PPP links

Each connection from the local host to a remote host over a serial line linked to the IP driver through the PPP STREAMS stack is a ``PPP link''. Each PPP link requires a unique network interface between the IP driver and the PPP driver called a PPP network interface. What makes each PPP network interface unique is the unique IP address assigned to the local host for this link and the unique IP address assigned to the remote host for this link.

A network application on the local host uses a PPP link by specifying an IP address that is the remote host IP address of an existing PPP network interface. For example:

telnet 132.147.118.7

The application can also specify a host name if the local host can translate that host name to an IP address.

When the IP driver receives a packet whose destination IP address is associated with a PPP network interface, as in the example above, the IP driver routes the packet to the PPP driver via the network interface. In turn, the PPP driver puts the packet out on the serial line associated with that PPP network interface. When the PPP driver receives a packet over the serial line, it passes it to the IP driver via the unique network interface associated with the link over which the packet came.

Before a networking application can use PPP:

• root must install the PPP stack and create one or more endpoint configurations that are used to set up PPP links. See ``PPP endpoint configurations'' for detailed information on endpoint configurations.

• the PPP daemon must be started and it must read the endpoint configurations. Typically, a line in the /etc/tcp script starts the PPP daemon if the PPP configuration file /etc/ppphosts exists. The PPP daemon reads the endpoint configurations each time it starts up or when sent a SIGHUP signal. See ``Signaling the PPP daemon'' for information on signaling the daemon.

Multiple applications (or multiple instances of the same application) on a local host can communicate with the same remote host using the same PPP link. Use of the same PPP link requires only that the applications use the same IP address to specify the remote host. By using different IP addresses to specify the same remote host, two applications can also use individual PPP links to the same host, provided a separate serial line is available for each separate address and both addresses have unique PPP network interfaces.

Once a PPP link is established, it remains active until the administrator marks the interface down or the idle timer expires. You can use ifconfig to mark an interface down. The idle timer is set in the PPP endpoint configuration.

The following sections discuss PPP concepts in detail:

• ``SCO PPP features''

• ``PPP negotiation''

• ``PPP configuration files''

• ``How UUCP is configured for outgoing dialup''

• ``Signaling the PPP daemon''

• ``Logging PPP information''

• ``PPP packet filtering''

• ``PPP authentication methods''

• ``PPP gateway''

• ``Proxy ARP''

• ``Complex PPP connection scenarios''

• ``PPP MIB support''

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