HP 200 Series Services And Applications page 133

Internet Protocol Routing Service
IP Filters
Packet Filters
In addition to routing protocol filters, HP routers also support packet filters
that can be used to secure the network or to control traffic flow. Packets can
be forwarded, dropped, or passed to subsequent filters based the contents of
specific fields within the IP packet, UDP packet, or TCP segment headers—
examined either singly or in combination. You can filter on the source or
destination IP address of the network or node. You can also filter on the
application that sent the packet, using the TCP/UDP source or destination
port on each network interface.
TCP/UDP port filters use well-known transport-layer port numbers for
higher-layer services such as Telnet, FTP, and TFTP. The User Datagram
Protocol (UDP) and Transmission Control Protocol (TCP) are internet trans-
port-level protocols. TCP provides a reliable connection mode packet serv-
ice while UDP provides connectionless datagram service. UDP packets and
TCP segments are originated by ports and addressed to ports. Ports are
logical abstractions used by transport-level protocols to distinguish between
multiple sources and destinations at a single host.
To facilitate application-to-application data flow, the Internet has assigned
well-known port numbers to certain commonly used application programs.
Examples of well-known port numbers include port numbers assigned to
remote-login (Telnet) programs, file-transfer programs, and remote-job-entry
(RJE) programs.
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