BGP: Add option to enforce first AS in AS_PATH

[thirdparty/bird.git] / doc / bird.sgml

diff --git a/doc/bird.sgml b/doc/bird.sgml
index d2a4fc143b2fc12a8b1ffbfe3a44c7087e7c2ac1..aeea613fd4107a30eee51dcb26c38e4d111741d0 100644 (file)
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -2405,6 +2405,15 @@ using the following configuration parameters:
        malformed and corresponding BGP updates are treated as withdraws.
        Default: on.
 
+       <tag><label id="bgp-enforce-first-as">enforce first as [<m/switch/]</tag>
+       Routes received from an EBGP neighbor are generally expected to have the
+       first (leftmost) AS number in their AS path equal to the neighbor AS
+       number. This is not enforced by default as there are legitimate cases
+       where it is not true, e.g. connections to route servers. When this
+       option is enabled, routes with non-matching first AS number are rejected
+       and corresponding updates are treated as withdraws. The option is valid
+       on EBGP sessions only. Default: off.
+
        <tag><label id="bgp-enable-route-refresh">enable route refresh <m/switch/</tag>
        After the initial route exchange, BGP protocol uses incremental updates
        to keep BGP speakers synchronized. Sometimes (e.g., if BGP speaker