on IPv4 UDP turn off DF flag.

git-svn-id: file:///svn/unbound/trunk@1937 be551aaa-1e26-0410-a405-d3ace91eadb9

doc/Changelog

@@ -1,3 +1,6 @@
+11 December 2009: Wouter
+	- on IPv4 UDP turn off DF flag.
+
 10 December 2009: Wouter
 	- requirements.txt updated with design choice explanations.
 	- Reading fixes: fix to set unlame when child confirms parent glue,

services/listen_dnsport.c

@@ -251,6 +251,25 @@ create_udp_sock(int family, int socktype, struct sockaddr* addr,
 			return -1;
 		}
 # endif /* IPv6 MTU */
+	} else if(family == AF_INET) {
+#  if defined(IP_MTU_DISCOVER) && defined(IP_PMTUDISC_DONT)
+		int action = IP_PMTUDISC_DONT;
+		if (setsockopt(s, IPPROTO_IP, IP_MTU_DISCOVER, 
+			&action, (socklen_t)sizeof(action)) < 0) {
+			log_err("setsockopt(..., IP_MTU_DISCOVER, "
+				"IP_PMTUDISC_DONT...) failed: %s",
+				strerror(errno));
+			return -1;
+		}
+#  elif defined(IP_DONTFRAG)
+		int off = 0;
+		if (setsockopt(s, IPPROTO_IP, IP_DONTFRAG, 
+			&off, (socklen_t)sizeof(off)) < 0) {
+			log_err("setsockopt(..., IP_DONTFRAG, ...) failed: %s",
+				strerror(errno));
+			return -1;
+		}
+#  endif /* IPv4 MTU */
 	}
 	if(bind(s, (struct sockaddr*)addr, addrlen) != 0) {
 		*noproto = 0;