---
name: "nos-tun"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/nos-tun"
---

# nos-tun(8)

implement \`\`nos'' or \`\`ka9q'' style IP over IP tunnel

## NAME

**nos-tun** – implement \`\`nos'' or \`\`ka9q'' style IP over IP tunnel

## SYNOPSIS

**nos-tun** **-t** *tunnel* **-s** *source* **-d** *destination* **-p** *protocol\_number* \[*source*\] *target*

## DESCRIPTION

The **nos-tun** utility is used to establish an *nos* style tunnel, (also known as *ka9q* or *IP-IP* tunnel) using a [tun(4)](/tun/4.md) 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 “255.255.255.252” 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.

## EXAMPLES

This end, a FreeBSD box on address 192.168.59.34:

```
nos-tun -t /dev/tun0 -s 192.168.61.1 -d 192.168.61.2 192.168.56.45
```

Remote cisco on address 192.168.56.45:

```
interface tunnel 0
ip address 192.168.61.2 255.255.255.252
tunnel mode nos
tunnel destination 192.168.59.34
tunnel source 192.168.56.45
```

## HISTORY

The **nos-tun** utility appeared in FreeBSD 3.0.

## AUTHORS

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.

## BUGS

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