doc: add "enforce-first-as" to BGP doc

With the deprecation of the global "bgp enforce-first-as" command back
in https://github.com/FRRouting/frr/pull/2259 the newly introduced
option to enable that setting on a specific peer was not documented.

This commit adds the necessary documentation and states the command's
default.

Signed-off-by: Manuel Schweizer <manuel.schweizer@cloudscale.ch>
(cherry picked from commit 3acc6ae932caf0e3c1eca3e2369230d300721a8b)

diff --git a/doc/user/bgp.rst b/doc/user/bgp.rst
index 7a7f9863bb3a0270ae7c72b5a7400bf27cc78ca1..5b8ec11320f59a4702524a3af10d4c45b6e6f13a 100644 (file)
--- a/doc/user/bgp.rst
+++ b/doc/user/bgp.rst
@@ -1504,6 +1504,13 @@ Configuring Peers
    value is carried encoded as uint32. To enable backward compatibility we
    need to disable IEEE floating-point encoding option per-peer.
 
+.. clicmd:: neighbor PEER enforce-first-as
+
+   Discard updates received from the specified (eBGP) peer if the AS_PATH
+   attribute does not contain the PEER's ASN as the first AS_PATH segment.
+
+   Default: disabled.
+
 .. clicmd:: neighbor PEER extended-optional-parameters
 
    Force Extended Optional Parameters Length format to be used for OPEN messages.