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| author | sven-ola <sven-ola@3484d885-4da6-438d-b19d-107d078dd756> | 2010-10-06 18:40:53 +0200 |
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| committer | sven-ola <sven-ola@3484d885-4da6-438d-b19d-107d078dd756> | 2010-10-06 18:40:53 +0200 |
| commit | adbd402d7074652fe5b041d77b4ddef1f8c3ab3a (patch) | |
| tree | cb7d28e0043f0951cd55a290a1c2d29b89c5e8ea /README.html | |
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diff --git a/README.html b/README.html new file mode 100644 index 0000000..d46221a --- /dev/null +++ b/README.html @@ -0,0 +1,170 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>MAP66 (NAT from IPv6 to IPv6, NAT66) for Linux</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /></head><body><div class="article" title="MAP66 (NAT from IPv6 to IPv6, NAT66) for Linux"><div class="titlepage"><div><div><h2 class="title"><a id="id2928121"></a>MAP66 (NAT from IPv6 to IPv6, NAT66) for Linux</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Sven-Ola</span> <span class="surname">Tuecke</span></h3><div class="affiliation"><span class="orgname">Freifunk<br /></span></div></div></div><div><p class="pubdate">06-OCT-2010</p></div></div><hr /></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id2961474">Installation</a></span></dt><dt><span class="section"><a href="#id2953819">DKMS Integration</a></span></dt><dt><span class="section"><a href="#id2974647">Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#id2959435">Brief Version</a></span></dt><dt><span class="section"><a href="#id2955411">Detailed Version</a></span></dt></dl></dd><dt><span class="section"><a href="#id2949227">IPv6/IPv4 Precedence</a></span></dt><dt><span class="section"><a href="#motivation">Motivation</a></span></dt></dl></div><p>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 + of incoming packets. This allows you to map an internal IPv6 address range + 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:</p><p><a class="ulink" href="http://tools.ietf.org/html/draft-mrw-behave-nat66-02" target="_top">http://tools.ietf.org/html/draft-mrw-behave-nat66-02</a></p><div class="section" title="Installation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2961474"></a>Installation</h2></div></div></div><p>MAP66 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:</p><pre class="programlisting">sudo apt-get install build-essential linux-headers iptables-dev</pre><p>Unpack the source tgz archive below <code class="filename">/usr/src</code>, + change to the new sub-directory and issue "make" to build. If this + compiles without errors, install the ip6tables extension with the + following command:</p><pre class="programlisting">sudo make install</pre><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The kernel module (<code class="filename">ip6t_MAP66.ko</code> for + Linux-2.6 or <code class="filename">ip6t_MAP66.o</code> for Linux-2.4) is not + automatically installed nor loaded into the kernel. You can copy the + kernel module file manually, e.g. with <strong class="userinput"><code>sudo cp ip6t_MAP66.ko + /lib/modules/$(uname -r)/</code></strong>.</p></div></div><div class="section" title="DKMS Integration"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2953819"></a>DKMS Integration</h2></div></div></div><p>If the next system update needs to install a new kernel version, you + also need to re-compile/re-install the MAP66 kernel module. With + Debian/(EKU)buntu, this can be automated with the Dynamic Kernel Module + Support Framework (DKMS). For this, the <code class="filename">dkms.conf</code> + file is included with the MAP66 source file package. Install DKMS with the + following command:</p><pre class="programlisting">sudo apt-get install dkms</pre><p>If not already in place, move/unpack the MAP66 source file archive + below <code class="filename">/usr/src/</code>. To register the MAP66 source to DKMS + and compile/install, issue these commands:</p><pre class="programlisting">sudo dkms add -m ip6t_MAP66 -v 0.3 +sudo dkms build -m ip6t_MAP66 -v 0.3 +sudo dkms install -m ip6t_MAP66 -v 0.3</pre><p>Read DKMS details here: <a class="ulink" href="Read DKMS details here: https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging" target="_top">https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging</a></p></div><div class="section" title="Configuration"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2974647"></a>Configuration</h2></div></div></div><div class="section" title="Brief Version"><div class="titlepage"><div><div><h3 class="title"><a id="id2959435"></a>Brief Version</h3></div></div></div><p>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 <span class="quote">“<span class="quote">Address Mapping Example</span>”</span> given + in the IETF discussion paper:</p><pre class="programlisting">ip6tables -t mangle -I POSTROUTING -o eth0 -s FD01:0203:0405::/48 -j MAP66 --to 2001:0DB8:0001::/48 +ip6tables -t mangle -I PREROUTING -i eth0 -d 2001:0DB8:0001::/48 -j MAP66 --to FD01:0203:0405::/48</pre><p>This example is also printed to the screen if you issue + <strong class="userinput"><code>ip6tables -j MAP66 --help</code></strong>. By design, you cannot + use an arbitrary prefix length. Only /112, /96 .. /16 are + supported.</p><p>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 + <strong class="userinput"><code>--nocheck</code></strong> parameter to the ip6tables command for + this.</p></div><div class="section" title="Detailed Version"><div class="titlepage"><div><div><h3 class="title"><a id="id2955411"></a>Detailed Version</h3></div></div></div><p>The following explanation details a living example from the + wireless mesh network that is mentioned under <a class="xref" href="#motivation" title="Motivation">Motivation</a> (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 + (<span class="quote">“<span class="quote">MAC address</span>”</span>) of the respective network adapter.</p><p>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 <a class="ulink" href="http://bbb-vpn.freifunk.net" target="_top">http://bbb-vpn.freifunk.net</a>. + To experiment with IPv6, a <a class="ulink" href="http://www.sixxs.net/" target="_top">SIXXS</a> static tunnel setup has been + added and there is also an experimental 6-to-4 configuration. The + following <code class="filename">/etc/network/interfaces</code> file provides the + configuration for IPv6:</p><pre class="programlisting">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</pre><p>As you can see, the virtual machine has an IPv6 prefix of + 2001:4dd0:fe77::/48 and is reachable via <a class="ulink" href="http://[2001:4dd0:fe77::1]/" target="_top">http://[2001:4dd0:fe77::1]/</a>. + For experimental purposes, the 6-to-4 tunnel can be activated by issuing + <strong class="userinput"><code>ifup tun6to4</code></strong>. 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:</p><pre class="programlisting">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 --to 2001:4dd0:fe77:1::/64 --nocheck +ip6tables -t mangle -A PREROUTING -i sixxs -d 2001:4dd0:fe77:1::/64 -j MAP66 --to fdca:ffee:babe::/64 --nocheck +ip6tables -t mangle -A POSTROUTING -o tun6to4 -s fdca:ffee:babe::/64 -j MAP66 --to 2002:4d57:3007:1::/64 --nocheck +ip6tables -t mangle -A PREROUTING -i tun6to4 -d 2002:4d57:3007:1::/64 -j MAP66 --to fdca:ffee:babe::/64 --nocheck +ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu</pre><p>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 + <strong class="userinput"><code>--nocheck</code></strong> speedup here.</p><p>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:</p><pre class="programlisting">wget --prefer-family=IPv6 -O - http://6to4.nro.net/</pre><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>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.</p><p>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...</p></div></div></div><div class="section" title="IPv6/IPv4 Precedence"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2949227"></a>IPv6/IPv4 Precedence</h2></div></div></div><p>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 + into the (EKU)buntu libc. The pre-installed + <code class="filename">/etc/gai.conf</code> file will give you a hint on + this.</p><p>In short: the getaddrinfo() library function rates a private IPv4 + address higher than the ULA IPv6 address when choosing the transport + protocol for a new Internet connection if this add on to the RFC 3484 + rules is compiled in. For this reason, you may want to change the + precedence rules within <code class="filename">/etc/gai.conf</code>.</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The getaddrinfo() library function manages lists of label, + precedence, and scope4 type entries. If the + <code class="filename">/etc/gai.conf</code> file does not provide a single entry + for a particular type, the compiled-in list is used. For this reason, + you cannot uncomment a single entry to overwrite the default. You need + to uncomment all entries of a particular type for this. The + <span class="quote">“<span class="quote">label</span>”</span> lines compare source addresses, the + <span class="quote">“<span class="quote">precedence</span>”</span> lines compare destination addresses.</p></div><div class="procedure" title="Procedure 1. Change IPv6 Precedence"><a id="id2955439"></a><p class="title"><b>Procedure 1. Change IPv6 Precedence</b></p><ol class="procedure" type="1"><li class="step" title="Step 1"><p>Open the <code class="filename">/etc/gai.conf</code> file as root user, + e.g. by executing <strong class="userinput"><code>sudo nano + /etc/gai.conf</code></strong>.</p></li><li class="step" title="Step 2"><p>Remove the leading hash character from the 8 lines starting with + <span class="quote">“<span class="quote">#label</span>”</span>.</p></li><li class="step" title="Step 3"><p>Re-add the hash character to the line stating <span class="quote">“<span class="quote">#label + fc00::/7 6</span>”</span>.</p></li><li class="step" title="Step 4"><p>Save the file.</p></li><li class="step" title="Step 5"><p>Restart your browser and re-try to browse to a multi-homed web + site.</p></li></ol></div><p>The above procedure removes the difference between standard IPv6 + source addresses and ULA type private IPv6 source addresses. Anything else + is unchanged.</p></div><div class="section" title="Motivation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="motivation"></a>Motivation</h2></div></div></div><p>My Internet access at home is realized by a wireless community mesh + network not owned by me. The mesh is operated with small embedded devices + (nodes aka. WLAN routers) that are interconnected via radio links (WLAN + IBSS / AdHoc). Routing is done with a specialized protocol such as Batman + or OLSR. The routing protocol selects the nearest out of a dozen Internet + gateways and configures a default route or an IPIP tunnel accordingly. + Each Internet gateway is connected to a different ISP and provides the + service with the help of IPv4 network address translation (NAT). Using NAT + has the following effects:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Address amplification - something not necessary with IPv6 any + more</p></li><li class="listitem"><p>Anonymization - nice to have as an option but not mission + critical</p></li><li class="listitem"><p>ISP independence - no reverse routing, no + "buy-a-number-range"</p></li></ul></div><p>The last point <span class="bold"><strong>is</strong></span> mission critical. + One can obtain a provider independent IPv6 address range, but you need the + cooperation of an ISP to use that address range for Internet connectivity. + If you e.g. move to another ISP you need your address range to be + re-routed to your new location.</p><p>ISP independence is also possible with some tunneling technique, + such as VPN or mobile IP. Tunneling can be implemented on client PCs and + Internet gateways/servers one day. But there is no need to implement the + same tunneling technique on every mesh node. Why? Because the mesh nodes + can use private IP addresses (or "ULA") to transport the tunnel data + between the client PC and the gateway/server. Each tunneling technique + typically needs a single instance (the "server") which forms a single + point of failure. Rule-of-thumb1: avoid a SPOF for the infrastructure. + Rule-of-thumb2: KISS (keep it simple stupid).</p><p>Using private IP addresses on the mesh nodes has a drawback: mesh + node software updates e.g. a download via HTTP from an Internet server is + not possible. This is where I start to think: <span class="quote">“<span class="quote">hey, some kind of + address mapping may be nice to have</span>”</span>. While opening Pandora's NAT66 + box, I discovered that IPv6 nerds do not like the acronym. It is always a + good tactic in info wars to rename, hence the name "MAP66".</p><p>// Sven-Ola</p></div></div></body></html> |