diff --git a/src/apps/snmp/snmp_netconn.c b/src/apps/snmp/snmp_netconn.c
index aa83f391..440b461f 100644
--- a/src/apps/snmp/snmp_netconn.c
+++ b/src/apps/snmp/snmp_netconn.c
@@ -94,7 +94,7 @@ snmp_get_local_ip_for_dst(void* handle, const ip_addr_t *dst, ip_addr_t *result)
 
   LWIP_UNUSED_ARG(conn); /* unused in case of IPV4 only configuration */
 
-  ip_route_get_local_ip(IP_IS_V6_VAL(conn->pcb.udp->local_ip), &conn->pcb.udp->local_ip, dst, dst_if, dst_ip);
+  ip_route_get_local_ip(&conn->pcb.udp->local_ip, dst, dst_if, dst_ip);
 
   if((dst_if != NULL) && (dst_ip != NULL)) {
     ip_addr_copy(*result, *dst_ip);
diff --git a/src/apps/snmp/snmp_raw.c b/src/apps/snmp/snmp_raw.c
index 50a6ca07..2fb7765c 100644
--- a/src/apps/snmp/snmp_raw.c
+++ b/src/apps/snmp/snmp_raw.c
@@ -67,7 +67,7 @@ snmp_get_local_ip_for_dst(void* handle, const ip_addr_t *dst, ip_addr_t *result)
 
   LWIP_UNUSED_ARG(udp_pcb); /* unused in case of IPV4 only configuration */
 
-  ip_route_get_local_ip(IP_IS_V6_VAL(udp_pcb->local_ip), &udp_pcb->local_ip, dst, dst_if, dst_ip);
+  ip_route_get_local_ip(&udp_pcb->local_ip, dst, dst_if, dst_ip);
 
   if((dst_if != NULL) && (dst_ip != NULL)) {
     ip_addr_copy(*result, *dst_ip);
diff --git a/src/core/raw.c b/src/core/raw.c
index 6635d65e..b2c4d09c 100644
--- a/src/core/raw.c
+++ b/src/core/raw.c
@@ -279,7 +279,7 @@ raw_sendto(struct raw_pcb *pcb, struct pbuf *p, const ip_addr_t *ipaddr)
     }
   }
 
-  netif = ip_route(IP_IS_V6(dst_ip), &pcb->local_ip, dst_ip);
+  netif = ip_route(&pcb->local_ip, dst_ip);
   if (netif == NULL) {
     LWIP_DEBUGF(RAW_DEBUG | LWIP_DBG_LEVEL_WARNING, ("raw_sendto: No route to "));
     ip_addr_debug_print(RAW_DEBUG | LWIP_DBG_LEVEL_WARNING, dst_ip);
@@ -307,7 +307,7 @@ raw_sendto(struct raw_pcb *pcb, struct pbuf *p, const ip_addr_t *ipaddr)
 
   if (ip_addr_isany(&pcb->local_ip)) {
     /* use outgoing network interface IP address as source address */
-    src_ip = ip_netif_get_local_ip(IP_IS_V6(dst_ip), netif, dst_ip);
+    src_ip = ip_netif_get_local_ip(netif, dst_ip);
 #if LWIP_IPV6
     if (src_ip == NULL) {
       if (q != p) {
@@ -332,7 +332,7 @@ raw_sendto(struct raw_pcb *pcb, struct pbuf *p, const ip_addr_t *ipaddr)
 #endif
 
   NETIF_SET_HWADDRHINT(netif, &pcb->addr_hint);
-  err = ip_output_if(IP_IS_V6(dst_ip), q, src_ip, dst_ip, pcb->ttl, pcb->tos, pcb->protocol, netif);
+  err = ip_output_if(q, src_ip, dst_ip, pcb->ttl, pcb->tos, pcb->protocol, netif);
   NETIF_SET_HWADDRHINT(netif, NULL);
 
   /* did we chain a header earlier? */
diff --git a/src/core/tcp.c b/src/core/tcp.c
index 861e20aa..783db33c 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -763,11 +763,7 @@ tcp_connect(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port,
   LWIP_ERROR("tcp_connect: can only connect from state CLOSED", pcb->state == CLOSED, return ERR_ISCONN);
 
   LWIP_DEBUGF(TCP_DEBUG, ("tcp_connect to port %"U16_F"\n", port));
-  if (ipaddr != NULL) {
-    ip_addr_set(&pcb->remote_ip, ipaddr);
-  } else {
-    return ERR_VAL;
-  }
+  ip_addr_set(&pcb->remote_ip, ipaddr);
   pcb->remote_port = port;
 
   /* check if we have a route to the remote host */
@@ -775,7 +771,7 @@ tcp_connect(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port,
     /* no local IP address set, yet. */
     struct netif *netif;
     const ip_addr_t *local_ip;
-    ip_route_get_local_ip(IP_IS_V6(ipaddr), &pcb->local_ip, &pcb->remote_ip, netif, local_ip);
+    ip_route_get_local_ip(&pcb->local_ip, &pcb->remote_ip, netif, local_ip);
     if ((netif == NULL) || (local_ip == NULL)) {
       /* Don't even try to send a SYN packet if we have no route
          since that will fail. */
@@ -828,7 +824,7 @@ tcp_connect(struct tcp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port,
      The send MSS is updated when an MSS option is received. */
   pcb->mss = (TCP_MSS > 536) ? 536 : TCP_MSS;
 #if TCP_CALCULATE_EFF_SEND_MSS
-  pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip, IP_IS_V6_VAL(pcb->remote_ip));
+  pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip);
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
   pcb->cwnd = 1;
   pcb->ssthresh = TCP_WND;
@@ -1785,19 +1781,16 @@ tcp_eff_send_mss_impl(u16_t sendmss, const ip_addr_t *dest
 #if LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING
                      , const ip_addr_t *src
 #endif /* LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING */
-#if LWIP_IPV6 && LWIP_IPV4
-                     , u8_t isipv6
-#endif /* LWIP_IPV6 && LWIP_IPV4 */
                      )
 {
   u16_t mss_s;
   struct netif *outif;
   s16_t mtu;
 
-  outif = ip_route(isipv6, src, dest);
+  outif = ip_route(src, dest);
 #if LWIP_IPV6
 #if LWIP_IPV4
-  if (isipv6)
+  if (IP_IS_V6(dest))
 #endif /* LWIP_IPV4 */
   {
     /* First look in destination cache, to see if there is a Path MTU. */
@@ -1819,7 +1812,7 @@ tcp_eff_send_mss_impl(u16_t sendmss, const ip_addr_t *dest
   if (mtu != 0) {
 #if LWIP_IPV6
 #if LWIP_IPV4
-    if (isipv6)
+    if (IP_IS_V6(dest))
 #endif /* LWIP_IPV4 */
     {
       mss_s = mtu - IP6_HLEN - TCP_HLEN;
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index b719435b..0dccad22 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -594,8 +594,7 @@ tcp_listen_input(struct tcp_pcb_listen *pcb)
     npcb->ssthresh = LWIP_TCP_INITIAL_SSTHRESH(npcb);
 
 #if TCP_CALCULATE_EFF_SEND_MSS
-    npcb->mss = tcp_eff_send_mss(npcb->mss, &npcb->local_ip,
-      &npcb->remote_ip, IP_IS_V6_VAL(npcb->remote_ip));
+    npcb->mss = tcp_eff_send_mss(npcb->mss, &npcb->local_ip, &npcb->remote_ip);
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
 
     MIB2_STATS_INC(mib2.tcppassiveopens);
@@ -736,8 +735,7 @@ tcp_process(struct tcp_pcb *pcb)
       pcb->state = ESTABLISHED;
 
 #if TCP_CALCULATE_EFF_SEND_MSS
-      pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip,
-        IP_IS_V6_VAL(pcb->remote_ip));
+      pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip);
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
 
       /* Set ssthresh again after changing 'mss' and 'snd_wnd' */
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 5de643fa..fa8d77fb 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -930,7 +930,7 @@ tcp_send_empty_ack(struct tcp_pcb *pcb)
   }
 #endif
 
-  netif = ip_route(IP_IS_V6_VAL(pcb->remote_ip), &pcb->local_ip, &pcb->remote_ip);
+  netif = ip_route(&pcb->local_ip, &pcb->remote_ip);
   if (netif == NULL) {
     err = ERR_RTE;
   } else {
@@ -941,7 +941,7 @@ tcp_send_empty_ack(struct tcp_pcb *pcb)
     }
 #endif
     NETIF_SET_HWADDRHINT(netif, &(pcb->addr_hint));
-    err = ip_output_if(IP_IS_V6_VAL(pcb->remote_ip), p, &pcb->local_ip, &pcb->remote_ip,
+    err = ip_output_if(p, &pcb->local_ip, &pcb->remote_ip,
       pcb->ttl, pcb->tos, IP_PROTO_TCP, netif);
     NETIF_SET_HWADDRHINT(netif, NULL);
   }
@@ -1161,7 +1161,7 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
   if (seg->flags & TF_SEG_OPTS_MSS) {
     u16_t mss;
 #if TCP_CALCULATE_EFF_SEND_MSS
-    mss = tcp_eff_send_mss(TCP_MSS, &pcb->local_ip, &pcb->remote_ip, IP_IS_V6_VAL(pcb->remote_ip));
+    mss = tcp_eff_send_mss(TCP_MSS, &pcb->local_ip, &pcb->remote_ip);
 #else /* TCP_CALCULATE_EFF_SEND_MSS */
     mss = TCP_MSS;
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
@@ -1189,15 +1189,14 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
     pcb->rtime = 0;
   }
 
-  netif = ip_route(IP_IS_V6_VAL(pcb->remote_ip), &pcb->local_ip, &pcb->remote_ip);
+  netif = ip_route(&pcb->local_ip, &pcb->remote_ip);
   if (netif == NULL) {
     return ERR_RTE;
   }
 
   /* If we don't have a local IP address, we get one from netif */
   if (ip_addr_isany(&pcb->local_ip)) {
-    const ip_addr_t *local_ip = ip_netif_get_local_ip(IP_IS_V6_VAL(pcb->remote_ip), netif,
-      &pcb->remote_ip);
+    const ip_addr_t *local_ip = ip_netif_get_local_ip(netif, &pcb->remote_ip);
     if (local_ip == NULL) {
       return ERR_RTE;
     }
@@ -1262,7 +1261,7 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
   TCP_STATS_INC(tcp.xmit);
 
   NETIF_SET_HWADDRHINT(netif, &(pcb->addr_hint));
-  err = ip_output_if(IP_IS_V6_VAL(pcb->remote_ip), seg->p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
+  err = ip_output_if(seg->p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
     pcb->tos, IP_PROTO_TCP, netif);
   NETIF_SET_HWADDRHINT(netif, NULL);
   return err;
@@ -1321,7 +1320,7 @@ tcp_rst(u32_t seqno, u32_t ackno,
   TCP_STATS_INC(tcp.xmit);
   MIB2_STATS_INC(mib2.tcpoutrsts);
 
-  netif = ip_route(IP_IS_V6(remote_ip), local_ip, remote_ip);
+  netif = ip_route(local_ip, remote_ip);
   if (netif != NULL) {
 #if CHECKSUM_GEN_TCP
     IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_TCP) {
@@ -1330,7 +1329,7 @@ tcp_rst(u32_t seqno, u32_t ackno,
     }
 #endif
     /* Send output with hardcoded TTL/HL since we have no access to the pcb */
-    ip_output_if(IP_IS_V6(remote_ip), p, local_ip, remote_ip, TCP_TTL, 0, IP_PROTO_TCP, netif);
+    ip_output_if(p, local_ip, remote_ip, TCP_TTL, 0, IP_PROTO_TCP, netif);
   }
   pbuf_free(p);
   LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_rst: seqno %"U32_F" ackno %"U32_F".\n", seqno, ackno));
@@ -1493,7 +1492,7 @@ tcp_keepalive(struct tcp_pcb *pcb)
                 ("tcp_keepalive: could not allocate memory for pbuf\n"));
     return ERR_MEM;
   }
-  netif = ip_route(IP_IS_V6_VAL(pcb->remote_ip), &pcb->local_ip, &pcb->remote_ip);
+  netif = ip_route(&pcb->local_ip, &pcb->remote_ip);
   if (netif == NULL) {
     err = ERR_RTE;
   } else {
@@ -1508,8 +1507,7 @@ tcp_keepalive(struct tcp_pcb *pcb)
 
     /* Send output to IP */
     NETIF_SET_HWADDRHINT(netif, &(pcb->addr_hint));
-    err = ip_output_if(IP_IS_V6_VAL(pcb->remote_ip), p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
-      0, IP_PROTO_TCP, netif);
+    err = ip_output_if(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP, netif);
     NETIF_SET_HWADDRHINT(netif, NULL);
   }
   pbuf_free(p);
@@ -1581,7 +1579,7 @@ tcp_zero_window_probe(struct tcp_pcb *pcb)
     pbuf_copy_partial(seg->p, d, 1, seg->p->tot_len - seg->len);
   }
 
-  netif = ip_route(IP_IS_V6_VAL(pcb->remote_ip), &pcb->local_ip, &pcb->remote_ip);
+  netif = ip_route(&pcb->local_ip, &pcb->remote_ip);
   if (netif == NULL) {
     err = ERR_RTE;
   } else {
@@ -1595,7 +1593,7 @@ tcp_zero_window_probe(struct tcp_pcb *pcb)
 
     /* Send output to IP */
     NETIF_SET_HWADDRHINT(netif, &(pcb->addr_hint));
-    err = ip_output_if(IP_IS_V6_VAL(pcb->remote_ip), p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
+    err = ip_output_if(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
       0, IP_PROTO_TCP, netif);
     NETIF_SET_HWADDRHINT(netif, NULL);
   }
diff --git a/src/core/udp.c b/src/core/udp.c
index 7327e6d9..6c3c5277 100644
--- a/src/core/udp.c
+++ b/src/core/udp.c
@@ -601,7 +601,7 @@ udp_sendto_chksum(struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *dst_ip,
 #endif /* LWIP_IPV6 || (LWIP_IPV4 && LWIP_MULTICAST_TX_OPTIONS) */
 
   /* find the outgoing network interface for this packet */
-  netif = ip_route(IP_IS_V6(dst_ip_route), &pcb->local_ip, dst_ip_route);
+  netif = ip_route(&pcb->local_ip, dst_ip_route);
 
   /* no outgoing network interface could be found? */
   if (netif == NULL) {
@@ -886,7 +886,7 @@ udp_sendto_if_src_chksum(struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *d
   LWIP_DEBUGF(UDP_DEBUG, ("udp_send: ip_output_if (,,,,0x%02"X16_F",)\n", (u16_t)ip_proto));
   /* output to IP */
   NETIF_SET_HWADDRHINT(netif, &(pcb->addr_hint));
-  err = ip_output_if_src(IP_IS_V6(dst_ip), q, src_ip, dst_ip, ttl, pcb->tos, ip_proto, netif);
+  err = ip_output_if_src(q, src_ip, dst_ip, ttl, pcb->tos, ip_proto, netif);
   NETIF_SET_HWADDRHINT(netif, NULL);
 
   /* TODO: must this be increased even if error occurred? */
diff --git a/src/include/lwip/ip.h b/src/include/lwip/ip.h
index 82fd657c..f1bb0ed7 100644
--- a/src/include/lwip/ip.h
+++ b/src/include/lwip/ip.h
@@ -225,63 +225,63 @@ extern struct ip_globals ip_data;
 #define ip_reset_option(pcb, opt) ((pcb)->so_options &= ~(opt))
 
 #if LWIP_IPV4 && LWIP_IPV6
-#define ip_output(isipv6, p, src, dest, ttl, tos, proto) \
-        ((isipv6) ? \
+#define ip_output(p, src, dest, ttl, tos, proto) \
+        (IP_IS_V6(dest) ? \
         ip6_output(p, ip_2_ip6(src), ip_2_ip6(dest), ttl, tos, proto) : \
         ip4_output(p, ip_2_ip4(src), ip_2_ip4(dest), ttl, tos, proto))
-#define ip_output_if(isipv6, p, src, dest, ttl, tos, proto, netif) \
-        ((isipv6) ? \
+#define ip_output_if(p, src, dest, ttl, tos, proto, netif) \
+        (IP_IS_V6(dest) ? \
         ip6_output_if(p, ip_2_ip6(src), ip_2_ip6(dest), ttl, tos, proto, netif) : \
         ip4_output_if(p, ip_2_ip4(src), ip_2_ip4(dest), ttl, tos, proto, netif))
-#define ip_output_if_src(isipv6, p, src, dest, ttl, tos, proto, netif) \
-        ((isipv6) ? \
+#define ip_output_if_src(p, src, dest, ttl, tos, proto, netif) \
+        (IP_IS_V6(dest) ? \
         ip6_output_if_src(p, ip_2_ip6(src), ip_2_ip6(dest), ttl, tos, proto, netif) : \
         ip4_output_if_src(p, ip_2_ip4(src), ip_2_ip4(dest), ttl, tos, proto, netif))
-#define ip_output_hinted(isipv6, p, src, dest, ttl, tos, proto, addr_hint) \
-        ((isipv6) ? \
+#define ip_output_hinted(p, src, dest, ttl, tos, proto, addr_hint) \
+        (IP_IS_V6(dest) ? \
         ip6_output_hinted(p, ip_2_ip6(src), ip_2_ip6(dest), ttl, tos, proto, addr_hint) : \
         ip4_output_hinted(p, ip_2_ip4(src), ip_2_ip4(dest), ttl, tos, proto, addr_hint))
-#define ip_route(isipv6, src, dest) \
-        ((isipv6) ? \
+#define ip_route(src, dest) \
+        (IP_IS_V6(dest) ? \
         ip6_route(ip_2_ip6(src), ip_2_ip6(dest)) : \
         ip4_route_src(ip_2_ip4(dest), ip_2_ip4(src)))
-#define ip_netif_get_local_ip(isipv6, netif, dest) ((isipv6) ? \
+#define ip_netif_get_local_ip(netif, dest) (IP_IS_V6(dest) ? \
         ip6_netif_get_local_ip(netif, ip_2_ip6(dest)) : \
         ip4_netif_get_local_ip(netif))
 #define ip_debug_print(is_ipv6, p) ((is_ipv6) ? ip6_debug_print(p) : ip4_debug_print(p))
 #elif LWIP_IPV4 /* LWIP_IPV4 && LWIP_IPV6 */
-#define ip_output(isipv6, p, src, dest, ttl, tos, proto) \
+#define ip_output(p, src, dest, ttl, tos, proto) \
         ip4_output(p, src, dest, ttl, tos, proto)
-#define ip_output_if(isipv6, p, src, dest, ttl, tos, proto, netif) \
+#define ip_output_if(p, src, dest, ttl, tos, proto, netif) \
         ip4_output_if(p, src, dest, ttl, tos, proto, netif)
-#define ip_output_if_src(isipv6, p, src, dest, ttl, tos, proto, netif) \
+#define ip_output_if_src(p, src, dest, ttl, tos, proto, netif) \
         ip4_output_if_src(p, src, dest, ttl, tos, proto, netif)
-#define ip_output_hinted(isipv6, p, src, dest, ttl, tos, proto, addr_hint) \
+#define ip_output_hinted(p, src, dest, ttl, tos, proto, addr_hint) \
         ip4_output_hinted(p, src, dest, ttl, tos, proto, addr_hint)
-#define ip_route(isipv6, src, dest) \
+#define ip_route(src, dest) \
         ip4_route_src(dest, src)
-#define ip_netif_get_local_ip(isipv6, netif, dest) \
+#define ip_netif_get_local_ip(netif, dest) \
         ip4_netif_get_local_ip(netif)
 #define ip_debug_print(is_ipv6, p) ip4_debug_print(p)
 #elif LWIP_IPV6 /* LWIP_IPV4 && LWIP_IPV6 */
-#define ip_output(isipv6, p, src, dest, ttl, tos, proto) \
+#define ip_output(p, src, dest, ttl, tos, proto) \
         ip6_output(p, src, dest, ttl, tos, proto)
-#define ip_output_if(isipv6, p, src, dest, ttl, tos, proto, netif) \
+#define ip_output_if(p, src, dest, ttl, tos, proto, netif) \
         ip6_output_if(p, src, dest, ttl, tos, proto, netif)
-#define ip_output_if_src(isipv6, p, src, dest, ttl, tos, proto, netif) \
+#define ip_output_if_src(p, src, dest, ttl, tos, proto, netif) \
         ip6_output_if_src(p, src, dest, ttl, tos, proto, netif)
-#define ip_output_hinted(isipv6, p, src, dest, ttl, tos, proto, addr_hint) \
+#define ip_output_hinted(p, src, dest, ttl, tos, proto, addr_hint) \
         ip6_output_hinted(p, src, dest, ttl, tos, proto, addr_hint)
-#define ip_route(isipv6, src, dest) \
+#define ip_route(src, dest) \
         ip6_route(src, dest)
-#define ip_netif_get_local_ip(isipv6, netif, dest) \
+#define ip_netif_get_local_ip(netif, dest) \
         ip6_netif_get_local_ip(netif, dest)
 #define ip_debug_print(is_ipv6, p) ip6_debug_print(p)
 #endif /* LWIP_IPV6 */
 
-#define ip_route_get_local_ip(isipv6, src, dest, netif, ipaddr) do { \
-  (netif) = ip_route(isipv6, src, dest); \
-  (ipaddr) = ip_netif_get_local_ip(isipv6, netif, dest); \
+#define ip_route_get_local_ip(src, dest, netif, ipaddr) do { \
+  (netif) = ip_route(src, dest); \
+  (ipaddr) = ip_netif_get_local_ip(netif, dest); \
 }while(0)
 
 err_t ip_input(struct pbuf *p, struct netif *inp);
diff --git a/src/include/lwip/priv/tcp_priv.h b/src/include/lwip/priv/tcp_priv.h
index 0ed616e2..b5261b44 100644
--- a/src/include/lwip/priv/tcp_priv.h
+++ b/src/include/lwip/priv/tcp_priv.h
@@ -502,17 +502,12 @@ u16_t tcp_eff_send_mss_impl(u16_t sendmss, const ip_addr_t *dest
 #if LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING
                            , const ip_addr_t *src
 #endif /* LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING */
-#if LWIP_IPV6 && LWIP_IPV4
-                           , u8_t isipv6
-#endif /* LWIP_IPV6 && LWIP_IPV4 */
                            );
-#if LWIP_IPV4 && LWIP_IPV6
-#define tcp_eff_send_mss(sendmss, src, dest, isipv6) tcp_eff_send_mss_impl(sendmss, dest, src, isipv6)
-#elif LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING
-#define tcp_eff_send_mss(sendmss, src, dest, isipv6) tcp_eff_send_mss_impl(sendmss, dest, src)
-#else /* LWIP_IPV4 && LWIP_IPV6 */
-#define tcp_eff_send_mss(sendmss, src, dest, isipv6) tcp_eff_send_mss_impl(sendmss, dest)
-#endif /* LWIP_IPV4 && LWIP_IPV6 */
+#if LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING
+#define tcp_eff_send_mss(sendmss, src, dest) tcp_eff_send_mss_impl(sendmss, dest, src)
+#else /* LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING */
+#define tcp_eff_send_mss(sendmss, src, dest) tcp_eff_send_mss_impl(sendmss, dest)
+#endif /* LWIP_IPV6 || LWIP_IPV4_SRC_ROUTING */
 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
 
 #if LWIP_CALLBACK_API