pppd

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Summary help replacing me
This article explains how to set up a point-to-point connections using pppd and the kernel PPPoE driver.

ppp (Paul's PPP Package) is an open source package which implements the point-to-point protocol (PPP) on Linux and Solaris systems. It is implemented as single pppd daemon and acts as backend for xl2tpd, pptpd and netcfg. 3G, L2TP and PPPoE connections are internally based on PPP protocol and therefore can be managed by ppp.

Installation

Install ppp, available in the official repositories.

Make sure that your kernel is compiled with PPPoE support (present in default kernel):

$ zgrep CONFIG_PPPOE /proc/config.gz
CONFIG_PPPOE=m

Configuration

PPPoE

Create the connection configuration file:

/etc/ppp/peers/your_provider
plugin rp-pppoe.so
# rp_pppoe_ac 'your ac name'
# rp_pppoe_service 'your service name'
  
# network interface
eth0
# login name
name "someloginname"
usepeerdns
persist
# Uncomment this if you want to enable dial on demand
#demand
#idle 180
defaultroute
hide-password
noauth

If you want usepeerdns to work, you have to edit your /etc/ppp/ip-up and add a command that copies /etc/ppp/resolv.conf to /etc/resolv.conf.

Edit /etc/ppp/pap-secrets:

Put a line like this in /etc/ppp/pap-secrets

someloginname * yourpassword

You can now start the link using the command

# pppd call your_provider

Alternatively, you can use this

# pon your_provider

By default the configuration in /etc/ppp/peers/provider is treated as the default, so if you want to make "your_provider" the default, you can create a link like this

# ln -s /etc/ppp/peers/your_provider /etc/ppp/peers/provider

Now you can start the link by simply running

# pon

To close a connection, use this

# poff your_provider

Starting pppd with Arch

  • The init script /etc/rc.d/ppp calls the default ppp provider (/etc/ppp/peers/provider), so make sure you have the right configuration file there, otherwhise you could create a symlink to the desired provider as explained before.
  • Make sure ppp module is loaded. If ppp support is compiled as a module, you have to load the ppp_generic module. In this case, add this to rc.conf:
MODULES=(... ppp-generic ...)
  • Add ppp to DAEMONS in /etc/rc.conf, and make sure that you also have the network daemon listed:
DAEMONS=(... network ... ppp ...)
  • Also make sure that you have the correct interface declared in the networking section of /etc/rc.conf.

Troubleshooting

Default route

If you have a preconfigured default route before the pppd is started, the default route is kept, so take a look in /var/log/errors.log and if you have something like:

pppd[nnnn]: not replacing existing default route via xx.xx.xx.xx

and xx.xx.xx.xx is not the correct route for you

  • Create a new script /etc/ppp/ip-pre-up
$ chmod +x /etc/ppp/ip-pre-up

with this content:

#!/bin/sh
/sbin/route del default
  • Restart pppd:
$ /etc/rc.d/ppp restart

Masquering seems to be working fine but some sites don't work.

The MTU under pppoe is 1492 bytes. Most sites use an MTU of 1500. So your connection sends an ICMP 3:4 (fragmentation needed) packet, asking for a smaller MTU, but some sites have their firewall blocking that.

Using PMTU clamping can solve that:

iptables -I FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu