diff --git a/server/src/if.c b/server/src/if.c
index 368b2eeed..0027e8bd7 100644
--- a/server/src/if.c
+++ b/server/src/if.c
@@ -58,22 +58,30 @@ int if_start(struct interface *i, int affinity)
 		info("Starting interface '%s' (index=%u)", i->name, i->index);
 	
 	{ INDENT
+		/* Assign fwmark's to socket nodes which have netem options */
 		int mark = 0;
 		FOREACH(&i->sockets, it) {
 			struct socket *s = it->socket;
-
-			if (s->netem) {
+			if (s->netem)
 				s->mark = 1 + mark++;
+		}
 		
+		/* Abort if no node is using netem */
+		if (mark == 0)
+			return 0;
+
+		/* Replace root qdisc */
+		tc_prio(i, TC_HDL(4000, 0), mark);
+		
+		/* Create netem qdisks and appropriate filter per netem node */
+		FOREACH(&i->sockets, it) {
+			struct socket *s = it->socket;
+			if (s->netem) {
 				tc_mark(i,  TC_HDL(4000, s->mark), s->mark);
 				tc_netem(i, TC_HDL(4000, s->mark), s->netem);
 			}
 		}
 
-		/* Create priority qdisc */
-		if (mark)
-			tc_prio(i, TC_HDL(4000, 0), mark);
-
 		/* Set affinity for network interfaces (skip _loopback_ dev) */
 		if_getirqs(i);
 		if_setaffinity(i, affinity);
diff --git a/server/src/tc.c b/server/src/tc.c
index be29ad1bb..00d62a870 100644
--- a/server/src/tc.c
+++ b/server/src/tc.c
@@ -45,7 +45,10 @@ int tc_reset(struct interface *i)
 
 	debug(6, "Reset traffic control for interface '%s'", i->name);
 
-	return system2(cmd);
+	if (system2(cmd))
+		error("Failed to add reset traffic control for interface '%s'", i->name);
+	
+	return 0;
 }
 
 int tc_prio(struct interface *i, tc_hdl_t handle, int bands)
@@ -55,7 +58,7 @@ int tc_prio(struct interface *i, tc_hdl_t handle, int bands)
 	int priomap[] = { 1, 2, 2, 2, 1, 2, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1 };
 
 	len += snprintf(cmd+len, sizeof(cmd)-len,
-		"tc qdisc add dev %s root handle %u prio bands %u priomap",
+		"tc qdisc replace dev %s root handle %u prio bands %u priomap",
 		i->name, TC_HDL_MAJ(handle), bands + 3);
 
 	for (int i = 0; i < 16; i++)
@@ -63,7 +66,10 @@ int tc_prio(struct interface *i, tc_hdl_t handle, int bands)
 
 	debug(6, "Replace master qdisc for interface '%s'", i->name);
 
-	return system2(cmd);
+	if (system2(cmd))
+		error("Failed to add prio qdisc for interface '%s'", i->name);
+	
+	return 0;
 }
 
 int tc_netem(struct interface *i, tc_hdl_t parent, struct netem *em)
@@ -71,7 +77,7 @@ int tc_netem(struct interface *i, tc_hdl_t parent, struct netem *em)
 	int len = 0;
 	char cmd[256];
 	len += snprintf(cmd+len, sizeof(cmd)-len,
-		"tc qdisc add dev %s parent %u:%u netem",
+		"tc qdisc replace dev %s parent %u:%u netem",
 		i->name, TC_HDL_MAJ(parent), TC_HDL_MIN(parent));
 
 	if (em->valid & TC_NETEM_DELAY) {
@@ -92,19 +98,24 @@ int tc_netem(struct interface *i, tc_hdl_t parent, struct netem *em)
 
 	debug(6, "Setup netem qdisc for interface '%s'", i->name);
 
-	return system2(cmd);
+	if (system2(cmd))
+		error("Failed to add netem qdisc for interface '%s'", i->name);
+
+	return 0;
 }
 
 int tc_mark(struct interface *i, tc_hdl_t flowid, int mark)
 {
 	char cmd[128];
 	snprintf(cmd, sizeof(cmd),
-		"tc filter add dev %s protocol ip handle %u fw flowid %u:%u",
+		"tc filter replace dev %s protocol ip handle %u fw flowid %u:%u",
 		i->name, mark, TC_HDL_MAJ(flowid), TC_HDL_MIN(flowid));
 
 	debug(7, "Add traffic filter to interface '%s': fwmark %u => flowid %u:%u",
 		i->name, mark, TC_HDL_MAJ(flowid), TC_HDL_MIN(flowid));
 
-	return system2(cmd);
+	if (system2(cmd))
+		error("Failed to add fw_mark classifier for interface '%s'", i->name);
 
+	return 0;
 }