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Manual Pages  — NOS-TUN


nos-tun – implement ``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


The nos-tun utility appeared in FreeBSD 3.0 .


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


We do not allow for setting our source address for multihomed machines.

NOS-TUN (8) October 5, 2016

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