Point-to-Point Protocol daemon

Point-to-Point Protocol daemon (PPPD) is the <a href="/facts/Daemon_(computing)/bzuEVGGX">daemon</a> that implements <a href="/facts/Point-to-Point_Protocol/XLaU6D71">Point-to-Point Protocol</a> (PPP). PPP is used to manage network connections between two nodes on <a href="/facts/Unix-like_operating_system/YAKrAxzd">Unix-like operating systems</a>. It is configured using <a href="/facts/Command-line_argument/R9JpGmXQ">command-line arguments</a> and <a href="/facts/Configuration_file/DDzU0FLJ">configuration files</a>.
While it has initially been used to manage only <a href="/facts/Dial-up_Internet_access/gfhNU9s3">dial-up access</a>, it is also used to manage <a href="/facts/Broadband/nEn3A95N">broadband</a> connections such as <a href="/facts/Digital_subscriber_line/3pY5osov">DSL</a>, if <a href="/facts/Point-to-Point_Protocol_over_Ethernet/dSfSRACH">Point-to-Point Protocol over Ethernet</a> (PPPoE) or <a href="/facts/Point-to-Point_Protocol_over_ATM/IVy5A2RW">Point-to-Point Protocol over ATM</a> (PPPoA) is used.
The role of pppd is managing PPP session establishment and session termination. 
During session establishment, pppd has the role of:

<ul><li>Looped link detection: PPP detects looped links using <a href="/facts/Magic_number_(programming)/Xg7mVI7V">magic numbers</a>. 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.</li>
<li>Automatic self configuration: Using <a href="/facts/Link_Control_Protocol/WkSzWDjE">Link Control Protocol</a> it has to negotiate protocol features like Address-and-Control-Field-Compression (ACFC), escaped characters, and the compression, encryption (like <a href="/facts/Microsoft_Point-to-Point_Encryption/9GwwDoPx">MPPE</a>) and authentication methods to use.</li>
<li>Access control and authentication: Using protocols like <a href="/facts/Challenge-handshake_authentication_protocol/N80U6AFs">Challenge-handshake authentication protocol</a> (CHAP) or <a href="/facts/Password_authentication_protocol/YzWIg2yr">Password authentication protocol</a> (PAP) it has to provide and check authentication data.</li>
<li>Layer 3 configuration: If using <a href="/facts/Internet_Protocol_Control_Protocol/VzeMjjKK">Internet Protocol Control Protocol</a> (IPCP), it will negotiate or determine <a href="/facts/Internet_Protocol/Qq6VeEal">IP</a> parameters such as the <a href="/facts/IP_address/z9V22Sw9">IP addresses</a>, the <a href="/facts/Maximum_transmission_unit/l2FdKoLa">maximum transmission unit</a>, and <a href="/facts/Name_server/pUgmBMNW">name server</a> addresses. Some versions may also support Internetwork Packet Exchange Control Protocol (IPXCP) and AppleTalk Control Protocol (ATCP) for routing <a href="/facts/Internetwork_Packet_Exchange/TEGGak0E">IPX</a> or <a href="/facts/AppleTalk/6j3NRgTl">AppleTalk</a> over the link.</li>
<li>After negotiation is complete, it has to set up the required network interfaces and routes, so that the connection is run by the <a href="/facts/Kernel_(operating_system)/uEj4U3Rz">kernel</a>.</li></ul>
pppd terminates a PPP link when:

<ul><li>too many frames with invalid <a href="/facts/Frame_check_sequence/ywJNMuHd">frame check sequence</a> (FCS) field have been received</li>
<li>the link is considered "idle" (if configured)</li>
<li>another program or the peer requests link termination.</li></ul>
Some newer versions of pppd are also capable of handling <a href="/facts/Dial-on-demand_routing/TqbHn7g9">Dial-on-demand routing</a>, where pppd sets up a virtual network, captures the packages it receives and establishes a PPP connection and forwards the captured and not-yet transmitted packages over the link.

Point-to-Point Protocol daemon open-in-new

Point-to-Point Protocol daemon