diff --git a/scripts/base/frameworks/communication/main.bro b/scripts/base/frameworks/communication/main.bro
index 04772f57aa..26ec9f41b8 100644
--- a/scripts/base/frameworks/communication/main.bro
+++ b/scripts/base/frameworks/communication/main.bro
@@ -2,6 +2,7 @@
 ##! and/or transfer events.
 
 @load base/frameworks/packet-filter
+@load base/utils/addrs
 
 module Communication;
 
@@ -10,7 +11,7 @@ export {
 	## The communication logging stream identifier.
 	redef enum Log::ID += { LOG };
 	
-	## Which interface to listen on (0.0.0.0 for any interface).
+	## Which interface to listen on (``0.0.0.0`` or ``[::]`` are wildcards).
 	const listen_interface = 0.0.0.0 &redef;
 	
 	## Which port to listen on.
@@ -19,6 +20,14 @@ export {
 	## This defines if a listening socket should use SSL.
 	const listen_ssl = F &redef;
 
+	## Defines if a listening socket can bind to IPv6 addresses.
+	const listen_ipv6 = F &redef;
+
+	## Defines the interval at which to retry binding to
+	## :bro:id:`listen_interface` on :bro:id:`listen_port` if it's already in
+	## use.
+	const listen_retry = 30 secs &redef;
+
 	## Default compression level.  Compression level is 0-9, with 0 = no 
 	## compression.
 	global compression_level = 0 &redef;
@@ -160,7 +169,7 @@ event remote_log(level: count, src: count, msg: string)
 # This is a core generated event.
 event remote_log_peer(p: event_peer, level: count, src: count, msg: string)
 	{
-	local rmsg = fmt("[#%d/%s:%d] %s", p$id, p$host, p$p, msg);
+	local rmsg = fmt("[#%d/%s:%d] %s", p$id, addr_to_uri(p$host), p$p, msg);
 	do_script_log_common(level, src, rmsg);
 	}
 
diff --git a/scripts/base/utils/addrs.bro b/scripts/base/utils/addrs.bro
index 415b9adfa9..08efd5281a 100644
--- a/scripts/base/utils/addrs.bro
+++ b/scripts/base/utils/addrs.bro
@@ -98,3 +98,18 @@ function find_ip_addresses(input: string): string_array
 		}
 	return output;
 	}
+
+## Returns the string representation of an IP address suitable for inclusion
+## in a URI.  For IPv4, this does no special formatting, but for IPv6, the
+## address is included in square brackets.
+##
+## a: the address to make suitable for URI inclusion.
+##
+## Returns: the string representation of *a* suitable for URI inclusion.
+function addr_to_uri(a: addr): string
+	{
+	if ( is_v4_addr(a) )
+		return fmt("%s", a);
+	else
+		return fmt("[%s]", a);
+	}
diff --git a/scripts/policy/frameworks/communication/listen.bro b/scripts/policy/frameworks/communication/listen.bro
index e366e5b4ff..609e8c91d6 100644
--- a/scripts/policy/frameworks/communication/listen.bro
+++ b/scripts/policy/frameworks/communication/listen.bro
@@ -8,5 +8,6 @@ module Communication;
 event bro_init() &priority=-10
 	{
 	enable_communication();
-	listen(listen_interface, listen_port, listen_ssl);
+	listen(listen_interface, listen_port, listen_ssl, listen_ipv6,
+	       listen_retry);
 	}
diff --git a/src/IPAddr.h b/src/IPAddr.h
index 8e1921e07b..447669d422 100644
--- a/src/IPAddr.h
+++ b/src/IPAddr.h
@@ -188,11 +188,16 @@ public:
 	 * IPv4 to IPv6 address mapping to return a full 16 bytes.
 	 *
 	 * @param bytes The pointer to a memory location in which the
-	 * raw bytes of the address are to be copied in network byte-order.
+	 * raw bytes of the address are to be copied.
+	 *
+	 * @param order The byte-order in which the returned raw bytes are copied.
+	 * The default is network order.
 	 */
-	void CopyIPv6(uint32_t* bytes) const
+	void CopyIPv6(uint32_t* bytes, ByteOrder order = Network) const
 		{
 		memcpy(bytes, in6.s6_addr, sizeof(in6.s6_addr));
+		if ( order == Host )
+			for ( unsigned int i = 0; i < 4; ++i ) bytes[i] = ntohl(bytes[i]);
 		}
 
 	/**
@@ -280,6 +285,19 @@ public:
 	 */
 	string AsString() const;
 
+	/**
+	 * Returns a string representation of the address suitable for inclusion
+	 * in an URI.  For IPv4 addresses, this is the same as AsString(), but
+	 * IPv6 addresses are encased in square brackets.
+	 */
+	string AsURIString() const
+		{
+		if ( GetFamily() == IPv4 )
+			return AsString();
+		else
+			return string("[") + AsString() + "]";
+		}
+
 	/**
 	 * Returns a host-order, plain hex string representation of the address.
 	 */
diff --git a/src/RemoteSerializer.cc b/src/RemoteSerializer.cc
index 61be8a9e8f..3abec00f59 100644
--- a/src/RemoteSerializer.cc
+++ b/src/RemoteSerializer.cc
@@ -147,6 +147,7 @@
 
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <netdb.h>
 #include <sys/wait.h>
 #include <netinet/in.h>
 #include <unistd.h>
@@ -195,7 +196,7 @@ extern "C" {
 
 // Gets incremented each time there's an incompatible change
 // to the communication internals.
-static const unsigned short PROTOCOL_VERSION = 0x07;
+static const unsigned short PROTOCOL_VERSION = 0x08;
 
 static const char MSG_NONE = 0x00;
 static const char MSG_VERSION = 0x01;
@@ -458,17 +459,6 @@ static inline char* fmt_uint32s(int nargs, va_list ap)
 	}
 #endif
 
-
-static inline const char* ip2a(uint32 ip)
-	{
-	static char buffer[32];
-	struct in_addr addr;
-
-	addr.s_addr = htonl(ip);
-
-	return bro_inet_ntop(AF_INET, &addr, buffer, 32);
-	}
-
 static pid_t child_pid = 0;
 
 // Return true if message type is sent by a peer (rather than the child
@@ -683,24 +673,20 @@ RemoteSerializer::PeerID RemoteSerializer::Connect(const IPAddr& ip,
 	if ( ! initialized )
 		reporter->InternalError("remote serializer not initialized");
 
-	if ( ip.GetFamily() == IPv6 )
-		Error("inter-Bro communication not supported over IPv6");
-
-	const uint32* bytes;
-	ip.GetBytes(&bytes);
-	uint32 ip4 = ntohl(*bytes);
-
 	if ( ! child_pid )
 		Fork();
 
-	Peer* p = AddPeer(ip4, port);
+	Peer* p = AddPeer(ip, port);
 	p->orig = true;
 
 	if ( our_class )
 		p->our_class = our_class;
 
-	if ( ! SendToChild(MSG_CONNECT_TO, p, 5, p->id,
-				ip4, port, uint32(retry), use_ssl) )
+	uint32 bytes[4];
+	ip.CopyIPv6(bytes, IPAddr::Host);
+
+	if ( ! SendToChild(MSG_CONNECT_TO, p, 8, p->id, bytes[0], bytes[1],
+	                   bytes[2], bytes[3], port, uint32(retry), use_ssl) )
 		{
 		RemovePeer(p);
 		return false;
@@ -1232,7 +1218,8 @@ bool RemoteSerializer::SendCapabilities(Peer* peer)
 	return caps ? SendToChild(MSG_CAPS, peer, 3, caps, 0, 0) : true;
 	}
 
-bool RemoteSerializer::Listen(const IPAddr& ip, uint16 port, bool expect_ssl)
+bool RemoteSerializer::Listen(const IPAddr& ip, uint16 port, bool expect_ssl,
+                              bool ipv6, double retry)
 	{
 	if ( ! using_communication )
 		return true;
@@ -1240,14 +1227,15 @@ bool RemoteSerializer::Listen(const IPAddr& ip, uint16 port, bool expect_ssl)
 	if ( ! initialized )
 		reporter->InternalError("remote serializer not initialized");
 
-	if ( ip.GetFamily() == IPv6 )
-		Error("inter-Bro communication not supported over IPv6");
+	if ( ! ipv6 && ip.GetFamily() == IPv6 &&
+	     ip != IPAddr("0.0.0.0") && ip != IPAddr("::") )
+		reporter->FatalError("Attempt to listen on address %s, but IPv6 communication disabled", ip.AsString().c_str());
 
-	const uint32* bytes;
-	ip.GetBytes(&bytes);
-	uint32 ip4 = ntohl(*bytes);
+	uint32 bytes[4];
+	ip.CopyIPv6(bytes, IPAddr::Host);
 
-	if ( ! SendToChild(MSG_LISTEN, 0, 3, ip4, port, expect_ssl) )
+	if ( ! SendToChild(MSG_LISTEN, 0, 8, bytes[0], bytes[1], bytes[2], bytes[3],
+	                   port, expect_ssl, ipv6, (uint32) retry) )
 		return false;
 
 	listening = true;
@@ -1784,7 +1772,7 @@ RecordVal* RemoteSerializer::MakePeerVal(Peer* peer)
 	RecordVal* v = new RecordVal(::peer);
 	v->Assign(0, new Val(uint32(peer->id), TYPE_COUNT));
 	// Sic! Network order for AddrVal, host order for PortVal.
-	v->Assign(1, new AddrVal(htonl(peer->ip)));
+	v->Assign(1, new AddrVal(peer->ip));
 	v->Assign(2, new PortVal(peer->port, TRANSPORT_TCP));
 	v->Assign(3, new Val(false, TYPE_BOOL));
 	v->Assign(4, new StringVal(""));	// set when received
@@ -1793,8 +1781,8 @@ RecordVal* RemoteSerializer::MakePeerVal(Peer* peer)
 	return v;
 	}
 
-RemoteSerializer::Peer* RemoteSerializer::AddPeer(uint32 ip, uint16 port,
-							PeerID id)
+RemoteSerializer::Peer* RemoteSerializer::AddPeer(const IPAddr& ip, uint16 port,
+                                                  PeerID id)
 	{
 	Peer* peer = new Peer;
 	peer->id = id != PEER_NONE ? id : id_counter++;
@@ -1960,8 +1948,8 @@ bool RemoteSerializer::ProcessConnected()
 	{
 	// IP and port follow.
 	uint32* args = (uint32*) current_args->data;
-	uint32 host = ntohl(args[0]);	// ### Fix: only works for IPv4
-	uint16 port = (uint16) ntohl(args[1]);
+	IPAddr host = IPAddr(IPv6, args, IPAddr::Network);
+	uint16 port = (uint16) ntohl(args[4]);
 
 	if ( ! current_peer )
 		{
@@ -2980,7 +2968,8 @@ void RemoteSerializer::Log(LogLevel level, const char* msg, Peer* peer,
 
 	if ( peer )
 		len += snprintf(buffer + len, sizeof(buffer) - len, "[#%d/%s:%d] ",
-		                int(peer->id), ip2a(peer->ip), peer->port);
+		                int(peer->id), peer->ip.AsURIString().c_str(),
+		                peer->port);
 
 	len += safe_snprintf(buffer + len, sizeof(buffer) - len, "%s", msg);
 
@@ -3266,8 +3255,10 @@ SocketComm::SocketComm()
 	terminating = false;
 	killing = false;
 
-	listen_fd_clear = -1;
-	listen_fd_ssl = -1;
+	listen_port = 0;
+	listen_ssl = false;
+	enable_ipv6 = false;
+	bind_retry_interval = 0;
 	listen_next_try = 0;
 
 	// We don't want to use the signal handlers of our parent.
@@ -3290,8 +3281,7 @@ SocketComm::~SocketComm()
 		delete peers[i]->io;
 
 	delete io;
-	close(listen_fd_clear);
-	close(listen_fd_ssl);
+	CloseListenFDs();
 	}
 
 static unsigned int first_rtime = 0;
@@ -3340,20 +3330,13 @@ void SocketComm::Run()
 			}
 
 		if ( listen_next_try && time(0) > listen_next_try  )
-			Listen(listen_if, listen_port, listen_ssl);
+			Listen();
 
-		if ( listen_fd_clear >= 0 )
+		for ( size_t i = 0; i < listen_fds.size(); ++i )
 			{
-			FD_SET(listen_fd_clear, &fd_read);
-			if ( listen_fd_clear > max_fd )
-				max_fd = listen_fd_clear;
-			}
-
-		if ( listen_fd_ssl >= 0 )
-			{
-			FD_SET(listen_fd_ssl, &fd_read);
-			if ( listen_fd_ssl > max_fd )
-				max_fd = listen_fd_ssl;
+			FD_SET(listen_fds[i], &fd_read);
+			if ( listen_fds[i] > max_fd )
+				max_fd = listen_fds[i];
 			}
 
 		if ( io->IsFillingUp() && ! shutting_conns_down )
@@ -3442,12 +3425,9 @@ void SocketComm::Run()
 				}
 			}
 
-		if ( listen_fd_clear >= 0 &&
-		     FD_ISSET(listen_fd_clear, &fd_read) )
-			AcceptConnection(listen_fd_clear);
-
-		if ( listen_fd_ssl >= 0 && FD_ISSET(listen_fd_ssl, &fd_read) )
-			AcceptConnection(listen_fd_ssl);
+		for ( size_t i = 0; i < listen_fds.size(); ++i )
+			if ( FD_ISSET(listen_fds[i], &fd_read) )
+				AcceptConnection(listen_fds[i]);
 
 		// Hack to display CPU usage of the child, triggered via
 		// SIGPROF.
@@ -3571,13 +3551,8 @@ bool SocketComm::DoParentMessage()
 
 	case MSG_LISTEN_STOP:
 		{
-		if ( listen_fd_ssl >= 0 )
-			close(listen_fd_ssl);
+		CloseListenFDs();
 
-		if ( listen_fd_clear >= 0 )
-			close(listen_fd_clear);
-
-		listen_fd_clear = listen_fd_ssl = -1;
 		Log("stopped listening");
 
 		return true;
@@ -3721,10 +3696,10 @@ bool SocketComm::ProcessConnectTo()
 
 	Peer* peer = new Peer;
 	peer->id = ntohl(args[0]);
-	peer->ip = ntohl(args[1]);
-	peer->port = ntohl(args[2]);
-	peer->retry = ntohl(args[3]);
-	peer->ssl = ntohl(args[4]);
+	peer->ip = IPAddr(IPv6, &args[1], IPAddr::Network);
+	peer->port = ntohl(args[5]);
+	peer->retry = ntohl(args[6]);
+	peer->ssl = ntohl(args[7]);
 
 	return Connect(peer);
 	}
@@ -3734,11 +3709,13 @@ bool SocketComm::ProcessListen()
 	assert(parent_args);
 	uint32* args = (uint32*) parent_args->data;
 
-	uint32 addr = ntohl(args[0]);
-	uint16 port = uint16(ntohl(args[1]));
-	uint32 ssl = ntohl(args[2]);
+	listen_if = IPAddr(IPv6, args, IPAddr::Network);
+	listen_port = uint16(ntohl(args[4]));
+	listen_ssl = ntohl(args[5]) != 0;
+	enable_ipv6 = ntohl(args[6]) != 0;
+	bind_retry_interval = ntohl(args[7]);
 
-	return Listen(addr, port, ssl);
+	return Listen();
 	}
 
 bool SocketComm::ProcessParentCompress()
@@ -3900,29 +3877,53 @@ bool SocketComm::ProcessPeerCompress(Peer* peer)
 
 bool SocketComm::Connect(Peer* peer)
 	{
-	struct sockaddr_in server;
+	int status;
+	addrinfo hints, *res, *res0;
+	bzero(&hints, sizeof(hints));
 
-	int sockfd = socket(PF_INET, SOCK_STREAM, 0);
-	if ( sockfd < 0 )
+	hints.ai_family = PF_UNSPEC;
+	hints.ai_protocol = IPPROTO_TCP;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_flags = AI_NUMERICHOST;
+
+	char port_str[16];
+	modp_uitoa10(peer->port, port_str);
+
+	// TODO: better to accept string arguments from the user to pass into
+	// getaddrinfo? This might make it easier to explicitly connect to
+	// non-global IPv6 addresses with a scope zone identifier (RFC 4007).
+	status = getaddrinfo(peer->ip.AsString().c_str(), port_str, &hints, &res0);
+	if ( status != 0 )
 		{
-		Error(fmt("can't create socket, %s", strerror(errno)));
+		Error(fmt("getaddrinfo error: %s", gai_strerror(status)));
 		return false;
 		}
 
-	bzero(&server, sizeof(server));
-	server.sin_family = AF_INET;
-	server.sin_port = htons(peer->port);
-	server.sin_addr.s_addr = htonl(peer->ip);
-
-	bool connected = true;
-
-	if ( connect(sockfd, (sockaddr*) &server, sizeof(server)) < 0 )
+	int sockfd = -1;
+	for ( res = res0; res; res = res->ai_next )
 		{
-		Error(fmt("connect failed: %s", strerror(errno)), peer);
-		close(sockfd);
-		connected = false;
+		sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+		if ( sockfd < 0 )
+			{
+			Error(fmt("can't create connect socket, %s", strerror(errno)));
+			continue;
+			}
+
+		if ( connect(sockfd, res->ai_addr, res->ai_addrlen) < 0 )
+			{
+			Error(fmt("connect failed: %s", strerror(errno)), peer);
+			close(sockfd);
+			sockfd = -1;
+			continue;
+			}
+
+		break;
 		}
 
+	freeaddrinfo(res0);
+
+	bool connected = sockfd != -1;
+
 	if ( ! (connected || peer->retry) )
 		{
 		CloseConnection(peer, false);
@@ -3947,9 +3948,7 @@ bool SocketComm::Connect(Peer* peer)
 	if ( connected )
 		{
 		if ( peer->ssl )
-			{
 			peer->io = new ChunkedIOSSL(sockfd, false);
-			}
 		else
 			peer->io = new ChunkedIOFd(sockfd, "child->peer");
 
@@ -3964,7 +3963,12 @@ bool SocketComm::Connect(Peer* peer)
 	if ( connected )
 		{
 		Log("connected", peer);
-		if ( ! SendToParent(MSG_CONNECTED, peer, 2, peer->ip, peer->port) )
+
+		uint32 bytes[4];
+		peer->ip.CopyIPv6(bytes, IPAddr::Host);
+
+		if ( ! SendToParent(MSG_CONNECTED, peer, 5, bytes[0], bytes[1],
+		                    bytes[2], bytes[3], peer->port) )
 			return false;
 		}
 
@@ -4001,86 +4005,139 @@ bool SocketComm::CloseConnection(Peer* peer, bool reconnect)
 	return true;
 	}
 
-bool SocketComm::Listen(uint32 ip, uint16 port, bool expect_ssl)
+bool SocketComm::Listen()
 	{
-	int* listen_fd = expect_ssl ? &listen_fd_ssl : &listen_fd_clear;
+	int status, on = 1;
+	addrinfo hints, *res, *res0;
+	bzero(&hints, sizeof(hints));
 
-	if ( *listen_fd >= 0 )
-		close(*listen_fd);
-
-	struct sockaddr_in server;
-
-	*listen_fd = socket(PF_INET, SOCK_STREAM, 0);
-	if ( *listen_fd < 0 )
+	if ( enable_ipv6 )
 		{
-		Error(fmt("can't create listen socket, %s",
-				strerror(errno)));
+		if ( listen_if == IPAddr("0.0.0.0") || listen_if == IPAddr("::") )
+			hints.ai_family = PF_UNSPEC;
+		else
+			hints.ai_family = listen_if.GetFamily() == IPv4 ? PF_INET : PF_INET6;
+		}
+	else
+		hints.ai_family = PF_INET;
+
+	hints.ai_protocol = IPPROTO_TCP;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_flags = AI_PASSIVE | AI_ADDRCONFIG | AI_NUMERICHOST;
+
+	char port_str[16];
+	modp_uitoa10(listen_port, port_str);
+
+	const char* addr_str = 0;
+	if ( listen_if != IPAddr("0.0.0.0") && listen_if != IPAddr("::") )
+		addr_str = listen_if.AsString().c_str();
+
+	CloseListenFDs();
+
+	// TODO: better to accept string arguments from the user to pass into
+	// getaddrinfo?  This might make it easier to explicitly bind to a
+	// non-global IPv6 address with a scope zone identifier (RFC 4007).
+	if ( (status = getaddrinfo(addr_str, port_str, &hints, &res0)) != 0 )
+		{
+		Error(fmt("getaddrinfo error: %s", gai_strerror(status)));
 		return false;
 		}
 
-	// Set SO_REUSEADDR.
-	int turn_on = 1;
-	if ( setsockopt(*listen_fd, SOL_SOCKET, SO_REUSEADDR,
-			&turn_on, sizeof(turn_on)) < 0 )
+	for ( res = res0; res; res = res->ai_next )
 		{
-		Error(fmt("can't set SO_REUSEADDR, %s",
-				strerror(errno)));
-		return false;
-		}
-
-	bzero(&server, sizeof(server));
-	server.sin_family = AF_INET;
-	server.sin_port = htons(port);
-	server.sin_addr.s_addr = htonl(ip);
-
-	if ( bind(*listen_fd, (sockaddr*) &server, sizeof(server)) < 0 )
-		{
-		Error(fmt("can't bind to port %d, %s", port, strerror(errno)));
-		close(*listen_fd);
-		*listen_fd = -1;
-
-		if ( errno == EADDRINUSE )
+		if ( res->ai_family != AF_INET && res->ai_family != AF_INET6 )
 			{
-			listen_if = ip;
-			listen_port = port;
-			listen_ssl = expect_ssl;
-			// FIXME: Make this timeout configurable.
-			listen_next_try = time(0) + 30;
+			Error(fmt("can't create listen socket: unknown address family, %d",
+			          res->ai_family));
+			continue;
 			}
-		return false;
+
+		IPAddr a = res->ai_family == AF_INET ?
+				IPAddr(((sockaddr_in*)res->ai_addr)->sin_addr) :
+				IPAddr(((sockaddr_in6*)res->ai_addr)->sin6_addr);
+
+		int fd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+		if ( fd < 0 )
+			{
+			Error(fmt("can't create listen socket, %s", strerror(errno)));
+			continue;
+			}
+
+		if ( setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0 )
+			Error(fmt("can't set SO_REUSEADDR, %s", strerror(errno)));
+
+		// For IPv6 listening sockets, we don't want do dual binding to also
+		// get IPv4-mapped addresses because that's not as portable. e.g.
+		// many BSDs don't allow that.
+		if ( res->ai_family == AF_INET6 &&
+		     setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)) < 0 )
+			Error(fmt("can't set IPV6_V6ONLY, %s", strerror(errno)));
+
+		if ( bind(fd, res->ai_addr, res->ai_addrlen) < 0 )
+			{
+			Error(fmt("can't bind to %s:%s, %s", a.AsURIString().c_str(),
+			          port_str, strerror(errno)));
+			close(fd);
+
+			if ( errno == EADDRINUSE )
+				{
+				// Abandon completely this attempt to set up listening sockets,
+				// try again later.
+				CloseListenFDs();
+				listen_next_try = time(0) + bind_retry_interval;
+				return false;
+				}
+			continue;
+			}
+
+		if ( listen(fd, 50) < 0 )
+			{
+			Error(fmt("can't listen on %s:%s, %s", a.AsURIString().c_str(),
+			          port_str, strerror(errno)));
+			close(fd);
+			continue;
+			}
+
+		listen_fds.push_back(fd);
+		Log(fmt("listening on %s:%s (%s)", a.AsURIString().c_str(), port_str,
+		        listen_ssl ? "ssl" : "clear"));
 		}
 
-	if ( listen(*listen_fd, 50) < 0 )
-		{
-		Error(fmt("can't listen, %s", strerror(errno)));
-		return false;
-		}
+	freeaddrinfo(res0);
 
 	listen_next_try = 0;
-	Log(fmt("listening on %s:%d (%s)",
-		ip2a(ip), port, expect_ssl ? "ssl" : "clear"));
-	return true;
+	return listen_fds.size() > 0;
 	}
 
 bool SocketComm::AcceptConnection(int fd)
 	{
-	sockaddr_in client;
+	sockaddr_storage client;
 	socklen_t len = sizeof(client);
 
 	int clientfd = accept(fd, (sockaddr*) &client, &len);
 	if ( clientfd < 0 )
 		{
-		Error(fmt("accept failed, %s %d",
-				strerror(errno), errno));
+		Error(fmt("accept failed, %s %d", strerror(errno), errno));
+		return false;
+		}
+
+	if ( client.ss_family != AF_INET && client.ss_family != AF_INET6 )
+		{
+		Error(fmt("accept fail, unknown address family %d", client.ss_family));
+		close(clientfd);
 		return false;
 		}
 
 	Peer* peer = new Peer;
 	peer->id = id_counter++;
-	peer->ip = ntohl(client.sin_addr.s_addr);
-	peer->port = ntohs(client.sin_port);
+	peer->ip = client.ss_family == AF_INET ?
+	           IPAddr(((sockaddr_in*)&client)->sin_addr) :
+	           IPAddr(((sockaddr_in6*)&client)->sin6_addr);
+	peer->port = client.ss_family == AF_INET ?
+	             ntohs(((sockaddr_in*)&client)->sin_port) :
+	             ntohs(((sockaddr_in6*)&client)->sin6_port);
 	peer->connected = true;
-	peer->ssl = (fd == listen_fd_ssl);
+	peer->ssl = listen_ssl;
 	peer->compressor = false;
 
 	if ( peer->ssl )
@@ -4090,8 +4147,7 @@ bool SocketComm::AcceptConnection(int fd)
 
 	if ( ! peer->io->Init() )
 		{
-		Error(fmt("can't init peer io: %s",
-				  peer->io->Error()), false);
+		Error(fmt("can't init peer io: %s", peer->io->Error()), false);
 		return false;
 		}
 
@@ -4099,7 +4155,11 @@ bool SocketComm::AcceptConnection(int fd)
 
 	Log(fmt("accepted %s connection", peer->ssl ? "SSL" : "clear"), peer);
 
-	if ( ! SendToParent(MSG_CONNECTED, peer, 2, peer->ip, peer->port) )
+	uint32 bytes[4];
+	peer->ip.CopyIPv6(bytes, IPAddr::Host);
+
+	if ( ! SendToParent(MSG_CONNECTED, peer, 5, bytes[0], bytes[1], bytes[2],
+	                    bytes[3], peer->port) )
 		return false;
 
 	return true;
@@ -4117,12 +4177,19 @@ const char* SocketComm::MakeLogString(const char* msg, Peer* peer)
 
 	if ( peer )
 		len = snprintf(buffer, BUFSIZE, "[#%d/%s:%d] ", int(peer->id),
-				ip2a(peer->ip), peer->port);
+		               peer->ip.AsURIString().c_str(), peer->port);
 
 	len += safe_snprintf(buffer + len, BUFSIZE - len, "%s", msg);
 	return buffer;
 	}
 
+void SocketComm::CloseListenFDs()
+	{
+	for ( size_t i = 0; i < listen_fds.size(); ++i )
+		close(listen_fds[i]);
+	listen_fds.clear();
+	}
+
 void SocketComm::Error(const char* msg, bool kill_me)
 	{
 	if ( kill_me )
@@ -4165,7 +4232,7 @@ void SocketComm::Log(const char* msg, Peer* peer)
 
 void SocketComm::InternalError(const char* msg)
 	{
-	fprintf(stderr, "interal error in child: %s\n", msg);
+	fprintf(stderr, "internal error in child: %s\n", msg);
 	Kill();
 	}
 
@@ -4180,8 +4247,7 @@ void SocketComm::Kill()
 	LogProf();
 	Log("terminating");
 
-	close(listen_fd_clear);
-	close(listen_fd_ssl);
+	CloseListenFDs();
 
 	kill(getpid(), SIGTERM);
 
diff --git a/src/RemoteSerializer.h b/src/RemoteSerializer.h
index 05d25ca525..f6f94f53d3 100644
--- a/src/RemoteSerializer.h
+++ b/src/RemoteSerializer.h
@@ -10,8 +10,7 @@
 #include "Stats.h"
 #include "File.h"
 
-// All IP arguments are in host byte-order.
-// FIXME: Change this to network byte order
+#include <vector>
 
 class IncrementalSendTimer;
 
@@ -63,7 +62,8 @@ public:
 	bool CompleteHandshake(PeerID peer);
 
 	// Start to listen.
-	bool Listen(const IPAddr& ip, uint16 port, bool expect_ssl);
+	bool Listen(const IPAddr& ip, uint16 port, bool expect_ssl, bool ipv6,
+	            double retry);
 
 	// Stop it.
 	bool StopListening();
@@ -179,9 +179,7 @@ protected:
 	struct Peer {
 		PeerID id; // Unique ID (non-zero) per peer.
 
-		// ### Fix: currently, we only work for IPv4.
-		// addr_type ip;
-		uint32 ip;
+		IPAddr ip;
 
 		uint16 port;
 		handler_list handlers;
@@ -277,7 +275,7 @@ protected:
 	bool ProcessLogWrite();
 	bool ProcessRequestLogs();
 
-	Peer* AddPeer(uint32 ip, uint16 port, PeerID id = PEER_NONE);
+	Peer* AddPeer(const IPAddr& ip, uint16 port, PeerID id = PEER_NONE);
 	Peer* LookupPeer(PeerID id, bool only_if_connected);
 	void RemovePeer(Peer* peer);
 	bool IsConnectedPeer(PeerID id);
@@ -412,7 +410,6 @@ protected:
 			{
 			id = 0;
 			io = 0;
-			ip = 0;
 			port = 0;
 			state = 0;
 			connected = false;
@@ -424,7 +421,7 @@ protected:
 
 		RemoteSerializer::PeerID id;
 		ChunkedIO* io;
-		uint32 ip;
+		IPAddr ip;
 		uint16 port;
 		char state;
 		bool connected;
@@ -437,7 +434,7 @@ protected:
 		bool compressor;
 	};
 
-	bool Listen(uint32 ip, uint16 port, bool expect_ssl);
+	bool Listen();
 	bool AcceptConnection(int listen_fd);
 	bool Connect(Peer* peer);
 	bool CloseConnection(Peer* peer, bool reconnect);
@@ -482,6 +479,9 @@ protected:
 	bool ForwardChunkToPeer();
 	const char* MakeLogString(const char* msg, Peer *peer);
 
+	// Closes all file descriptors associated with listening sockets.
+	void CloseListenFDs();
+
 	// Peers we are communicating with:
 	declare(PList, Peer);
 	typedef PList(Peer) peer_list;
@@ -498,14 +498,15 @@ protected:
 	char parent_msgtype;
 	ChunkedIO::Chunk* parent_args;
 
-	int listen_fd_clear;
-	int listen_fd_ssl;
+	vector<int> listen_fds;
 
 	// If the port we're trying to bind to is already in use, we will retry
 	// it regularly.
-	uint32 listen_if;	// Fix: only supports IPv4
+	IPAddr listen_if;
 	uint16 listen_port;
 	bool listen_ssl;
+	bool enable_ipv6; // allow IPv6 listen sockets
+	uint32 bind_retry_interval;
 	time_t listen_next_try;
 	bool shutting_conns_down;
 	bool terminating;
diff --git a/src/bro.bif b/src/bro.bif
index 15740a83c7..3f4215dc13 100644
--- a/src/bro.bif
+++ b/src/bro.bif
@@ -5402,12 +5402,17 @@ function set_compression_level%(p: event_peer, level: count%) : bool
 ##
 ## ssl: If true, Bro uses SSL to encrypt the session.
 ##
+## ipv6: If true, enable listening on IPv6 addresses.
+##
+## retry_interval: If address *ip* is found to be already in use, this is
+##                 the interval at which to automatically retry binding.
+##
 ## Returns: True on success.
 ##
 ## .. bro:see:: connect disconnect
-function listen%(ip: addr, p: port, ssl: bool %) : bool
+function listen%(ip: addr, p: port, ssl: bool, ipv6: bool, retry_interval: interval%) : bool
 	%{
-	return new Val(remote_serializer->Listen(ip->AsAddr(), p->Port(), ssl), TYPE_BOOL);
+	return new Val(remote_serializer->Listen(ip->AsAddr(), p->Port(), ssl, ipv6, retry_interval), TYPE_BOOL);
 	%}
 
 ## Checks whether the last raised event came from a remote peer.
diff --git a/testing/btest/Baseline/istate.bro-ipv6/recv..stdout b/testing/btest/Baseline/istate.bro-ipv6/recv..stdout
new file mode 100644
index 0000000000..673af68234
--- /dev/null
+++ b/testing/btest/Baseline/istate.bro-ipv6/recv..stdout
@@ -0,0 +1 @@
+handshake done with peer: ::1
diff --git a/testing/btest/Baseline/istate.bro-ipv6/send..stdout b/testing/btest/Baseline/istate.bro-ipv6/send..stdout
new file mode 100644
index 0000000000..fbc855464d
--- /dev/null
+++ b/testing/btest/Baseline/istate.bro-ipv6/send..stdout
@@ -0,0 +1,2 @@
+handshake done with peer: ::1
+my_event: hello world
diff --git a/testing/btest/Baseline/istate.events-ssl/events.rec.log b/testing/btest/Baseline/istate.events-ssl/events.rec.log
new file mode 100644
index 0000000000..04993fb84a
--- /dev/null
+++ b/testing/btest/Baseline/istate.events-ssl/events.rec.log
@@ -0,0 +1,33 @@
+http_request
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_end_entity
+http_message_done
+http_signature_found
+http_reply
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_end_entity
+http_message_done
diff --git a/testing/btest/Baseline/istate.events-ssl/events.snd.log b/testing/btest/Baseline/istate.events-ssl/events.snd.log
new file mode 100644
index 0000000000..04993fb84a
--- /dev/null
+++ b/testing/btest/Baseline/istate.events-ssl/events.snd.log
@@ -0,0 +1,33 @@
+http_request
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_end_entity
+http_message_done
+http_signature_found
+http_reply
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_end_entity
+http_message_done
diff --git a/testing/btest/Baseline/istate.events-ssl/receiver.http.log b/testing/btest/Baseline/istate.events-ssl/receiver.http.log
index 1601f8ad3c..5a7912d23d 100644
--- a/testing/btest/Baseline/istate.events-ssl/receiver.http.log
+++ b/testing/btest/Baseline/istate.events-ssl/receiver.http.log
@@ -5,4 +5,4 @@
 #path	http
 #fields	ts	uid	id.orig_h	id.orig_p	id.resp_h	id.resp_p	trans_depth	method	host	uri	referrer	user_agent	request_body_len	response_body_len	status_code	status_msg	info_code	info_msg	filename	tags	username	password	proxied	mime_type	md5	extraction_file
 #types	time	string	addr	port	addr	port	count	string	string	string	string	string	count	count	count	string	count	string	string	table[enum]	string	string	table[string]	string	string	file
-1324314406.995958	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
+1336588614.060989	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
diff --git a/testing/btest/Baseline/istate.events-ssl/sender.http.log b/testing/btest/Baseline/istate.events-ssl/sender.http.log
index 1601f8ad3c..5a7912d23d 100644
--- a/testing/btest/Baseline/istate.events-ssl/sender.http.log
+++ b/testing/btest/Baseline/istate.events-ssl/sender.http.log
@@ -5,4 +5,4 @@
 #path	http
 #fields	ts	uid	id.orig_h	id.orig_p	id.resp_h	id.resp_p	trans_depth	method	host	uri	referrer	user_agent	request_body_len	response_body_len	status_code	status_msg	info_code	info_msg	filename	tags	username	password	proxied	mime_type	md5	extraction_file
 #types	time	string	addr	port	addr	port	count	string	string	string	string	string	count	count	count	string	count	string	string	table[enum]	string	string	table[string]	string	string	file
-1324314406.995958	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
+1336588614.060989	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
diff --git a/testing/btest/Baseline/istate.events/events.rec.log b/testing/btest/Baseline/istate.events/events.rec.log
new file mode 100644
index 0000000000..04993fb84a
--- /dev/null
+++ b/testing/btest/Baseline/istate.events/events.rec.log
@@ -0,0 +1,33 @@
+http_request
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_end_entity
+http_message_done
+http_signature_found
+http_reply
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_end_entity
+http_message_done
diff --git a/testing/btest/Baseline/istate.events/events.snd.log b/testing/btest/Baseline/istate.events/events.snd.log
new file mode 100644
index 0000000000..04993fb84a
--- /dev/null
+++ b/testing/btest/Baseline/istate.events/events.snd.log
@@ -0,0 +1,33 @@
+http_request
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_end_entity
+http_message_done
+http_signature_found
+http_reply
+http_begin_entity
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_header
+http_all_headers
+http_content_type
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_entity_data
+http_end_entity
+http_message_done
diff --git a/testing/btest/Baseline/istate.events/receiver.http.log b/testing/btest/Baseline/istate.events/receiver.http.log
index 25a7f289c0..55a0189cec 100644
--- a/testing/btest/Baseline/istate.events/receiver.http.log
+++ b/testing/btest/Baseline/istate.events/receiver.http.log
@@ -5,4 +5,4 @@
 #path	http
 #fields	ts	uid	id.orig_h	id.orig_p	id.resp_h	id.resp_p	trans_depth	method	host	uri	referrer	user_agent	request_body_len	response_body_len	status_code	status_msg	info_code	info_msg	filename	tags	username	password	proxied	mime_type	md5	extraction_file
 #types	time	string	addr	port	addr	port	count	string	string	string	string	string	count	count	count	string	count	string	string	table[enum]	string	string	table[string]	string	string	file
-1324314415.616486	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
+1336587178.164598	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
diff --git a/testing/btest/Baseline/istate.events/sender.http.log b/testing/btest/Baseline/istate.events/sender.http.log
index 25a7f289c0..55a0189cec 100644
--- a/testing/btest/Baseline/istate.events/sender.http.log
+++ b/testing/btest/Baseline/istate.events/sender.http.log
@@ -5,4 +5,4 @@
 #path	http
 #fields	ts	uid	id.orig_h	id.orig_p	id.resp_h	id.resp_p	trans_depth	method	host	uri	referrer	user_agent	request_body_len	response_body_len	status_code	status_msg	info_code	info_msg	filename	tags	username	password	proxied	mime_type	md5	extraction_file
 #types	time	string	addr	port	addr	port	count	string	string	string	string	string	count	count	count	string	count	string	string	table[enum]	string	string	table[string]	string	string	file
-1324314415.616486	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
+1336587178.164598	arKYeMETxOg	141.42.64.125	56730	125.190.109.199	80	1	GET	www.icir.org	/	-	Wget/1.10	0	9130	200	OK	-	-	-	(empty)	-	-	-	text/html	-	-
diff --git a/testing/btest/istate/bro-ipv6.bro b/testing/btest/istate/bro-ipv6.bro
new file mode 100644
index 0000000000..6230018636
--- /dev/null
+++ b/testing/btest/istate/bro-ipv6.bro
@@ -0,0 +1,52 @@
+# @TEST-GROUP: comm
+#
+# @TEST-REQUIRES: ifconfig | grep -q "inet6 ::1"
+#
+# @TEST-EXEC: btest-bg-run recv bro -b ../recv.bro
+# @TEST-EXEC: btest-bg-run send bro -b ../send.bro
+# @TEST-EXEC: btest-bg-wait -k 20
+# 
+# @TEST-EXEC: btest-diff recv/.stdout
+# @TEST-EXEC: btest-diff send/.stdout
+
+@TEST-START-FILE send.bro
+
+@load base/frameworks/communication
+
+redef Communication::nodes += {
+    ["foo"] = [$host=[::1], $connect=T, $events=/my_event/]
+};
+
+global my_event: event(s: string);
+
+event remote_connection_handshake_done(p: event_peer)
+	{
+	print fmt("handshake done with peer: %s", p$host);
+	}
+
+event my_event(s: string)
+	{
+	print fmt("my_event: %s", s);
+	terminate();
+	}
+
+@TEST-END-FILE
+
+#############
+
+@TEST-START-FILE recv.bro
+
+@load frameworks/communication/listen
+
+redef Communication::listen_ipv6=T;
+
+global my_event: event(s: string);
+
+event remote_connection_handshake_done(p: event_peer)
+	{
+	print fmt("handshake done with peer: %s", p$host);
+	event my_event("hello world");
+	terminate();
+	}
+
+@TEST-END-FILE
diff --git a/testing/btest/istate/events-ssl.bro b/testing/btest/istate/events-ssl.bro
index 25aa2dc8fb..c86087df81 100644
--- a/testing/btest/istate/events-ssl.bro
+++ b/testing/btest/istate/events-ssl.bro
@@ -8,8 +8,10 @@
 # @TEST-EXEC: btest-diff receiver/http.log
 # @TEST-EXEC: cmp sender/http.log receiver/http.log
 # 
-# @TEST-EXEC: bro -x sender/events.bst http/base   | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.snd.log
-# @TEST-EXEC: bro -x receiver/events.bst http/base | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.rec.log
+# @TEST-EXEC: bro -x sender/events.bst | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.snd.log
+# @TEST-EXEC: bro -x receiver/events.bst | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.rec.log
+# @TEST-EXEC: btest-diff events.rec.log
+# @TEST-EXEC: btest-diff events.snd.log
 # @TEST-EXEC: cmp events.rec.log events.snd.log
 # 
 # We don't compare the transmitted event paramerters anymore. With the dynamic
diff --git a/testing/btest/istate/events.bro b/testing/btest/istate/events.bro
index 81a1d765db..6d8227c810 100644
--- a/testing/btest/istate/events.bro
+++ b/testing/btest/istate/events.bro
@@ -10,6 +10,8 @@
 # 
 # @TEST-EXEC: bro -x sender/events.bst | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.snd.log
 # @TEST-EXEC: bro -x receiver/events.bst | sed 's/^Event \[[-0-9.]*\] //g' | grep '^http_' | grep -v http_stats | sed 's/(.*$//g'  >events.rec.log
+# @TEST-EXEC: btest-diff events.rec.log
+# @TEST-EXEC: btest-diff events.snd.log
 # @TEST-EXEC: cmp events.rec.log events.snd.log
 # 
 # We don't compare the transmitted event paramerters anymore. With the dynamic