BGP: Improve handling of hold and keepalive timers

The effective keepalive time now scales relative to the negotiated
hold time, to maintain proportion between the keepalive time and the
hold time. This avoids issues when both keepalive and hold times
were configured, the hold time was negotiated to a smaller value,
but the keepalive time stayed the same.

Add new options 'min hold time' and 'min keepalive time', which reject
session attempts with too small hold time.

Improve validation of config options an their documentation.

Thanks to Alexander Zubkov and Sergei Goriunov for suggestions.

1 files changed, 17 insertions, 3 deletions

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 47848f82..8925c2cc 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -2750,9 +2750,16 @@ using the following configuration parameters:
 
 	<tag><label id="bgp-hold-time">hold time <m/number/</tag>
 	Time in seconds to wait for a Keepalive message from the other side
-	before considering the connection stale. Default: depends on agreement
-	with the neighboring router, we prefer 240 seconds if the other side is
-	willing to accept it.
+	before considering the connection stale. The effective value is
+	negotiated during session establishment and it is a minimum of this
+	configured value and the value proposed by the peer. The zero value has
+	a special meaning, signifying that no keepalives are used. Default: 240
+	seconds.
+
+	<tag><label id="bgp-min-hold-time">min hold time <m/number/</tag>
+	Minimum value of the hold time that is accepted during session negotiation.
+	If the peer proposes a lower value, the session is rejected with error.
+	Default: none.
 
 	<tag><label id="bgp-startup-hold-time">startup hold time <m/number/</tag>
 	Value of the hold timer used before the routers have a chance to exchange
@@ -2760,8 +2767,15 @@ using the following configuration parameters:
 
 	<tag><label id="bgp-keepalive-time">keepalive time <m/number/</tag>
 	Delay in seconds between sending of two consecutive Keepalive messages.
+	The effective value depends on the negotiated hold time, as it is scaled
+	to maintain proportion between the keepalive time and the hold time.
 	Default: One third of the hold time.
 
+	<tag><label id="bgp-min-keepalive-time">min keepalive time <m/number/</tag>
+	Minimum value of the keepalive time that is accepted during session
+	negotiation. If the proposed hold time would lead to a lower value of
+	the keepalive time, the session is rejected with error. Default: none.
+
 	<tag><label id="bgp-connect-delay-time">connect delay time <m/number/</tag>
 	Delay in seconds between protocol startup and the first attempt to
 	connect. Default: 5 seconds.