Babel: Send out low-interval hello on shutdown

When shutting down a Babel instance we send a wildcard retraction to make
sure all peers can quickly switch to other route origins. Add another small
optimisation borrowed from babeld: sending a Hello message (along with the
retraction) with a very low interval.

This will cause neighbours to modify their expiry timers for the node's
state to quickly time it out, thus conserving resources in the network.

1 files changed, 9 insertions, 4 deletions

diff --git a/proto/babel/babel.c b/proto/babel/babel.c
index 174fc9e2..4a7d550f 100644
--- a/proto/babel/babel.c
+++ b/proto/babel/babel.c
@@ -842,14 +842,14 @@ babel_send_ihus(struct babel_iface *ifa)
 }
 
 static void
-babel_send_hello(struct babel_iface *ifa)
+babel_send_hello(struct babel_iface *ifa, uint interval)
 {
   struct babel_proto *p = ifa->proto;
   union babel_msg msg = {};
 
   msg.type = BABEL_TLV_HELLO;
   msg.hello.seqno = ifa->hello_seqno++;
-  msg.hello.interval = ifa->cf->hello_interval;
+  msg.hello.interval = interval ?: ifa->cf->hello_interval;
 
   TRACE(D_PACKETS, "Sending hello on %s with seqno %d interval %t",
 	ifa->ifname, msg.hello.seqno, (btime) msg.hello.interval);
@@ -1557,7 +1557,7 @@ babel_iface_timer(timer *t)
 
   if (now_ >= ifa->next_hello)
   {
-    babel_send_hello(ifa);
+    babel_send_hello(ifa, 0);
     ifa->next_hello += hello_period * (1 + (now_ - ifa->next_hello) / hello_period);
   }
 
@@ -1604,7 +1604,7 @@ babel_iface_start(struct babel_iface *ifa)
   tm_start(ifa->timer, 100 MS);
   ifa->up = 1;
 
-  babel_send_hello(ifa);
+  babel_send_hello(ifa, 0);
   babel_send_wildcard_retraction(ifa);
   babel_send_wildcard_request(ifa);
   babel_send_update(ifa, 0);	/* Full update */
@@ -2417,6 +2417,11 @@ babel_iface_shutdown(struct babel_iface *ifa)
 {
   if (ifa->sk)
   {
+    /*
+     * Retract all our routes and lower the hello interval so peers' neighbour
+     * state expires quickly
+     */
+    babel_send_hello(ifa, BABEL_MIN_INTERVAL);
     babel_send_wildcard_retraction(ifa);
     babel_send_queue(ifa);
   }