MAP66 (NAT from IPv6 to IPv6, NAT66) for Linux

These files implement a Linux netfilter target that changes the IPv6 address of packets. The address change is done checksum neutral, thus no checksum re-calculation for the packet is necessary. You can change the IPv6 source address of outgoing packets as well as the IPv6 destination address @@ -8,19 +8,21 @@ to a second, externally used IPv6 address range. IPv6 address mapping is not very similar to IPv4 network address translation, but one can describe it as some sort of stateless NAT. The implementation is based on the expired IETF - discussion paper published here:

http://tools.ietf.org/html/draft-mrw-behave-nat66-02

Warning

Using MAP66 rules together with connection tracking rules such as + discussion paper published here:

https://tools.ietf.org/html/rfc6296

Warning

Using NPTv6 rules together with connection tracking rules such as --ctstate is currently untested and may not work or - may cause dysfunctions.

Installation

MAP66 implements two pieces of software: a shared library that + may cause dysfunctions.

Installation

NPTv6 implements two pieces of software: a shared library that extends the ip6tables command and a Linux kernel module. The shared - library file adds the '-j MAP66' target to the ip6tables command. To build - and install, you need ip6tables installed as well as the necessary - headers. The Linux kernel module requires the Linux source file tree and - kernel configuration files to compile. On a Debian/(EKU)buntu, the - following command prepares the build environment:

sudo apt-get install build-essential linux-headers iptables-dev

Unpack the source tgz archive below /usr/src, + library file adds the '-j SNPTV6' target (for source address translation) + and the '-j DNPTV6' target (for destination address translation) to the + ip6tables command. To build and install, you need ip6tables installed as + well as the necessary headers. The Linux kernel module requires the Linux + source file tree and kernel configuration files to compile. On a Debian/(EKU)buntu, + the following command prepares the build environment:

sudo apt-get install build-essential linux-headers iptables-dev

Unpack the source tgz archive below /usr/src, change to the new sub-directory and issue "make" to build. If this - compiles without errors, install the ip6tables extension with the - following command:

sudo make install

Note

The kernel module (ip6t_MAP66.ko for - Linux-2.6 or ip6t_MAP66.o for Linux-2.4) is not + compiles without errors, install the ip6tabless extension by copying + libip6t_SNPTV6.so and libip6t_DNPTV6.so to the iptables module directory, + which is probably located under /lib/xtables or + /usr/lib/iptables.

Note

The kernel module (ip6t_MAP66.ko is not automatically installed nor loaded into the kernel. You can copy the kernel module file manually, e.g. with sudo cp ip6t_MAP66.ko /lib/modules/$(uname -r)/.

DKMS Integration

If the next system update needs to install a new kernel version, you @@ -30,94 +32,17 @@ file is included with the MAP66 source file package. Install DKMS with the following command:

sudo apt-get install dkms

If not already in place, move/unpack the MAP66 source file archive below /usr/src/. To register the MAP66 source to DKMS - and compile/install, issue these commands:

sudo dkms add -m ip6t_MAP66 -v 0.5
-sudo dkms build -m ip6t_MAP66 -v 0.5
-sudo dkms install -m ip6t_MAP66 -v 0.5

Read DKMS details here: https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging

Configuration

Brief Version

You always need to add two ip6tables-rules to your netfilter + and compile/install, issue these commands:

sudo dkms add -m ip6t_NPTV6 -v 0.6
+sudo dkms build -m ip6t_NPTV6 -v 0.6
+sudo dkms install -m ip6t_NPTV6 -v 0.6

Read DKMS details here: https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging

Configuration

Brief Version

You always need to add two ip6tables-rules to your netfilter configuration. One rule matches outgoing packets and changes their IPv6 source address. The second rule matches incoming packets and reverts the address change by altering their IPv6 destination address. To following commands correspond to the “Address Mapping Example” given - in the IETF discussion paper:

ip6tables -t mangle -I POSTROUTING -o eth0 -s FD01:0203:0405::/48 -j MAP66 --src-to 2001:0DB8:0001::/48
-ip6tables -t mangle -I PREROUTING  -i eth0 -d 2001:0DB8:0001::/48 -j MAP66 --dst-to FD01:0203:0405::/48

This example is also printed to the screen if you issue - ip6tables -j MAP66 --help. By design, you cannot - use an arbitrary prefix length. Only /112, /96 .. /16 are - supported.

For each packet, the Linux kernel module also compares the - packet's source address to all IPv6 addresses assigned to the outgoing - interface. If a match is found, the packet's source address is not - mapped. The same comparison happens on the incoming packet's destination - address. The comparison requires some CPU resources, especially if the - interface has a large number of assigned IPv6 addresses. If you are sure - that the mapping cannot match the IPv6 address of the interface (e.g. - the mapping rule defines a mapping prefix that cannot result in the - interface address) you can switch off the comparison. Add the - --nocheck parameter to the ip6tables command for - this.

Detailed Version

The following explanation details a living example from the - wireless mesh network that is mentioned under Motivation (see below). - Throughout the mesh network, a private IP address range is used. The ULA - prefix is fdca:ffee:babe::/64. All mesh nodes derive their IPv6 - interface addresses by correlating the ULA prefix with the EUI48 - (“MAC address”) of the respective network adapter.

There is a Debian based virtual machine that should act as one - IPv6 Internet gateway for the mesh. You can reach the virtual machine's - web service via IPv4 under http://bbb-vpn.freifunk.net. - To experiment with IPv6, a SIXXS static tunnel setup has been - added and there is also an experimental 6-to-4 configuration. The - following /etc/network/interfaces file provides the - configuration for IPv6:

auto sixxs
-iface sixxs inet6 v4tunnel
-        address  2001:4dd0:ff00:2ee::2
-        netmask 64
-        local 77.87.48.7
-        endpoint 78.35.24.124
-        ttl 64
-        up ip link set mtu 1280 dev $IFACE
-        up ip route add default via  2001:4dd0:ff00:2ee::1 dev $IFACE
-        up ip addr add 2001:4dd0:fe77::1/48 dev $IFACE
-
-#auto tun6to4
-iface tun6to4 inet6 v4tunnel
-        # ipv6calc --quiet --action conv6to4 77.87.48.7
-        address 2002:4d57:3007::1
-        netmask 16
-        local 77.87.48.7
-        endpoint any
-        ttl 64
-        gateway ::192.88.99.1

As you can see, the virtual machine has an IPv6 prefix of - 2001:4dd0:fe77::/48 and is reachable via http://[2001:4dd0:fe77::1]/. - For experimental purposes, the 6-to-4 tunnel can be activated by issuing - ifup tun6to4. The netfilter setup of this machine - includes the following command sequence to realize mapping from the - private fdca:ffee:babe::/64 prefix to the globally valid IPv6 - addresses:

ip6tables -t mangle -F POSTROUTING
-ip6tables -t mangle -F PREROUTING
-ip6tables -t mangle -F FORWARD
-
-grep -q ^ip6t_MAP66 /proc/modules && rmmod ip6t_MAP66
-insmod /usr/src/map66/ip6t_MAP66.ko
-
-ip6tables -t mangle -A POSTROUTING -o sixxs -s fdca:ffee:babe::/64 -j MAP66 --src-to 2001:4dd0:fe77:1::/64 --nocheck
-ip6tables -t mangle -A PREROUTING  -i sixxs -d 2001:4dd0:fe77:1::/64 -j MAP66 --dst-to fdca:ffee:babe::/64 --nocheck
-ip6tables -t mangle -A POSTROUTING -o tun6to4 -s fdca:ffee:babe::/64 -j MAP66 --src-to 2002:4d57:3007:1::/64 --nocheck
-ip6tables -t mangle -A PREROUTING  -i tun6to4 -d 2002:4d57:3007:1::/64 -j MAP66 --dst-to fdca:ffee:babe::/64 --nocheck
-ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

Because for both IPv6 networks the external prefix length is - smaller than the internal prefix length, we can make sure that the - mapped addresses cannot match the interface addresses. For example: - 2001:4dd0:fe77:1::/64 cannot be converted to 2001:4dd0:fe77:0::1/128 in - this context. For this reason, we can use the - --nocheck speedup here.

You may stumble over the MSS-clamping rule. While IPv6 defines, - that path MTU detection via ICMPv6 must be supported by any host, - sometimes path MTU detection does not work. The SIXXS tunnel uses an MTU - of 1280 byte. To get the following command working on my PC, I needed to - add the above MSS-clamping rule on the gateway:

wget --prefer-family=IPv6 -O - http://6to4.nro.net/

Note

The tun6to4 tunnel interface is disabled normally, because of - the implicit 2002::/16 network route configured for that interface. - This network route ensures, that traffic between one 2002::/16 to - another 2002::/16 travels directly between the IPv4 hosts. Without - this network route, any IPv6 traffic will be routed via the 6-to-4 - gateways which may not work and place a higher load on those 6-to-4 - gateways.

However, if you ping the SIXXS IP address from another host that - has a 6-to-4 address, you will get the answer packet back via the - 6-to-4 interface. If the above address mapping is configured, you ping - one IPv6 address and get the answer from another IPv6 - address...

IPv6/IPv4 Precedence

With (EKU)buntu and eventually with RedHat, you will notice that + in the IETF discussion paper:

ip6tables -t mangle -I POSTROUTING -o eth0 -s FD01:0203:0405::/48 -j SNPTV6 --to-source 2001:0DB8:0001::/48
+ip6tables -t mangle -I PREROUTING  -i eth0 -d 2001:0DB8:0001::/48 -j DNPTV6 --to-destination FD01:0203:0405::/48

This example is also printed to the screen if you issue + ip6tables -j SNPTV6 --help. By design, you cannot + use prefix lengths longer than 64.

IPv6/IPv4 Precedence

With (EKU)buntu and eventually with RedHat, you will notice that your browser does not show the IPv6 version of a web site that is multi-homed when using ULA addresses for your IPv6 Internet connection. The reason for this is an add on to the RFC 3484 rules that is compiled @@ -135,7 +60,7 @@ ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp- you cannot uncomment a single entry to overwrite the default. You need to uncomment all entries of a particular type for this. The “label” lines compare source addresses, the - “precedence” lines compare destination addresses.

Procedure 1. Change IPv6 Precedence

Open the /etc/gai.conf file as root user, + “precedence” lines compare destination addresses.
Procedure 1. Change IPv6 Precedence
1. Open the /etc/gai.conf file as root user, e.g. by executing sudo nano /etc/gai.conf.
2. Remove the leading hash character from the 8 lines starting with “#label”.
3. Re-add the hash character to the line stating “#label @@ -153,7 +78,7 @@ ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp- 6to4 addresses also.
If you already deployed ULA addresses in your network, you may be interested in a solution that runs on my Freifunk router. The router uses the IPv6 prefix that is reserved for documentation purposes on it's - LAN interface. WIthin the OLSR-based mesh network, any interface uses an + LAN interface. Within the OLSR-based mesh network, any interface uses an fdca:ffee:babe::/64 prefix. The following internal mapping is configured for this:
```
ip6tables -t mangle -I PREROUTING -i br0 -s 2001:0DB8::/64 -j MAP66 --src-to fdca:ffee:babe::/64 --csum
 ip6tables -t mangle -I POSTROUTING -o br0 -d fdca:ffee:babe::/64 -j MAP66 --dst-to 2001:0DB8::/64 --csum
```
To prevent the mapped packets to vanish via the default route and -- cgit v1.2.3