[PATCH] doc: add some examples for IPv6 NAT configuration
Add some expanded examples for the nat ipv6 introduced with
927acaedec7effbe67a154d8bfa0e67f7d08e6c7.
Unfortunately while for IPv4 it's well-known what addresses ranges are
useful for NAT, with IPv6 unless you enjoy digging through RFC's going
back-and-forth over unique local addresses and the meaning of the word
"site" it's generally much less obvious. I've tried to add some
details on choosing a range inline with RFC 4193 and then some
pointers for when it maybe doesn't work in the guest as you first
expect despite you doing what the RFC's say!
Signed-off-by: Ian Wienand <iwienand(a)redhat.com>
---
docs/formatnetwork.html.in | 47 ++++++++++++++++++++++++++++++++++++++
1 file changed, 47 insertions(+)
diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in
index fb740111b1..94a4cab4d1 100644
--- a/docs/formatnetwork.html.in
+++ b/docs/formatnetwork.html.in
@@ -1209,6 +1209,53 @@
</ip>
</network></pre>
+ <h3><a id="examplesNATv6">IPv6 NAT based
network</a></h3>
+
+ <p>
+ Below is a variation for also providing IPv6 NAT. This can be
+ especially useful when using multiple interfaces where some,
+ such as WiFi cards, can not be bridged (usually on a laptop),
+ making it difficult to provide end-to-end IPv6 routing.
+ </p>
+
+ <pre>
+<network>
+ <name>default6</name>
+ <bridge name="virbr0"/>
+ <forward mode="nat">
+ <nat ipv6='yes'>
+ <port start='1024' end='65535'/>
+ </nat>
+
+ <ip address="192.168.122.1" netmask="255.255.255.0">
+ <dhcp>
+ <range start="192.168.122.2"
end="192.168.122.254"/>
+ </dhcp>
+ </ip>
+ <ip family="ipv6" address="fdXX:XXXX:XXXX:NNNN::
prefix="64"/>
+ </ip>
+</network></pre>
+
+ <p>IPv6 NAT addressing has some caveats over the more straight
+ forward IPv4 case.
+ <a href="https://tools.ietf.org/html/rfc4193">RFC 4193</a>
+ defines the address range <tt>fd00::/8</tt> for <tt>/48</tt>
IPv6
+ private networks. It should be concatenated with a random 40-bit
+ string (i.e. 10 random hexadecimal digits replacing the <tt>X</tt>
+ values above, RFC 4193 provides
+ an <a
href="https://tools.ietf.org/html/rfc4193#section-3.2.2">alg...
+ if you do not have a source of sufficient randomness). This
+ leaves <tt>0</tt> through <tt>ffff</tt> for subnets
(<tt>N</tt>
+ above) which you can use at will.</p>
+
+ <p>Many operating systems will not consider these addresses as
+ preferential to IPv4, due to some practial history of these
+ addresses being present but unroutable and causing networking
+ issues. On many Linux distributions, you may need to
+ override <tt>/etc/gai.conf</tt> with values
+ from <a href="https://www.ietf.org/rfc/rfc3484.txt">RFC
3484</a>
+ to have your IPv6 NAT network correctly preferenced over IPv4.</p>
+
<h3><a id="examplesRoute">Routed network
config</a></h3>
<p>
--
2.26.2