diff --git a/Signal/src/network/IpAddress.h b/Signal/src/network/IpAddress.h
index d6c66438f..5a6759fdf 100644
--- a/Signal/src/network/IpAddress.h
+++ b/Signal/src/network/IpAddress.h
@@ -27,6 +27,9 @@
 +(IpAddress*) ipv4AddressFromSockaddr:(struct sockaddr_in)sockaddr;
 +(IpAddress*) ipv6AddressFromSockaddr:(struct sockaddr_in6)sockaddr;
 
+@property (nonatomic, readonly) bool isIpv4;
+@property (nonatomic, readonly) bool isIpv6;
+
 -(IpEndPoint*) withPort:(in_port_t)port;
 -(NSData*) sockaddrData;
 -(NSData*) sockaddrDataWithPort:(in_port_t)port;
diff --git a/Signal/src/network/IpAddress.m b/Signal/src/network/IpAddress.m
index 9f278d419..f1d4f2dc5 100644
--- a/Signal/src/network/IpAddress.m
+++ b/Signal/src/network/IpAddress.m
@@ -80,6 +80,16 @@
     return a;
 }
 
+- (bool)isIpv4
+{
+    return isIpv4;
+}
+
+- (bool)isIpv6
+{
+    return isIpv6;
+}
+
 -(IpEndPoint*) withPort:(in_port_t)port {
     return [IpEndPoint ipEndPointAtAddress:self onPort:port];
 }
diff --git a/Signal/src/network/IpEndPoint.h b/Signal/src/network/IpEndPoint.h
index 319baf150..e8fad928d 100644
--- a/Signal/src/network/IpEndPoint.h
+++ b/Signal/src/network/IpEndPoint.h
@@ -21,12 +21,15 @@
 +(IpEndPoint*) ipEndPointAtAddress:(IpAddress*)address
                             onPort:(in_port_t)port;
 
-+(IpEndPoint*) ipEndPointAtUnspecifiedAddressOnPort:(in_port_t)port;
++ (IpEndPoint *)ipv4EndPointAtUnspecifiedAddressOnPort:(in_port_t)port;
++ (IpEndPoint *)ipv6EndPointAtUnspecifiedAddressOnPort:(in_port_t)port;
 
 +(IpEndPoint*) ipEndPointFromSockaddrData:(NSData*)sockaddrData;
 +(IpEndPoint*) ipv4EndPointFromSockaddrData:(NSData*)sockaddrData;
 +(IpEndPoint*) ipv6EndPointFromSockaddrData:(NSData*)sockaddrData;
 
+- (IpEndPoint *)correspondingLocalEndpointWithPort:(in_port_t)specifiedLocalPort;
+
 -(in_port_t) port;
 -(IpAddress*) address;
 -(NSData*) sockaddrData;
diff --git a/Signal/src/network/IpEndPoint.m b/Signal/src/network/IpEndPoint.m
index a6fd85ef9..4c4f9bbc6 100644
--- a/Signal/src/network/IpEndPoint.m
+++ b/Signal/src/network/IpEndPoint.m
@@ -14,7 +14,8 @@
     return p;
 }
 
-+(IpEndPoint*) ipEndPointAtUnspecifiedAddressOnPort:(in_port_t)port {
++ (IpEndPoint *)ipv4EndPointAtUnspecifiedAddressOnPort:(in_port_t)port
+{
     struct sockaddr_in s;
     memset(&s, 0, sizeof(struct sockaddr_in));
     s.sin_len = sizeof(struct sockaddr_in);
@@ -27,6 +28,20 @@
     return a;
 }
 
++ (IpEndPoint *)ipv6EndPointAtUnspecifiedAddressOnPort:(in_port_t)port
+{
+    struct sockaddr_in6 address;
+    bzero(&address, sizeof(address));
+    address.sin6_len = sizeof(address);
+    address.sin6_family = AF_INET6;
+    address.sin6_port = htons(port);
+
+    IpEndPoint *a = [IpEndPoint new];
+    a->address = [IpAddress ipv6AddressFromString:@"0:0:0:0:0:0:0:0"];
+    a->port = port;
+    return a;
+}
+
 +(IpEndPoint*) ipEndPointFromSockaddrData:(NSData*)sockaddrData {
     ows_require(sockaddrData != nil);
     ows_require(sockaddrData.length >= sizeof(struct sockaddr));
@@ -59,6 +74,17 @@
     return [[IpAddress ipv6AddressFromSockaddr:s] withPort:ntohs(s.sin6_port)];
 }
 
+- (IpEndPoint *)correspondingLocalEndpointWithPort:(in_port_t)specifiedLocalPort
+{
+    if (self.address.isIpv4) {
+        DDLogDebug(@"%@ Connecting via IPv4", self.tag);
+        return [IpEndPoint ipv4EndPointAtUnspecifiedAddressOnPort:specifiedLocalPort];
+    } else {
+        DDLogDebug(@"%@ Connecting via IPv6", self.tag);
+        return [IpEndPoint ipv6EndPointAtUnspecifiedAddressOnPort:specifiedLocalPort];
+    }
+}
+
 -(IpAddress*) address {
     return address;
 }
@@ -92,4 +118,16 @@
     return [TOCFuture futureWithResult:@[self]];
 }
 
+#pragma mark - Logging
+
++ (NSString *)tag
+{
+    return [NSString stringWithFormat:@"[%@]", self.class];
+}
+
+- (NSString *)tag
+{
+    return self.class.tag;
+}
+
 @end
diff --git a/Signal/src/network/udp/UdpSocket.m b/Signal/src/network/udp/UdpSocket.m
index 024a3b47a..a2c6de136 100644
--- a/Signal/src/network/udp/UdpSocket.m
+++ b/Signal/src/network/udp/UdpSocket.m
@@ -1,6 +1,7 @@
 #import "Constraints.h"
 #import "ThreadManager.h"
 #import "UdpSocket.h"
+#import "IPAddress.h"
 
 @implementation UdpSocket
 
@@ -131,8 +132,14 @@ void onReceivedData(CFSocketRef socket, CFSocketCallBackType type, CFDataRef add
 }
 
 -(void) setupLocalEndPoint {
-    IpEndPoint* specifiedLocalEndPoint = [IpEndPoint ipEndPointAtUnspecifiedAddressOnPort:specifiedLocalPort];
-    
+    IpEndPoint *specifiedLocalEndPoint;
+    if (self.isRemoteEndPointKnown) {
+        specifiedLocalEndPoint = [specifiedRemoteEndPoint correspondingLocalEndpointWithPort:specifiedLocalPort];
+    } else {
+        DDLogWarn(@"%@ no remote end point. This is only used in unit tests.", self.tag);
+        specifiedLocalEndPoint = [IpEndPoint ipv4EndPointAtUnspecifiedAddressOnPort:specifiedLocalPort];
+    }
+
     CFSocketError setAddressResult = CFSocketSetAddress(socket, (__bridge CFDataRef)[specifiedLocalEndPoint sockaddrData]);
     checkOperationDescribe(setAddressResult == kCFSocketSuccess,
                            ([NSString stringWithFormat:@"CFSocketSetAddress failed with error code: %ld", setAddressResult]));
@@ -165,9 +172,16 @@ void onReceivedData(CFSocketRef socket, CFSocketCallBackType type, CFDataRef add
     
     @try {
         CFSocketContext socketContext = { 0, (__bridge void *)self, CFRetain, CFRelease, CFCopyDescription };
-        
+
+        SInt32 protocolFamily;
+        if (self.isRemoteEndPointKnown) {
+            protocolFamily = specifiedRemoteEndPoint.address.isIpv4 ? PF_INET : PF_INET6;
+        } else {
+            DDLogWarn(@"Uknown remote endpoint. This is only used in testing.");
+            protocolFamily = PF_INET;
+        }
         socket = CFSocketCreate(kCFAllocatorDefault,
-                                PF_INET,
+                                protocolFamily,
                                 SOCK_DGRAM,
                                 IPPROTO_UDP,
                                 kCFSocketDataCallBack,
@@ -194,4 +208,16 @@ void onReceivedData(CFSocketRef socket, CFSocketCallBackType type, CFDataRef add
     }
 }
 
+#pragma mark - Logging
+
++ (NSString *)tag
+{
+    return [NSString stringWithFormat:@"[%@]", self.class];
+}
+
+- (NSString *)tag
+{
+    return self.class.tag;
+}
+
 @end