doc: iopv6 precedence

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

1 files changed, 44 insertions, 5 deletions

diff --git a/README.dbk b/README.dbk
index 7fc6aff..3e8ff18 100644
--- a/README.dbk
+++ b/README.dbk
@@ -175,13 +175,52 @@ ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-
   </section>
 
   <section>
-    <title>Hints (Chapter is To-do)</title>
+    <title>IPv6/IPv4 Precedence</title>
 
-    <para>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</para>
+    <para>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 <filename>/etc/gai.conf</filename> file will
+    give you a hint on this.</para>
 
-    <para>Idea to think about: --salt 3b5b91c5a2 XOR client addresses for some more privacy</para>
+    <para>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 <filename>/etc/gai.conf</filename>.</para>
+
+    <note>
+      <para>The getaddrinfo() library function manages lists of label, precedence, and scope4 type entries. If the
+      <filename>/etc/gai.conf</filename> 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 <quote>label</quote> lines compare source addresses, the precedence lines compare
+      <quote>destination</quote> addresses.</para>
+    </note>
+
+    <procedure>
+      <title>Change IPv6 Precedence</title>
+
+      <step>
+        <para>Open the <filename>/etc/gai.conf</filename> file as root user, e.g. by executing <userinput>sudo nano
+        /etc/gai.conf</userinput>.</para>
+      </step>
+
+      <step>
+        <para>Remove the leading hash character from the 8 lines starting with <quote>#label</quote>.</para>
+      </step>
+
+      <step>
+        <para>Re-add the hash character to the line stating <quote>#label fc00::/7 6</quote>.</para>
+      </step>
+
+      <step>
+        <para>Save the file.</para>
+      </step>
+
+      <step>
+        <para>Restart your browser and re-try to browse to a multi-homed web site.</para>
+      </step>
+    </procedure>
+
+    <para>The above procedure removes the difference between standard IPv6 source addresses and ULA type private IPv6 source
+    addresses. Anything else is unchanged.</para>
   </section>
 
   <section id="motivation">