more doc

git-svn-id: https://map66.svn.sourceforge.net/svnroot/map66@6 3484d885-4da6-438d-b19d-107d078dd756

1 files changed, 129 insertions, 28 deletions

diff --git a/README.txt b/README.txt
index 4aced05..eaf36f2 100644
--- a/README.txt
+++ b/README.txt
@@ -11,8 +11,13 @@ Freifunk
 Table of Contents
 
 Installation
-DKMS integration
+DKMS Integration
 Configuration
+
+    Brief Version
+    Detailed Version
+
+Hints (Chapter is To-do)
 Motivation
 
 These files implement a Linux netfilter target to change the IPv6 address of
@@ -22,7 +27,7 @@ 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 implmementation is based on the expired the IETF discussion
+stateless NAT. The implementation is based on the expired the IETF discussion
 paper published here:
 
 http://tools.ietf.org/html/draft-mrw-behave-nat66-02
@@ -51,7 +56,7 @@ 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
+DKMS Integration
 
 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
@@ -62,8 +67,8 @@ Install DKMS with the following command:
 sudo apt-get install dkms
 
 Move/unpack the MAP66 source files below /usr/src and adapt the directory name
-to the version mentioned in the dkms.conf file. For example, issue "mkdir /usr/
-src/ip6t_MAP66-0.3" and "cp * /usr/src/ip6t_MAP66-0.3/". To register the MAP66
+to the version mentioned in the dkms.conf file. For example, issue mkdir /usr/
+src/ip6t_MAP66-0.3 and cp * /usr/src/ip6t_MAP66-0.3/. To register the MAP66
 source to DKMS and compile/install, issue these commands:
 
 sudo dkms add -m ip6t_MAP66 -v 0.3
@@ -74,36 +79,132 @@ Read DKMS details here: https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging
 
 Configuration
 
-Note for me: svn propedit svn:ignore.
+Brief Version
+
+You always need to add two ip6tables-rules to your netfilter configuration. One
+rule matches the outgoing packet and changes the IPv6 source address. The
+second rule matches the incoming packet and revert the address change by
+altering the 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 --to 2001:0DB8:0001::/48
+ip6tables -t mangle -I PREROUTING  -i eth0 -d 2001:0DB8:0001::/48 -j MAP66 --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. It 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 require 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 match
+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). The mesh network uses a
+private IP range, the ULA prefix 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 Internet gateway
+for the mesh. You can reach this 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 reasons, the
+6-to-4 tunnel can be activated by issuing ifup tun6to4. The netfilter setup of
+this machine includes the following command sequence to ensure mapping from the
+private fdca:ffee:babe::/64 prefix to the globally valid IPv6 address:
+
+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
+
+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 interfaces address. For example: 2001:4dd0:fe77:1::/64 cannot match
+2001:4dd0:fe77:0::1/128. For this reason, we can use the --nocheck speedup flag
+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, I needed to add the above MSS-clamping rule on the
+gateway:
+
+wget --prefer-family=IPv6 -O - http://6to4.nro.net/
 
-Note: on ubuntu, you need to enable prefer-family in /etc/wgetrc. after this
-e.g. "wget -O /dev/null http://ftp.se.debian.org" should connect to the IPv6
-addrs of that server.
+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 gateways.
 
-/etc/gai.conf
+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 6-to-4. If the above network
+mapping is configured, you ping one IPv6 address and get the answer from
+another IPv6 address...
 
-for wget --prefer-family=IPv6 -O - http://6to4.nro.net/ one needs ip6tables -t
-mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
+Hints (Chapter is To-do)
 
-Mention --nocheck for speedup (if you do not expect the outer iface in the
-mapping range)
+Note for me: svn propedit svn:ignore.
 
-Fieses zeugs: ein sixxs und ein 6to4. Kommt rein via sixxs, geht raus ueber
-6to4 wenn ping von einem anderen 6to4-rechner (route hat 2002::/16)! Ping geht,
-ssh aber nicht == boinks kann evnt. mit TOS markiert werden und mit einer
-policyroute aussortiert. Brrr.
+Note on ubuntu. One needs to enable prefer-family in /etc/wgetrc. after this
+e.g. "wget -O /dev/null http://ftp.se.debian.org" should connect to the IPv6
+addrs of that server. Alternative: change presedence of ULAs in /etc/gai.conf
 
 Idea to think about: --salt 3b5b91c5a2 XOR client addresses for some more
 privacy
 
 Motivation
 
-My internet access at home is realized by a wireless community mesh network not
+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
+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:
 
@@ -111,27 +212,27 @@ address translation (NAT). Using NAT has the following effects:
 
   ● Anonymization - nice to have as an option but not mission critical
 
-  ● ISP independance - no reverse routing, no "buy-a-number-range"
+  ● ISP independence - no reverse routing, no "buy-a-number-range"
 
-The last point _is_ mission critical. One can use a provider independant IPv6
+The last point _is_ mission critical. One can use 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 that
 address range to be re-routed to your new location.
 
-ISP independance is also possible with some tunneling technique, such as VPN or
+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 adresses (or
-"ULA") to transport the tunnel data between the client PC and the gateway/
+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.
 
 Using private IP addresses on the mesh nodes has a drawback: mesh node software
-updates e.g. via http downloads from an Internet server is not possible. This
+updates e.g. via HTTP downloads from an Internet server is not possible. This
 is where I start to think: "hey, some kind of address mapping may be nice to
-have". While opening pandoras NAT66 box, I discovered that IPv6 nerds do not
-like the acronym. It is always a good tactic in infowars to rename, hence the
+have". 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".
 
 // Sven-Ola