The Care and Feeding of ISDN4BSD
11.3 isdnd.rc Setup	11 Setting up an	11.5 Troubleshooting

11.4 ipr0 Setup in /etc/rc.conf

The configuration of the ipr0 interface is done at system startup time using the normal FreeBSD mechanism using the /etc/rc.conf database. The section for my gateway looks like this:

network_interfaces="ed0 lo0 ipr0"

# List of network interfaces (lo0 is loopback).

ifconfig_ed0="inet 123.45.67.8 netmask 255.255.255.0"

ifconfig_lo0="inet 127.0.0.1" # default loopback device configuration.

# => provider

ifconfig_ipr0="inet 123.45.67.8 234.56.78.9 netmask 255.255.255.255"

This all looks quite usual - with one exception: the ipr0 interface gets the same IP address as this machine's Ethernet interface. This is a legal thing to do and very convenient because it simplifies things very much.