doc: Document update-source <IFNAME> command better

There was a question in regards to how the update-source choose the ip address for the source when using the `update-source` command in BGP. Upon looking at the code, I was a but surprised, so I decided to document this behavior. Signed-off-by: Donald Sharp <[email protected]>
FRRouting · Feb 5, 2024 · 5842a70 · 5842a70
1 parent cac925f
commit 5842a70
Showing 1 changed file with 5 additions and 3 deletions.
diff --git a/doc/user/bgp.rst b/doc/user/bgp.rst
@@ -1626,10 +1626,12 @@ Configuring Peers
 
 .. clicmd:: neighbor PEER update-source <IFNAME|ADDRESS>
 
-   Specify the IPv4 source address to use for the :abbr:`BGP` session to this
-   neighbour, may be specified as either an IPv4 address directly or as an
+   Specify the IPv4 or IPv6 source address to use for the :abbr:`BGP` session to this
+   neighbour, may be specified as either an IP address directly or as an
    interface name (in which case the *zebra* daemon MUST be running in order
-   for *bgpd* to be able to retrieve interface state).
+   for *bgpd* to be able to retrieve interface state).  When there are multiple
+   addresses on the choosen IFNAME then BGP will use the address that matches
+   the most number of bits in comparison to the destination peer address.
 
    .. code-block:: frr