Point-to-Point Protocol daemon

• Looped link detection: PPP detects looped links using magic numbers. When PPPD sends PPP LCP messages, these messages include a magic number. If a line is looped, the node receives an LCP message with its own magic number, instead of getting a message with the peer's magic number.
• Automatic self configuration: Using Link Control Protocol it has to negotiate protocol features like Address-and-Control-Field-Compression, escaped characters, and the compression, encryption and authentication methods to use.
• Access control and authentication: Using protocols like Challenge-handshake authentication protocol or Password authentication protocol it has to provide and check authentication data.
• Layer 3 configuration: If using Internet Protocol Control Protocol, it will negotiate or determine IP parameters such as the IP addresses, the maximum transmission unit, and name server addresses. Some versions may also support Internetwork Packet Exchange Control Protocol and AppleTalk Control Protocol for routing IPX or Appletalk over the link.
• After negotiation is complete, it has to set up the required network interfaces and routes, so that the connection is run by the kernel.

• too many frames with invalid frame check sequence field have been received
• the link is considered "idle"
• another program or the peer requests link termination.

Frontends and configurators

• kppp – A kde GUI frontend for pppd.
• gnome-ppp – A gnome GUI frontend for pppd.
• pppconfig – It uses the standard ppp configuration files and sets ppp up so that the standard pon and poff commands and plog can be used to control ppp. It includes modem detection.
• wvdial – A CLI tool which is used for modem initialisation before starting pppd.