--- ./src/dns_internal.cc	2010-08-01 22:01:37.000000000 +0800
+++ ./src/dns_internal.cc	2010-08-10 19:31:46.000000000 +0800
@@ -201,10 +201,15 @@ 
 
     if (A.IsAnyAddr()) {
         debugs(78, 0, "WARNING: Squid does not accept " << A << " in DNS server specifications.");
-        A = "127.0.0.1";
+        A.SetLocalhost();
         debugs(78, 0, "Will be using " << A << " instead, assuming you meant that DNS is running on the same machine");
     }
 
+    if (!Ip::EnableIpv6 && !A.SetIPv4()) {
+        debugs(78, DBG_IMPORTANT, "WARNING: IPv6 is disabled. Discarding " << A << " in DNS server specifications.");
+        return;
+    }
+
     if (nns == nns_alloc) {
         int oldalloc = nns_alloc;
         ns *oldptr = nameservers;
@@ -742,6 +747,12 @@ 
     else
         addr = Config.Addrs.udp_incoming;
 
+    if (nameservers[ns].S.IsIPv4() && !addr.SetIPv4()) {
+        debugs(31, DBG_CRITICAL, "ERROR: Cannot contact DNS nameserver " << nameservers[ns].S << " from " << addr);
+        addr.SetAnyAddr();
+        addr.SetIPv4();
+    }
+
     vc->queue = new MemBuf;
 
     vc->msg = new MemBuf;
--- ./src/forward.cc	2010-08-01 22:01:37.000000000 +0800
+++ ./src/forward.cc	2010-08-10 19:31:46.000000000 +0800
@@ -870,9 +870,9 @@ 
 
     // if IPv6 is disabled try to force IPv4-only outgoing.
     if (!Ip::EnableIpv6 && !outgoing.SetIPv4()) {
-        debugs(50, 4, "fwdConnectStart: " << xstrerror());
+        debugs(50, 4, "fwdConnectStart: IPv6 is Disabled. Cannot connect from " << outgoing);
         ErrorState *anErr = errorCon(ERR_CONNECT_FAIL, HTTP_SERVICE_UNAVAILABLE, request);
-        anErr->xerrno = errno;
+        anErr->xerrno = EAFNOSUPPORT;
         fail(anErr);
         self = NULL;	// refcounted
         return;
--- ./src/neighbors.cc	2010-08-01 22:01:38.000000000 +0800
+++ ./src/neighbors.cc	2010-08-10 19:49:16.000000000 +0800
@@ -46,6 +46,7 @@ 
 #include "Store.h"
 #include "icmp/net_db.h"
 #include "ip/IpAddress.h"
+#include "ip/tools.h"
 
 /* count mcast group peers every 15 minutes */
 #define MCAST_COUNT_RATE 900
@@ -1387,6 +1388,20 @@ 
 
     IpAddress temp(getOutgoingAddr(NULL,p));
 
+    // if IPv6 is disabled try to force IPv4-only outgoing.
+    if (!Ip::EnableIpv6 && !temp.SetIPv4()) {
+        debugs(50, DBG_IMPORTANT, "WARNING: IPv6 is disabled. Failed to use " << temp << " to probe " << p->host);
+        return ret;
+    }
+
+    // if IPv6 is split-stack, prefer IPv4
+    if (Ip::EnableIpv6&IPV6_SPECIAL_SPLITSTACK) {
+        // NP: This is not a great choice of default,
+        // but with the current Internet being IPv4-majority has a higher success rate.
+        // if setting to IPv4 fails we dont care, that just means to use IPv6 outgoing.
+        temp.SetIPv4();
+    }
+
     fd = comm_open(SOCK_STREAM, IPPROTO_TCP, temp, COMM_NONBLOCKING, p->host);
 
     if (fd < 0)
--- ./src/tunnel.cc	2010-08-01 22:01:38.000000000 +0800
+++ ./src/tunnel.cc	2010-08-10 20:02:46.000000000 +0800
@@ -46,6 +46,7 @@ 
 #include "client_side.h"
 #include "MemBuf.h"
 #include "http.h"
+#include "ip/tools.h"
 
 class TunnelStateData
 {
@@ -641,6 +642,24 @@ 
     statCounter.server.other.requests++;
     /* Create socket. */
     IpAddress temp = getOutgoingAddr(request,NULL);
+
+    // if IPv6 is disabled try to force IPv4-only outgoing.
+    if (!Ip::EnableIpv6 && !temp.SetIPv4()) {
+        debugs(50, 4, "tunnelStart: IPv6 is Disabled. Tunnel failed from " << temp);
+        err = errorCon(ERR_CONNECT_FAIL, HTTP_SERVICE_UNAVAILABLE, request);
+        err->xerrno = EAFNOSUPPORT;
+        errorSend(fd, err);
+        return;
+    }
+
+    // if IPv6 is split-stack, prefer IPv4
+    if (Ip::EnableIpv6&IPV6_SPECIAL_SPLITSTACK) {
+        // NP: This is not a great choice of default,
+        // but with the current Internet being IPv4-majority has a higher success rate.
+        // if setting to IPv4 fails we dont care, that just means to use IPv6 outgoing.
+        temp.SetIPv4();
+    }
+
     int flags = COMM_NONBLOCKING;
     if (request->flags.spoof_client_ip) {
         flags |= COMM_TRANSPARENT;