1.1. Overview

Mpd is a netgraph(4) based implementation of the multi-link PPP protocol for FreeBSD. It is designed to be both fast and flexible as it handles configuration and negotiation in user land, while routing all data packets strictly in the kernel.

Mpd has unified support for many link types:

• modem to connect using different asynchronous serial connections, including modems, ISDN terminal adapters, and null-modem. Mpd includes event-driven scripting language for modem identification, setup, manual server login, etc.
• pptp to connect over the Internet using the Point-to-Point Tunneling Protocol (PPTP). This protocol is supported by the most OSes and hardware vendors.
• l2tp to connect over the Internet using the Layer Two Tunneling Protocol (L2TP). L2TP is a PPTP successor supported with modern clients and servers.
• pppoe to connect over an Ethernet port using the PPP-over-Ethernet (PPPoE) protocol. This protocol is often used by DSL providers.
• tcp to tunnel PPP session over a TCP connection. Frames are encoded in the same was as asychronous serial connections.
• udp to tunnel PPP session over a UDP connection. Each frame is encapsulated in a UDP datagram packet.
• ng to connect using different devices supported by netgraph. Netgraph is highly modular kernel networking system, supporting synchronous serial connections, Cisco HDLC, Frame Relay, and other protocols.

It supports numerous PPP sub-protocols and extensions, such as:

• Multi-link PPP
• PAP, CHAP, MS-CHAP and EAP authentication
• traffic compression (MPPC, Deflate, Predictor-1)
• traffic encryption (MPPE, DESE, DESE-bis)
• IPCP and IPV6CP parameter negotiation

Depending on configured rules and connection parameters mpd can operate as usual PPP client/server or forward connection unmodified to other host using any supported link type providing LAC/PAC/TSA functionality for building distributed access networks.

Mpd also includes many additional features:

• IPv4 and IPv6 support
• Telnet and HTTP control interfaces.
• Different authentication and accounting methods (RADIUS, PAM, script, file, ...)
• NetFlow traffic accounting
• Network address translation (NAT)
• Dial-on-demand with idle timeout
• Dynamic demand based link management (also known as ``rubber bandwidth'')
• Powerful chat scripting language for asynchronous serial ports
• Pre-tested chat scripts for several common modems and ISDN TAs
• Clean device-type independent design
• Comprehensive logging

Mpd was originally developed at Whistle Communications, Inc. for use in the Whistle InterJet. It is based on the original iij-ppp user-mode PPP code, though it has been completely rewritten since then. Mpd is now hosted on sourceforge.net MPD Project Page.