Pfinet is a TCP/IP stack from an old linux version. It works but is not maintained. Recently Recently lwip, which is an userspace tcp/ip library, was ported to the Hurd, which can serve as a direct replacement for pfinet.

To configure Internet connectivity, the pfinet (Protocol Family Internet) translator must be configured. This is done using the settrans command, for example like this:

# settrans -fgap /servers/socket/2 /hurd/pfinet ↩
    -i eth0 -a -g -m

The argument /server/socket/2 is the node that the translator is to be attached to. This is followed by the translator program to run and any arguments to give it.

There, -i, -a, -g and -m are, quite obviously, the (Mach) device to use, the IP address, the gateway and netmask.

To make DNS lookups work, you'll also have to properly configure the /etc/resolv.conf file, for example by copying it over from your GNU/Linux installation.