The Care and Feeding of ISDN4BSD
10.4.3 Using tcpdump	The Care and Feeding	11.1 Encapsulation Format

11 Setting up an IP over raw HDLC Link (ipr)

This section deals with the ipr network interfaces which are - like the PPP interfaces - used to setup an IP link between two systems, just the encapsulation of the IP frames differs. And it is much easier and less problematic to setup.