NAME

ppp − Point-to-Point Protocol (PPP)

SYNOPSIS

ppp

DESCRIPTION

The Point-to-Point protocol (PPP) is a method for transmitting datagrams over point-to-point serial links.  This implementation of PPP is compliant with RFC1331, RFC1332, and the Internet Draft “The PPP Authentication Protocols” with the following exceptions: the 32-Bit FCS (Frame Check Sum) feature of RFC1331 is not implemented; Link Quality Control Protocol negotiation described in RFC1331 is not accepted; and the Challenge-Handshake Authentication Protocol defined in the Internet Draft is not implemented.  PPP is not IP specific like SLIP, but the current implementation only supports transmission of IP datagrams over serial links. 

The Point-to-Point protocol is implemented as a multiplexing STREAMS driver (PPPSM) that is linked beneath IP when internetworking is started.  The PPPSM manages the routing of IP datagrams between the interfaces presented to IP and the physical links to remote hosts (PPC).  It also performs PPP specific operations concerned with negotiating PPP operating parameters when PPCs are established and tearing down PPCs when they are no longer needed. 

The interfaces presented to IP are specified in /etc/inet/strcf and are created and marked up when slink(1M) is started.  The PPC links are NOT established to remote hosts until a pending datagram intended for a known remote host is detected by the PPPSM.  The interfaces presented to IP are marked as point-to-point interfaces and as such have a known destination IP address.  There may be a number of different physical links available that can be used to reach the destination host.  The PPC links are described in the PPP and UUCP configuration files. 

When a PPP data request (IP datagram) is detected, the PPSM will notify the Point-to-Point Connection Information Daemon (PPCID), in.pppd [see pppd(1M)] that a pending datagram exists for a specific destination IP address.  in.pppd will then check it’s configuration files for information on how to reach the remote host.  Using that information, in.pppd performs a uucp(1) style login to the remote host and negotiates the line characteristics at both the local and remote hosts.  Once the negotiation has finished and the PPC is established, the tty representing the link is linked beneath the PPPSM and the PPPSM is given information about the link.  The PPPSM now uses the link for its IP datagram traffic.  The PPC will continue to exist under the PPPSM until a pre-set count-down timer measuring continuous link inactivity has expired, or the link is broken by administrator command, i.e. using ifconfig(1M) to mark the interface down. 

During negotiation of a PPC, either side may require password authentication to ensure authorization for a PPP connection.  The daemon in.pppd verifies authorization by consulting the /etc/inet/pppauth file (see pppauth(4) . 

PPP provides a command, pppstat (see pppstat(1M)), for retrieving and displaying PPP interface statistics. 

SEE ALSO

ifconfig(1M), slink(1M), ppp(1M), pppd(1M), hosts(4), ppphosts(4), strcf(4), asyhdlc(7), pppauth(4), pppstat(1M),
RFC1331,
RFC1332,
Internet Draft “The PPP Authentication Protocols” by B. Lloyd and W. Simpson