@@ -720,7 +720,7 @@ new config variables:

          dropping the connection. Linux only.

   tcp_crlf_ping = yes | no (set by default) - enable CRLF keepalives aka

          SIP outbound.

-  pmtu_discovery = 0 | 1 (default 0) - set DF bit in outbound IP if enabled

+  pmtu_discovery = 0 | 1 (default 0) - set DF bit in outbound IPv4 if enabled

   dns_srv_lb = yes | no (default no) - enable dns srv weight based load 

     balancing (see doc/dns.txt)

   dns_try_naptr = yes | no (default no) - enable naptr support 

@@ -329,22 +329,46 @@ int udp_init(struct socket_info* sock_info)

 	}

 #if defined (__OS_linux) && defined(UDP_ERRORS)

+	/* Ask for the ability to recvmsg (...,MSG_ERRQUEUE) for immediate

+	 * resend when hitting Path MTU limits. */

 	optval=1;

 	/* enable error receiving on unconnected sockets */

-	if(setsockopt(sock_info->socket, SOL_IP, IP_RECVERR,

+	if (addr->s.sa_family==AF_INET){

+		if(setsockopt(sock_info->socket, SOL_IP, IP_RECVERR,

 					(void*)&optval, sizeof(optval)) ==-1){

-		LM_ERR("setsockopt: %s\n", strerror(errno));

-		goto error;

+			LM_ERR("setsockopt: %s\n", strerror(errno));

+			goto error;

+		}

+	} else if (addr->s.sa_family==AF_INET6){

+		if(setsockopt(sock_info->socket, SOL_IPV6, IPV6_RECVERR,

+					(void*)&optval, sizeof(optval)) ==-1){

+			LM_ERR("setsockopt: %s\n", strerror(errno));

+			goto error;

+		}

 	}

 #endif

 #if defined (__OS_linux)

-	/* if pmtu_discovery=1 then set DF bit and do Path MTU discovery

-	 * disabled by default */

-	optval= (pmtu_discovery) ? IP_PMTUDISC_DO : IP_PMTUDISC_DONT;

-	if(setsockopt(sock_info->socket, IPPROTO_IP, IP_MTU_DISCOVER,

-			(void*)&optval, sizeof(optval)) ==-1){

-		LM_ERR("setsockopt: %s\n", strerror(errno));

-		goto error;

+	if (addr->s.sa_family==AF_INET){

+		/* If pmtu_discovery=1 then set DF bit and do Path MTU discovery

+		 * disabled by default.  Specific to IPv4. */

+		optval= (pmtu_discovery) ? IP_PMTUDISC_DO : IP_PMTUDISC_DONT;

+		if(setsockopt(sock_info->socket, IPPROTO_IP, IP_MTU_DISCOVER,

+				(void*)&optval, sizeof(optval)) ==-1){

+			LM_ERR("setsockopt: %s\n", strerror(errno));

+			goto error;

+		}

+	} else if (addr->s.sa_family==AF_INET6){

+		/* Since IPv6 never fragments but sends ICMPv6 Packet too Big,

+		 * we always want to benefit from kernel Path MTU knowledge;

+		 * especially because our sockets are unconnected and cannot

+		 * learn this for themselves.  Details in Issue #3119.  */

+		optval= IPV6_PMTUDISC_WANT;

+		if(setsockopt(sock_info->socket, IPPROTO_IPV6,

+				IPV6_MTU_DISCOVER,

+				(void*)&optval, sizeof(optval)) ==-1){

+			LM_ERR("setsockopt: %s\n", strerror(errno));

+			goto error;

+		}

 	}

 #endif