diff --git a/conf.c b/conf.c
index cddc769..943526d 100644
--- a/conf.c
+++ b/conf.c
@@ -630,17 +630,17 @@ static void conf_ip(struct ctx *c)
 		v4 = v6		= IP_VERSION_PROBE;
 	}
 
-	if (!c->ifi)
-		c->ifi = nl_get_ext_if(&v4, &v6);
+	if (!c->ifi4 && !c->ifi6)
+		c->ifi4 = c->ifi6 = nl_get_ext_if(&v4, &v6);
 
 	if (v4 != IP_VERSION_DISABLED) {
 		if (!c->gw4)
-			nl_route(0, c->ifi, AF_INET, &c->gw4);
+			nl_route(0, c->ifi4, AF_INET, &c->gw4);
 
 		if (!c->addr4) {
 			int mask_len = 0;
 
-			nl_addr(0, c->ifi, AF_INET, &c->addr4, &mask_len, NULL);
+			nl_addr(0, c->ifi4, AF_INET, &c->addr4, &mask_len, NULL);
 			c->mask4 = htonl(0xffffffff << (32 - mask_len));
 		}
 
@@ -658,7 +658,7 @@ static void conf_ip(struct ctx *c)
 		memcpy(&c->addr4_seen, &c->addr4, sizeof(c->addr4_seen));
 
 		if (!memcmp(c->mac, MAC_ZERO, ETH_ALEN))
-			nl_link(0, c->ifi, c->mac, 0, 0);
+			nl_link(0, c->ifi4, c->mac, 0, 0);
 	}
 
 	if (c->mode == MODE_PASST)
@@ -668,9 +668,9 @@ static void conf_ip(struct ctx *c)
 		int prefix_len = 0;
 
 		if (IN6_IS_ADDR_UNSPECIFIED(&c->gw6))
-			nl_route(0, c->ifi, AF_INET6, &c->gw6);
+			nl_route(0, c->ifi6, AF_INET6, &c->gw6);
 
-		nl_addr(0, c->ifi, AF_INET6,
+		nl_addr(0, c->ifi6, AF_INET6,
 			IN6_IS_ADDR_UNSPECIFIED(&c->addr6) ? &c->addr6 : NULL,
 			&prefix_len, &c->addr6_ll);
 
@@ -883,12 +883,12 @@ static void conf_print(const struct ctx *c)
 	char buf4[INET_ADDRSTRLEN], ifn[IFNAMSIZ];
 	int i;
 
-	if (c->mode == MODE_PASTA) {
-		info("Outbound interface: %s, namespace interface: %s",
-		     if_indextoname(c->ifi, ifn), c->pasta_ifn);
-	} else {
-		info("Outbound interface: %s", if_indextoname(c->ifi, ifn));
-	}
+	if (c->ifi4)
+		info("Outbound interface (IPv4): %s", if_indextoname(c->ifi4, ifn));
+	if (c->ifi6)
+		info("Outbound interface (IPv6): %s", if_indextoname(c->ifi6, ifn));
+	if (c->mode == MODE_PASTA)
+		info("Namespace interface: %s", c->pasta_ifn);
 
 	if (c->v4) {
 		info("ARP:");
@@ -1395,12 +1395,12 @@ void conf(struct ctx *c, int argc, char **argv)
 			usage(argv[0]);
 			break;
 		case 'i':
-			if (c->ifi) {
+			if (c->ifi4 || c->ifi6) {
 				err("Redundant interface: %s", optarg);
 				usage(argv[0]);
 			}
 
-			if (!(c->ifi = if_nametoindex(optarg))) {
+			if (!(c->ifi4 = c->ifi6 = if_nametoindex(optarg))) {
 				err("Invalid interface name %s: %s", optarg,
 				    strerror(errno));
 				usage(argv[0]);
@@ -1559,8 +1559,12 @@ void conf(struct ctx *c, int argc, char **argv)
 
 	get_dns(c);
 
-	if (!*c->pasta_ifn)
-		if_indextoname(c->ifi, c->pasta_ifn);
+	if (!*c->pasta_ifn) {
+		if (c->ifi4)
+			if_indextoname(c->ifi4, c->pasta_ifn);
+		else
+			if_indextoname(c->ifi6, c->pasta_ifn);
+	}
 
 	c->tcp.ns_detect_ports   = c->udp.ns_detect_ports   = 0;
 	c->tcp.init_detect_ports = c->udp.init_detect_ports = 0;
diff --git a/passt.h b/passt.h
index e541341..23145c6 100644
--- a/passt.h
+++ b/passt.h
@@ -122,6 +122,7 @@ enum passt_modes {
  * @mac:		Host MAC address
  * @mac_guest:		MAC address of guest or namespace, seen or configured
  * @v4:			Enable IPv4 transport
+ * @ifi4:		Index of routable interface for IPv4
  * @addr4:		IPv4 address for external, routable interface
  * @addr4_seen:		Latest IPv4 address seen as source from tap
  * @mask4:		IPv4 netmask, network order
@@ -130,6 +131,7 @@ enum passt_modes {
  * @dns4_fwd:		Address forwarded (UDP) to first IPv4 DNS, network order
  * @dns_search:		DNS search list
  * @v6:			Enable IPv6 transport
+ * @ifi6:		Index of routable interface for IPv6
  * @addr6:		IPv6 address for external, routable interface
  * @addr6_ll:		Link-local IPv6 address on external, routable interface
  * @addr6_seen:		Latest IPv6 global/site address seen as source from tap
@@ -137,7 +139,6 @@ enum passt_modes {
  * @gw6:		Default IPv6 gateway
  * @dns6:		IPv6 DNS addresses, zero-terminated
  * @dns6_fwd:		Address forwarded (UDP) to first IPv6 DNS, network order
- * @ifi:		Index of routable interface
  * @pasta_ifn:		Name of namespace interface for pasta
  * @pasta_ifn:		Index of namespace interface for pasta
  * @pasta_conf_ns:	Configure namespace interface after creating it
@@ -193,6 +194,7 @@ struct ctx {
 	unsigned char mac_guest[ETH_ALEN];
 
 	int v4;
+	unsigned int ifi4;
 	uint32_t addr4;
 	uint32_t addr4_seen;
 	uint32_t mask4;
@@ -203,6 +205,7 @@ struct ctx {
 	struct fqdn dns_search[MAXDNSRCH];
 
 	int v6;
+	unsigned int ifi6;
 	struct in6_addr addr6;
 	struct in6_addr addr6_ll;
 	struct in6_addr addr6_seen;
@@ -211,7 +214,6 @@ struct ctx {
 	struct in6_addr dns6[MAXNS + 1];
 	struct in6_addr dns6_fwd;
 
-	unsigned int ifi;
 	char pasta_ifn[IF_NAMESIZE];
 	unsigned int pasta_ifi;
 	int pasta_conf_ns;
diff --git a/tcp.c b/tcp.c
index 5b84110..3b27f11 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2207,7 +2207,7 @@ static void tcp_conn_from_tap(struct ctx *c, int af, const void *addr,
 		struct sockaddr_in6 addr6_ll = {
 			.sin6_family = AF_INET6,
 			.sin6_addr = c->addr6_ll,
-			.sin6_scope_id = c->ifi,
+			.sin6_scope_id = c->ifi6,
 		};
 		if (bind(s, (struct sockaddr *)&addr6_ll, sizeof(addr6_ll))) {
 			close(s);
diff --git a/util.c b/util.c
index 2eea0ef..f4ec102 100644
--- a/util.c
+++ b/util.c
@@ -280,7 +280,7 @@ int sock_l4(const struct ctx *c, int af, uint8_t proto,
 
 			if (!memcmp(bind_addr, &c->addr6_ll,
 			    sizeof(c->addr6_ll)))
-				addr6.sin6_scope_id = c->ifi;
+				addr6.sin6_scope_id = c->ifi6;
 		} else {
 			addr6.sin6_addr = in6addr_any;
 		}