Doc: Documentation for BGP extended next hop feature

Thanks to Arvin Gan for the bugreport.

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 78569d28033f2a0ec0b61b36781452f7a0d398de..fde47e65b0aae1ac3aae4449bab823fce2198771 100644 (file)
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -2562,6 +2562,15 @@ be used in explicit configuration.
        explicitly (to conserve memory). This option requires that the connected
        routing table is <ref id="dsc-table-sorted" name="sorted">. Default: off.
 
+       <tag><label id="bgp-extended-next-hop">extended next hop <m/switch/</tag>
+       BGP expects that announced next hops have the same address family as
+       associated network prefixes. This option provides an extension to use
+       IPv4 next hops with IPv6 prefixes and vice versa. For IPv4 / VPNv4
+       channels, the behavior is controlled by the Extended Next Hop Encoding
+       capability, as described in <rfc id="5549">. For IPv6 / VPNv6 channels,
+       just IPv4-mapped IPv6 addresses are used, as described in
+       <rfc id="4798"> and <rfc id="4659">. Default: off.
+
        <tag><label id="bgp-add-paths">add paths <m/switch/|rx|tx</tag>
        Standard BGP can propagate only one path (route) per destination network
        (usually the selected one). This option controls the add-path protocol