doc: iopv6 precedence

git-svn-id: https://map66.svn.sourceforge.net/svnroot/map66@8 3484d885-4da6-438d-b19d-107d078dd756

1 files changed, 37 insertions, 7 deletions

diff --git a/README.txt b/README.txt
index 2e2eaf0..57abc4a 100644
--- a/README.txt
+++ b/README.txt
@@ -17,7 +17,7 @@ Configuration
     Brief Version
     Detailed Version
 
-Hints (Chapter is To-do)
+IPv6/IPv4 Precedence
 Motivation
 
 These files implement a Linux netfilter target that changes the IPv6 address of
@@ -186,14 +186,44 @@ 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...
 
-Hints (Chapter is To-do)
+IPv6/IPv4 Precedence
 
-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
+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 /etc/gai.conf file will give you a hint on this.
 
-Idea to think about: --salt 3b5b91c5a2 XOR client addresses for some more
-privacy
+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 /etc/gai.conf.
+
+Note
+
+The getaddrinfo() library function manages lists of label, precedence, and
+scope4 type entries. If the /etc/gai.conf 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 “label” lines compare source
+addresses, the 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 fc00::/7 6”.
+
+ 4. Save the file.
+
+ 5. Restart your browser and re-try to browse to a multi-homed web site.
+
+The above procedure removes the difference between standard IPv6 source
+addresses and ULA type private IPv6 source addresses. Anything else is
+unchanged.
 
 Motivation