diff --git a/server/client.go b/server/client.go
index 9f09283a..256a94cc 100644
--- a/server/client.go
+++ b/server/client.go
@@ -4521,6 +4521,8 @@ func (c *client) diagnosticsLoop() {
 			}
 			return
 		}
+		// Log before populate, so that the previous metrics are available.
+		(&c.diagTCPData).LogInteresting(c, routeID, &c.diagMetrics)
 		(&c.diagMetrics).PopulateFromTCPDiagnostics(&c.diagTCPData, expvarMaps, routeID)
 		c.mu.Unlock()
 	}
@@ -4555,3 +4557,8 @@ func (c *client) Warnf(format string, v ...interface{}) {
 	format = fmt.Sprintf("%s - %s", c, format)
 	c.srv.Warnf(format, v...)
 }
+
+func (c *client) Fatalf(format string, v ...interface{}) {
+	format = fmt.Sprintf("%s - %s", c, format)
+	c.srv.Fatalf(format, v...)
+}
diff --git a/server/tcpinfo_linux.go b/server/tcpinfo_linux.go
index e21ac9c4..557cc47f 100644
--- a/server/tcpinfo_linux.go
+++ b/server/tcpinfo_linux.go
@@ -170,3 +170,20 @@ func populateExpvarMapsTCPDiagnostics(maps *TCPInfoExpMaps, fullLabel string, me
 		vm.Field(i).Interface().(*expvar.Map).Set(fullLabel, vmetrics.FieldByName(tm.Field(i).Name))
 	}
 }
+
+func (d *TCPDiagnostics) LogInteresting(log Logger, fullLabel string, previous *TCPInfoExpMetrics) {
+	if int64(d.Info.Pmtu) != previous.PathMTU.Value() {
+		log.Noticef("[SOCKET-DIAGNOSTICS] %q: Path MTU change: was %v now %v",
+			fullLabel, previous.PathMTU.Value(), d.Info.Pmtu)
+	}
+	if int64(d.Info.Lost) != previous.LostPackets.Value() {
+		v := previous.LostPackets.Value()
+		log.Warnf("[SOCKET-DIAGNOSTICS] %q: LOST PACKETS: was %v now %v INCREASE: %v",
+			fullLabel, v, int64(d.Info.Lost), v-int64(d.Info.Lost))
+	}
+	if int64(d.Info.Total_retrans) != previous.TotalRetransPackets.Value() {
+		v := previous.TotalRetransPackets.Value()
+		log.Warnf("[SOCKET-DIAGNOSTICS] %q: total retransmission increase: was %v now %v INCREASE: %v",
+			fullLabel, v, int64(d.Info.Total_retrans), v-int64(d.Info.Total_retrans))
+	}
+}
diff --git a/server/tcpinfo_other.go b/server/tcpinfo_other.go
index 837bf563..e4ce706b 100644
--- a/server/tcpinfo_other.go
+++ b/server/tcpinfo_other.go
@@ -45,4 +45,6 @@ func NewTCPInfoExpMaps() *TCPInfoExpMaps {
 	return &TCPInfoExpMaps{}
 }
 
+func (d *TCPDiagnostics) LogInteresting(log Logger, fullLabel string, previous *TCPInfoExpMetrics) {}
+
 // There will be other functions here, as we populate maps.