diff --git a/include/node.h b/include/node.h
index 686b54044..b5a15df33 100644
--- a/include/node.h
+++ b/include/node.h
@@ -171,15 +171,8 @@ struct node
 		NODE_STOPPED	/**< Node was running, but has been stopped by calling node_close() */
 	} state;		/**< Node state */
 
-	struct node_type *_vt;	/**< C++ like virtual function call table */
-
-	union {
-		struct socket *socket;
-		struct opal   *opal;
-		struct gtfpga *gtfpga;
-		struct file   *file;
-		struct ngsi   *ngsi;
-	};	/** Virtual data (used by struct node::_vt functions) */
+	struct node_type *_vt;	/**< Virtual functions (C++ OOP style) */
+	void *_vd;		/**< Virtual data (used by struct node::_vt functions) */
 
 	config_setting_t *cfg;	/**< A pointer to the libconfig object which instantiated this node */
 };
diff --git a/lib/file.c b/lib/file.c
index eb00a2814..37401e14b 100644
--- a/lib/file.c
+++ b/lib/file.c
@@ -18,7 +18,7 @@
 
 int file_reverse(struct node *n)
 {
-	struct file *f = n->file;
+	struct file *f = n->_vd;
 
 	SWAP(f->read, f->write);
 
@@ -70,7 +70,7 @@ static int file_parse_direction(config_setting_t *cfg, struct file *f, int d)
 
 int file_parse(struct node *n, config_setting_t *cfg)
 {
-	struct file *f = alloc(sizeof(struct file));
+	struct file *f = n->_vd;
 	
 	config_setting_t *cfg_in, *cfg_out;
 	
@@ -117,14 +117,14 @@ int file_parse(struct node *n, config_setting_t *cfg)
 			cerror(cfg_in, "Invalid value '%s' for setting 'epoch_mode'", epoch_mode);
 	}
 
-	n->file = f;
+	n->_vd = f;
 
 	return 0;
 }
 
 char * file_print(struct node *n)
 {
-	struct file *f = n->file;
+	struct file *f = n->_vd;
 	char *buf = NULL;
 	
 	if (f->read.fmt) {
@@ -178,7 +178,7 @@ char * file_print(struct node *n)
 
 int file_open(struct node *n)
 {
-	struct file *f = n->file;
+	struct file *f = n->_vd;
 	
 	struct timespec now = time_now();
 
@@ -258,7 +258,7 @@ int file_open(struct node *n)
 
 int file_close(struct node *n)
 {
-	struct file *f = n->file;
+	struct file *f = n->_vd;
 	
 	free(f->read.path);
 	free(f->write.path);
@@ -275,8 +275,8 @@ int file_close(struct node *n)
 
 int file_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
+	struct file *f = n->_vd;
 	int values, flags, i = 0;
-	struct file *f = n->file;
 
 	if (f->read.handle) {
 		for (i = 0; i < cnt; i++) {
@@ -338,7 +338,7 @@ retry:			values = msg_fscan(f->read.handle, cur, &flags, NULL);
 int file_write(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
 	int i = 0;
-	struct file *f = n->file;
+	struct file *f = n->_vd;
 
 	if (f->write.handle) {
 		for (i = 0; i < cnt; i++) {
@@ -364,6 +364,7 @@ int file_write(struct node *n, struct msg *pool, int poolsize, int first, int cn
 static struct node_type vt = {
 	.name		= "file",
 	.description	= "support for file log / replay node type",
+	.size		= sizeof(struct file),
 	.reverse	= file_reverse,
 	.parse		= file_parse,
 	.print		= file_print,
diff --git a/lib/gtfpga.c b/lib/gtfpga.c
index c362a1ebd..6df6bab48 100644
--- a/lib/gtfpga.c
+++ b/lib/gtfpga.c
@@ -58,7 +58,7 @@ int gtfpga_deinit()
 
 int gtfpga_parse(struct node *n, config_setting_t *cfg)
 {
-	struct gtfpga *g = alloc(sizeof(struct gtfpga));
+	struct gtfpga *g = n->_vd;
 
 	const char *slot, *id, *err;
 	config_setting_t *cfg_slot, *cfg_id;
@@ -92,14 +92,12 @@ int gtfpga_parse(struct node *n, config_setting_t *cfg)
 	if (!config_setting_lookup_float(cfg, "rate", &g->rate))
 		g->rate = 0;
 
-	n->gtfpga = g;
-
 	return 0;
 }
 
 char * gtfpga_print(struct node *n)
 {
-	struct gtfpga *g = n->gtfpga;
+	struct gtfpga *g = n->_vd;
 	char *buf = NULL;
 
 	if (g->dev) {
@@ -181,7 +179,7 @@ static int gtfpga_mmap(struct gtfpga *g)
 
 int gtfpga_open(struct node *n)
 {
-	struct gtfpga *g = n->gtfpga;
+	struct gtfpga *g = n->_vd;
 	struct pci_dev *dev;
 
 	int ret;
@@ -223,7 +221,7 @@ int gtfpga_open(struct node *n)
 
 int gtfpga_close(struct node *n)
 {
-	struct gtfpga *g = n->gtfpga;
+	struct gtfpga *g = n->_vd;
 
 	if (g->map)
 		munmap(g->map, g->dev->size[GTFPGA_BAR]);
@@ -238,7 +236,7 @@ int gtfpga_close(struct node *n)
 /** @todo implement */
 int gtfpga_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct gtfpga *g = n->gtfpga;
+	struct gtfpga *g = n->_vd;
 
 	struct msg *m = &pool[first % poolsize];
 	
@@ -258,7 +256,7 @@ int gtfpga_read(struct node *n, struct msg *pool, int poolsize, int first, int c
 /** @todo implement */
 int gtfpga_write(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	// struct gtfpga *g = n->gtfpga;
+	// struct gtfpga *g = n->_vd;
 	// struct msg *m = &pool[first % poolsize];
 	
 	if (cnt != 1)
diff --git a/lib/ngsi.c b/lib/ngsi.c
index b1f22bbca..3eba383ea 100644
--- a/lib/ngsi.c
+++ b/lib/ngsi.c
@@ -430,7 +430,7 @@ int ngsi_deinit()
 
 int ngsi_parse(struct node *n, config_setting_t *cfg)
 {
-	struct ngsi *i = alloc(sizeof(struct ngsi));
+	struct ngsi *i = n->_vd;
 
 	if (!config_setting_lookup_string(cfg, "access_token", &i->access_token))
 		i->access_token = NULL; /* disabled by default */
@@ -458,8 +458,6 @@ int ngsi_parse(struct node *n, config_setting_t *cfg)
 		cerror(cfg, "Missing mapping for node %s", node_name(n));
 
 	if (ngsi_parse_mapping(&i->mapping, cfg_mapping))
-
-	n->ngsi = i;
 		cerror(cfg_mapping, "Invalid mapping for node %s", node_name(n));
 	
 	return 0;
@@ -467,7 +465,7 @@ int ngsi_parse(struct node *n, config_setting_t *cfg)
 
 char * ngsi_print(struct node *n)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	char *buf = NULL;
 
 	return strcatf(&buf, "endpoint=%s, timeout=%.3f secs, #mappings=%zu",
@@ -476,7 +474,7 @@ char * ngsi_print(struct node *n)
 
 int ngsi_destroy(struct node *n)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	
 	list_destroy(&i->mapping);
 	
@@ -485,7 +483,7 @@ int ngsi_destroy(struct node *n)
 
 int ngsi_open(struct node *n)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	int ret;
 	
 	i->curl = curl_easy_init();
@@ -537,7 +535,7 @@ int ngsi_open(struct node *n)
 
 int ngsi_close(struct node *n)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	int ret;
 	
 	/* Delete complete entity (not just attributes) */
@@ -555,7 +553,7 @@ int ngsi_close(struct node *n)
 
 int ngsi_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	int ret;
 	
 	timerfd_wait(i->tfd);
@@ -579,7 +577,7 @@ out:	json_decref(entity);
 
 int ngsi_write(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct ngsi *i = n->ngsi;
+	struct ngsi *i = n->_vd;
 	int ret;
 	
 	json_t *entity = ngsi_build_entity(i, pool, poolsize, first, cnt, NGSI_ENTITY_VALUES);
@@ -594,6 +592,7 @@ int ngsi_write(struct node *n, struct msg *pool, int poolsize, int first, int cn
 static struct node_type vt = {
 	.name		= "ngsi",
 	.description	= "OMA Next Generation Services Interface 10 (libcurl, libjansson, libuuid)",
+	.size		= sizeof(struct ngsi),
 	.parse		= ngsi_parse,
 	.print		= ngsi_print,
 	.open		= ngsi_open,
diff --git a/lib/node.c b/lib/node.c
index 5120c4ab8..d11c80062 100644
--- a/lib/node.c
+++ b/lib/node.c
@@ -130,6 +130,11 @@ struct node * node_create(struct node_type *vt)
 	list_push(&vt->instances, n);
 	
 	n->_vt = vt;
+	n->_vd = alloc(n->_vt->size);
+	
+	if (n->_vt->create)
+		n->_vt->create(n);
+
 	n->state = NODE_CREATED;
 	
 	return n;
@@ -140,7 +145,7 @@ void node_destroy(struct node *n)
 	if (n->_vt->destroy)
 		n->_vt->destroy(n);
 
-	free(n->socket);
+	free(n->_vd);
 	free(n->_name);
 	free(n);
 }
diff --git a/lib/opal.c b/lib/opal.c
index 01378cfa2..59af0ba5b 100644
--- a/lib/opal.c
+++ b/lib/opal.c
@@ -130,15 +130,12 @@ int opal_print_global(struct opal_global *g)
 
 int opal_parse(struct node *n, config_setting_t *cfg)
 {
-	struct opal *o = alloc(sizeof(struct opal));
+	struct opal *o = n->_vd;
 
 	config_setting_lookup_int(cfg, "send_id", &o->send_id);
 	config_setting_lookup_int(cfg, "recv_id", &o->recv_id);
 	config_setting_lookup_bool(cfg, "reply", &o->reply);
 
-	n->opal = o;
-	n->cfg = cfg;
-
 	return 0;
 }
 
@@ -155,7 +152,7 @@ char * opal_print(struct node *n)
 
 int opal_open(struct node *n)
 {
-	struct opal *o = n->opal;
+	struct opal *o = n->_vd;
 
 	if (!og)
 		error("The server was not started as an OPAL asynchronous process!");
@@ -187,7 +184,7 @@ int opal_close(struct node *n)
 
 int opal_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct opal *o = n->opal;
+	struct opal *o = n->_vd;
 
 	int state, len, ret;
 	unsigned id;
@@ -252,7 +249,7 @@ int opal_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt
 
 int opal_write(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct opal *o = n->opal;
+	struct opal *o = n->_vd;
 
 	struct msg *m = &pool[first % poolsize];
 
@@ -286,6 +283,7 @@ int opal_write(struct node *n, struct msg *pool, int poolsize, int first, int cn
 static struct node_type vt = {
 	.name		= "opal",
 	.description	= "run as OPAL Asynchronous Process (libOpalAsyncApi)",
+	.size		= sizeof(struct opal),
 	.parse		= opal_parse,
 	.print		= opal_print,
 	.open		= opal_open,
diff --git a/lib/socket.c b/lib/socket.c
index 65afc106b..6fd332e35 100644
--- a/lib/socket.c
+++ b/lib/socket.c
@@ -48,7 +48,7 @@ int socket_init(int argc, char * argv[], struct settings *set)
 
 	/* Gather list of used network interfaces */
 	list_foreach(struct node *n, &vt.instances) {
-		struct socket *s = n->socket;
+		struct socket *s = n->_vd;
 		struct rtnl_link *link;
 
 		/* Determine outgoing interface */
@@ -85,7 +85,7 @@ int socket_deinit()
 
 char * socket_print(struct node *n)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 	char *layer = NULL, *buf = NULL;
 	
 	switch (s->layer) {
@@ -107,7 +107,7 @@ char * socket_print(struct node *n)
 
 int socket_open(struct node *n)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 	struct sockaddr_in *sin = (struct sockaddr_in *) &s->local;
 	struct sockaddr_ll *sll = (struct sockaddr_ll *) &s->local;
 	int ret;
@@ -161,7 +161,7 @@ int socket_open(struct node *n)
 
 int socket_reverse(struct node *n)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 	
 	SWAP(s->remote, s->local);
 	
@@ -170,7 +170,7 @@ int socket_reverse(struct node *n)
 
 int socket_close(struct node *n)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 
 	if (s->sd >= 0)
 		close(s->sd);
@@ -180,7 +180,7 @@ int socket_close(struct node *n)
 
 int socket_destroy(struct node *n)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 	
 	rtnl_qdisc_put(s->tc_qdisc);
 	rtnl_cls_put(s->tc_classifier);
@@ -190,7 +190,7 @@ int socket_destroy(struct node *n)
 
 int socket_read(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 
 	int bytes;
 	struct iovec iov[cnt];
@@ -249,7 +249,7 @@ int socket_read(struct node *n, struct msg *pool, int poolsize, int first, int c
 
 int socket_write(struct node *n, struct msg *pool, int poolsize, int first, int cnt)
 {
-	struct socket *s = n->socket;
+	struct socket *s = n->_vd;
 	int bytes, sent = 0;
 
 	/** @todo we should check the MTU */
@@ -296,7 +296,7 @@ int socket_parse(struct node *n, config_setting_t *cfg)
 	const char *local, *remote, *layer;
 	int ret;
 
-	struct socket *s = alloc(sizeof(struct socket));
+	struct socket *s = n->_vd;
 
 	if (!config_setting_lookup_string(cfg, "layer", &layer))
 		cerror(cfg, "Missing layer for node %s", node_name(n));
@@ -335,8 +335,6 @@ int socket_parse(struct node *n, config_setting_t *cfg)
 			tc_parse(cfg_netem, &s->tc_qdisc);
 	}
 
-	n->socket = s;
-
 	return 0;
 }
 
@@ -478,6 +476,7 @@ int socket_parse_addr(const char *addr, struct sockaddr *saddr, enum socket_laye
 static struct node_type vt = {
 	.name		= "socket",
 	.description	= "Network socket (libnl3)",
+	.size		= sizeof(struct socket),
 	.destroy	= socket_destroy,
 	.reverse	= socket_reverse,
 	.parse		= socket_parse,