From: Marco d'Itri <md@linux.it>
Date: Thu, 1 Jun 2017 16:18:34 +0200
Subject: [PATCH] adaptive_echos

---
 pppd/lcp.c  | 19 +++++++++++++++++++
 pppd/pppd.8 |  5 +++++
 2 files changed, 24 insertions(+)

diff --git a/pppd/lcp.c b/pppd/lcp.c
index 8ed2778bfb67..c97a64b7774f 100644
--- a/pppd/lcp.c
+++ b/pppd/lcp.c
@@ -73,6 +73,7 @@ static void lcp_delayed_up __P((void *));
  */
 int	lcp_echo_interval = 0; 	/* Interval between LCP echo-requests */
 int	lcp_echo_fails = 0;	/* Tolerance to unanswered echo-requests */
+bool	lcp_echo_adaptive = 0;	/* request echo only if the link was idle */
 bool	lax_recv = 0;		/* accept control chars in asyncmap */
 bool	noendpoint = 0;		/* don't send/accept endpoint discriminator */
 
@@ -151,6 +152,8 @@ static option_t lcp_option_list[] = {
       OPT_PRIO },
     { "lcp-echo-interval", o_int, &lcp_echo_interval,
       "Set time in seconds between LCP echo requests", OPT_PRIO },
+    { "lcp-echo-adaptive", o_bool, &lcp_echo_adaptive,
+      "Suppress LCP echo requests if traffic was received", 1 },
     { "lcp-restart", o_int, &lcp_fsm[0].timeouttime,
       "Set time in seconds between LCP retransmissions", OPT_PRIO },
     { "lcp-max-terminate", o_int, &lcp_fsm[0].maxtermtransmits,
@@ -2332,6 +2335,22 @@ LcpSendEchoRequest (f)
     }
 
     /*
+     * If adaptive echos have been enabled, only send the echo request if
+     * no traffic was received since the last one.
+     */
+    if (lcp_echo_adaptive) {
+	static unsigned int last_pkts_in = 0;
+
+	update_link_stats(f->unit);
+	link_stats_valid = 0;
+
+	if (link_stats.pkts_in != last_pkts_in) {
+	    last_pkts_in = link_stats.pkts_in;
+	    return;
+	}
+    }
+
+    /*
      * Make and send the echo request frame.
      */
     if (f->state == OPENED) {
diff --git a/pppd/pppd.8 b/pppd/pppd.8
index e2768b135273..b7fd0bdaab52 100644
--- a/pppd/pppd.8
+++ b/pppd/pppd.8
@@ -558,6 +558,11 @@ to 1) if the \fIproxyarp\fR option is used, and will enable the
 dynamic IP address option (i.e. set /proc/sys/net/ipv4/ip_dynaddr to
 1) in demand mode if the local address changes.
 .TP
+.B lcp\-echo\-adaptive
+If this option is used with the \fIlcp\-echo\-failure\fR option then
+pppd will send LCP echo\-request frames only if no traffic was received
+from the peer since the last echo\-request was sent.
+.TP
 .B lcp\-echo\-failure \fIn
 If this option is given, pppd will presume the peer to be dead
 if \fIn\fR LCP echo\-requests are sent without receiving a valid LCP