diff --git a/include/csp/csp_iflist.h b/include/csp/csp_iflist.h
index 07194a07d..478805545 100644
--- a/include/csp/csp_iflist.h
+++ b/include/csp/csp_iflist.h
@@ -25,6 +25,14 @@ void csp_iflist_add(csp_iface_t * iface);
  */
 void csp_iflist_remove(csp_iface_t * ifc);
 
+/**
+ * Iterate over the list of interfaces.
+ *
+ * @param[in] ifc Previous interface to continue iteration, or NULL to start at the head of the list.
+ * @return Pointer to the next interface, or NULL if the end of the list is reached.
+ */
+csp_iface_t * csp_iflist_iterate(csp_iface_t * ifc);
+
 csp_iface_t * csp_iflist_get_by_name(const char * name);
 csp_iface_t * csp_iflist_get_by_addr(uint16_t addr);
 csp_iface_t * csp_iflist_get_by_broadcast(uint16_t addr);
diff --git a/include/csp/interfaces/csp_if_zmqhub.h b/include/csp/interfaces/csp_if_zmqhub.h
index a26ac29d4..ae6cec903 100644
--- a/include/csp/interfaces/csp_if_zmqhub.h
+++ b/include/csp/interfaces/csp_if_zmqhub.h
@@ -130,14 +130,14 @@ void * csp_zmqhub_fixup_cspv1_del_dest_addr(uint8_t * rx_data, size_t * datalen)
  *
  * Safe to call after `csp_zmqhub_init_filter2()` to change promiscuity.
  */
-void csp_zmqhub_remove_filters(csp_iface_t * zmq_iface);
+int csp_zmqhub_remove_filters(csp_iface_t * zmq_iface);
 
 /**
  * Make `zmq_iface` unpromiscuous, only parse matching unicast and broadcast addresses.
  *
  * Safe to call after `csp_zmqhub_init_filter2()` to change promiscuity.
  */
-void csp_zmqhub_add_filters(csp_iface_t * zmq_iface);
+int csp_zmqhub_add_filters(csp_iface_t * zmq_iface);
 
 
 #ifdef __cplusplus
diff --git a/src/csp_iflist.c b/src/csp_iflist.c
index 7febfffab..2d121b367 100644
--- a/src/csp_iflist.c
+++ b/src/csp_iflist.c
@@ -19,7 +19,7 @@ int csp_iflist_is_within_subnet(uint16_t addr, csp_iface_t * ifc) {
 	if (ifc == NULL) {
 		return 0;
 	}
-	
+
 	uint16_t netmask = ((1 << ifc->netmask) - 1) << (csp_id_get_host_bits() - ifc->netmask);
 	uint16_t network_a = ifc->addr & netmask;
 	uint16_t network_b = addr & netmask;
@@ -87,7 +87,7 @@ csp_iface_t * csp_iflist_get_by_isdfl(csp_iface_t * ifc) {
 
 }
 
-static csp_iface_t * csp_iflist_iterate(csp_iface_t * ifc) {
+csp_iface_t * csp_iflist_iterate(csp_iface_t * ifc) {
 
 	/* Head of list */
 	if (ifc == NULL) {
diff --git a/src/interfaces/csp_if_zmqhub.c b/src/interfaces/csp_if_zmqhub.c
index 20ff18c70..b726decae 100644
--- a/src/interfaces/csp_if_zmqhub.c
+++ b/src/interfaces/csp_if_zmqhub.c
@@ -269,7 +269,11 @@ int csp_zmqhub_init_w_name_endpoints_rxfilter(const char * ifname, uint16_t addr
 	return CSP_ERR_NONE;
 }
 
-void csp_zmqhub_remove_filters(csp_iface_t * zmq_iface) {
+int csp_zmqhub_remove_filters(csp_iface_t * zmq_iface) {
+
+	if(zmq_iface == NULL || zmq_iface->driver_data == NULL || zmq_iface->nexthop != csp_zmqhub_tx) {
+		return -1;
+	}
 
 	int ret = 0;
 	zmq_driver_t * drv = zmq_iface->driver_data;
@@ -290,7 +294,7 @@ void csp_zmqhub_remove_filters(csp_iface_t * zmq_iface) {
 	/* subscribe to all packets - no filter */
 	ret = zmq_setsockopt(drv->subscriber, ZMQ_SUBSCRIBE, NULL, 0);
 	assert(ret == 0);
-	(void)ret;
+	return ret;
 }
 
 static int csp_zmqhub_add_filter(void * driver_data, uint16_t addr) {
@@ -307,8 +311,11 @@ static int csp_zmqhub_add_filter(void * driver_data, uint16_t addr) {
 	return ret;
 }
 
-void csp_zmqhub_add_filters(csp_iface_t * zmq_iface) {
+int csp_zmqhub_add_filters(csp_iface_t * zmq_iface) {
 
+	if(zmq_iface == NULL || zmq_iface->driver_data == NULL || zmq_iface->nexthop != csp_zmqhub_tx) {
+		return -1;
+	}
 	int ret = 0;
 	zmq_driver_t * drv = zmq_iface->driver_data;
 	const uint16_t addr = zmq_iface->addr;
@@ -329,11 +336,11 @@ void csp_zmqhub_add_filters(csp_iface_t * zmq_iface) {
 		ret = zmq_setsockopt(drv->subscriber, ZMQ_SUBSCRIBE, &drv->filt[i][2], 2);
 	}
 	assert(ret == 0);
-	(void)ret;
+	return ret;
 }
 
 int csp_zmqhub_init_filter2(const char * ifname, const char * host, uint16_t addr, uint16_t netmask, int promisc, csp_iface_t ** return_interface, char * sec_key, uint16_t subport, uint16_t pubport) {
-	
+
 	/* ZMQ will cause valgrind errors if `sec_key` isn't exactly 40 characters long.
 		For now we deliberately parse an empty string as if no sec_key was specified. */
 	const ssize_t sec_key_len = sec_key ? strnlen(sec_key, CURVE_KEYLEN-1) : 0;
@@ -411,7 +418,7 @@ int csp_zmqhub_init_filter2(const char * ifname, const char * host, uint16_t add
 	zmq_setsockopt(drv->subscriber, ZMQ_TCP_KEEPALIVE_IDLE, &idle, sizeof(idle));
 	zmq_setsockopt(drv->subscriber, ZMQ_TCP_KEEPALIVE_CNT, &cnt, sizeof(cnt));
 	zmq_setsockopt(drv->subscriber, ZMQ_TCP_KEEPALIVE_INTVL, &intvl, sizeof(intvl));
-	
+
 	/* Connect to server */
 	ret = zmq_connect(drv->publisher, pub);
 	assert(ret == 0);