for
network layer services. Like IP, UDP is a connectionless protocol; it uses datagrams.
TCP, however, is a connection-oriented protocol, requiring a connection to be
established before messages are sent.
TCP messages specify the connection with which they are associated. For UDP, the
same combination of addresses and numbers described for TCP identifies a temporary
source and destination, rather than a connection. This combination is a part of every
UDP packet that goes over the Internet.
For a detailed description of the socket library routines available, refer to the TCP/IP
Programming Manual. For more information on the UDP, refer to RFC 768 (DDN
Protocol Handbook, Volume 2, DDN Network Information Center, December, 1985, pp.
2-175 through 2-178). Also, refer to the book TCP/IP Illustrated by W. Richard Stevens,
Prentice Hall, 1994.
Internet Protocol (IP)
The Internet Protocol (IP) accommodates the connectionless delivery of Internet
datagrams between heterogeneous networks. The IP also services various host-to-
host protocols. The IP provides many capabilities at the network level, and forms the
foundation of the NonStop TCP/IPv6 product. The TCP and UDP protocols use the IP
protocol. Applications can build their own transport-layer protocols directly on this
protocol by using raw sockets.
Message Routing
In the IP, messages called datagrams pass from a source (host) to a destination. An IP
datagram can consist of one or several network-layer messages, or packets.
Datagrams in the Internet often pass through a dozen different networks before
reaching their final destination. The message routing is performed by the IP and is
transparent to the application. The application only needs to specify its own local
Internet address and the remote Internet address of the destination.
The IP uses routes, which are Internet paths, to transmit datagrams. A route specifies
both a final destination and the gateway or host to which a datagram must be sent next
to reach that destination. The IP layer at each host maintains a table of routes. The
table lists the Internet address of each accessible network, or of a particular accessible
host on a network, and the gateway used to get to that network or host.
To keep their routing tables simple, hosts often specify a default gateway or router to
which datagrams can be sent if the routing table contains no entry for a particular
network. The hosts thus rely on the gateways, which contain comprehensive routing
tables, to determine the best path for the datagram.