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userland-ipip

Userland IPIP + IP6IP (6in4) / IPIP6 + IP6IP6 tunnel for Linux

userland-ipip sets up either an IPIP + IP6IP (6in4) tunnel, or an IPIP6 + IP6IP6 tunnel between two hosts.

Features

  • userland-ipip reduces headache when you find that a type ip6tnl mode any tunnel is not as reliable as you assume. Either IPv4 or IPv6 payload drops silently at some magic time. You tried various methods, only to find that a system reboot can solve the problem auto-magically.

  • userland-ipip calculates local address automatically, saving you time to write scripts for an DHCP-assigned host.

  • userland-ipip also solves the problem when you want to fragment your tunnel. (i.e. inner MTU larger than outer MTU.)

Building

  1. Download Go compiler. The newer version, the better.

  2. Type

./build.sh
  1. Pick your fruit at ./build/ipip.

Usage

Usage: ipip [-4 | -6] dev DEVICE [local ADDRESS] remote ADDRESS [mtu MTU]
Userland IPIP + IP6IP (6in4) / IPIP6 + IP6IP6 tunnel for Linux.

This program establishes IPIP and IP6IP (6in4) tunnel, or IPIP6 and IP6IP6
tunnel on a TUN device.

Options:
  -4            use IPv4 to resolve addresses.
  -6            use IPv6 to resolve addresses.
                  otherwise, IPv6 will be tried first, then IPv4.

Project web page: https://github.com/m13253/userland-ipip

Example

Please change the names and the addresses below to suit your needs.

On the first machine (e.g. fox.localdomain)

sudo ip tuntap add mode tun name tun-rabbit
sudo ip address add 10.0.0.1 peer 10.0.0.2/32 dev tun-rabbit
sudo ip address add fd00:cafe::1 peer fd00:cafe::2/128 dev tun-rabbit
sudo ./build/ipip dev tun-rabbit remote rabbit.localdomain mtu 1460

On the second machine (e.g. rabbit.localdomain)

sudo ip tuntap add mode tun name tun-fox
sudo ip address add 10.0.0.2 peer 10.0.0.1/32 dev tun-fox
sudo ip address add fd00:cafe::2 peer fd00:cafe::1/128 dev tun-fox
sudo ./build/ipip dev tun-fox remote fox.localdomain mtu 1460

To stop the tunnel, press Ctrl-C, then type

sudo ip link delete tun-rabbit

or

sudo ip link delete tun-fox

Preventing “connection refused”

You may find a lot of “connection refused” on the screen. They are caused by the remote machine sending ICMP errors to us.

It is suggested to block these packets to save bandwidth. A dirty but effective method is to use iptables on both sides running userland-ipip:

sudo iptables -A OUTPUT -d [PEER IPv4 ADDRESS] -p icmp --icmp-type 3/3 -j DROP
sudo ip6tables -A OUTPUT -d [PEER IPv6 ADDRESS] -p icmpv6 --icmpv6-type 1/4 -j DROP

Use userland-ipip with systemd

I don't provide a systemd service file out-of-the-box, since you may want to write one systemd service for each tunnel you want to create.

Here is a template that you can modify based on:

[Unit]
Description=Userland IPIP for rabbit.localdomain
Documentation=https://github.com/m13253/userland-ipip
After=network.target

[Service]
ExecStartPre=-/usr/bin/env ip tunnel delete tun-rabbit
ExecStartPre=/usr/bin/env ip tuntap add mode tun name tun-rabbit
ExecStartPre=/usr/bin/env ip address add 10.0.0.1 peer 10.0.0.2/32 dev tun-rabbit
ExecStartPre=/usr/bin/env ip address add fd00:cafe::1 peer fd00:cafe::2/128 dev tun-rabbit
ExecStart=/path/to/ipip dev tun-rabbit local fox.localdomain remote rabbit.localdomain mtu 1460
ExecStopPost=/usr/bin/env ip tunnel delete tun-rabbit
Restart=always
RestartSec=3
Type=simple

[Install]
WantedBy=multi-user.target

Use userland-ipip with /etc/network/interfaces

auto tun-rabbit
iface tun-rabbit inet static
    address 10.0.0.1
    pointopoint 10.0.0.2
    pre-up ip tuntap add mode tun name $IFACE
    up /path/to/ipip dev $IFACE local fox.localdomain remote rabbit.localdomain mtu 1460 &
    post-down ip link del $IFACE
iface tun-rabbit inet6 static
    address fd00:cafe::1/128
    up ip route add fd00:cafe::2 dev $IFACE metric 256

License

This program is released under GNU General Public License version 3 or later. I hope this program can be useful to you. But I provide absolutely no warranty. In case the program causes any damage due to malfunctioning, I might be willing to diagnose and fix the problem, but it is not my obligation to do so.