
=pod

=head1 NAME

B<parprouted> - Proxy ARP IP bridging daemon

=head1 SYNOPSIS

B<parprouted> [B<-d>] [B<-p>] B<interface> [B<interface>]

=head1 DESCRIPTION

parprouted is a daemon for transparent IP (Layer 3) proxy ARP bridging. 
Unlike standard bridging, proxy ARP bridging allows to bridge Ethernet 
networks behind wireless nodes. Normal L2 bridging does not work between 
wireless nodes because wireless does not know about MAC addresses used 
in the wired Ethernet networks. Also this daemon is useful
for making transparent firewalls.

The daemon listens for incoming ARP requests, and in case the location 
of the requested IP address is unknown, forwards them to other interfaces, 
as well as updates kernel ARP table with the received replies. When 
necessary, the daemon generates an ARP reply itself, which causes the 
stations to send traffic to the host daemon is running on. By 
automatically adding appropriate /32 routes to Linux kernel IP routing 
table for the hosts learned via ARP, daemon ensures that the Linux kernel 
will be able to route the packets to the destination host when it receives 
them without any need routing/subnetting manually.  

All routes entered by the daemon have a metric of 50. 

Unless you use B<-p> switch, all entries in the ARP table will be
refreshed (rechecked by sending ARP requests) every 50 seconds. This
keeps them from being expired by kernel.

Normally it takes about 60 ms for a bridge to update all its tables and
start sending packets to the destination.

=head1 REQUIREMENTS

This daemon can be used for unicast traffic only. I.e., DHCP is not supported.
Use software such as dhcrelay to "bridge" DHCP.

You should have an IP address assigned on all of your interfaces that you do 
bridging on. There is no need for this address to be from the same networks as 
the bridged networks. Any dummy address will do.

The system should have correct default route.

parprouted requires "ip" program from iproute2 tools to be installed in 
/sbin. If it is installed in another location, please replace "/sbin/ip" 
occurances in the source with the correct path. As well you should have
proc filesystem mounted in /proc because the daemon uses /proc/net/arp.

parprouted is designed for and tested only with Linux 2.4.x kernels.

=head1 OPTIONS

The list of interfaces to do bridging on should be given via the command
line.

The daemon accepts the following switches:

B<-d>, which stands for debugging. If you run it in debugging mode the daemon 
will not go to background and will print additional debugging information to 
stdout/stderr.

B<-p>, which makes all ARP entries to be permanent. This will also
result in that ARP tables will not be refreshed by ARP pings.

=head1 EXAMPLE

To bridge between wlan0 and eth0: B<parprouted eth0 wlan0>

=head1 AUTHOR

 (C) 2008, Vladimir Ivaschenko <vi@maks.net>
 http://www.hazard.maks.net
