NOS-TUN(8) FreeBSD System Manager's Manual NOS-TUN(8)


nos-tunimplement ``nos'' or ``ka9q'' style IP over IP tunnel


nos-tun -t tunnel -s source -d destination -p protocol_number [ source] target


The nos-tun utility is used to establish an nos style tunnel, (also known as ka9q or IP-IP tunnel) using a tun(4) kernel interface.

Tunnel is the name of the tunnel device /dev/tun0 for example.

Source and destination are the addresses used on the tunnel device. If you configure the tunnel against a cisco router, use a netmask of “” on the cisco. This is because the tunnel is a point-to-point interface in the FreeBSD end, a concept cisco does not really implement.

Protocol number sets tunnel mode. Original KA9Q NOS uses 94 but many people use 4 on the worldwide backbone of ampr.org.

Target is the address of the remote tunnel device, this must match the source address set on the remote end.


This end, a FreeBSD box on address

nos-tun -t /dev/tun0 -s -d

Remote cisco on address

interface tunnel 0 
ip address 
tunnel mode nos 
tunnel destination 
tunnel source


Nickolay N. Dudorov <nnd@itfs.nsk.su> wrote the program, Poul-Henning Kamp <phk@FreeBSD.org> wrote the man-page. Isao SEKI <iseki@gongon.com> added a new flag, IP protocol number.


We do not allow for setting our source address for multihomed machines.
April 11, 1998 FreeBSD