diff --git a/Makefile b/Makefile
index 2b1d09d..21d7b73 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@
 # warning: do not set -O to 2, see TODO
 CFLAGS = -Wall -Wextra -Werror -O1 -g
 LDFLAGS=
-OBJS   = client.o net.o udpxd.o
+OBJS   = host.o client.o net.o udpxd.o
 DST    = udpxd
 PREFIX = /usr/local
 UID    = root
diff --git a/client.c b/client.c
index 86d34f2..fa2e24b 100644
--- a/client.c
+++ b/client.c
@@ -35,10 +35,10 @@ client_t *client_find_fd(int fd) {
   return client; /*  maybe NULL! */
 }
 
-client_t *client_find_src(struct sockaddr_in *src) {
+client_t *client_find_src(host_t *src) {
   client_t *current = NULL;
   client_iter(clients, current) {
-    if (current->src == src)
+    if(strcmp(current->src->ip, src->ip) == 0 && current->src->port == src->port)
       return current;
   }
   return NULL;
@@ -48,7 +48,7 @@ void client_seen(client_t *client) {
   client->lastseen = (long)time(0);
 }
 
-client_t *client_new(int fd, struct sockaddr_in *src, struct sockaddr_in *dst) {
+client_t *client_new(int fd, host_t *src, host_t *dst) {
   client_t *client = malloc(sizeof(client_t));
   client->socket = fd;
   client->src = src;
@@ -73,10 +73,8 @@ void client_clean() {
     diff = now - current->lastseen;
     if(diff >= MAXAGE) {
       if(VERBOSE) {
-	char *srcip  = inet_ntoa(current->src->sin_addr);
-	char *bindip = inet_ntoa(current->dst->sin_addr);
 	fprintf(stderr, "closing socket %s:%d for client %s:%d (aged out after %d seconds)\n",
-		srcip, ntohs(current->src->sin_port), bindip, ntohs(current->dst->sin_port), MAXAGE);
+		current->src->ip, current->src->port, current->dst->ip, current->dst->port, MAXAGE);
       }
       client_close(current);
     }
diff --git a/client.h b/client.h
index 4848f2b..105a439 100644
--- a/client.h
+++ b/client.h
@@ -39,14 +39,16 @@ typedef uint8_t byte;
 #endif
 
 #include "uthash.h"
+#include "host.h"
 
 #define MAXAGE         3600 /* seconds after which to close outgoing sockets and forget client src */
 
 struct _client_t {
   int socket;               /* bind socket for outgoing traffic */
-  struct sockaddr_in *src;  /* client src (ip+port) from incoming socket */
-  struct sockaddr_in *dst;  /* client dst (ip+port) to outgoing socket */
+  host_t *src;              /* client src (ip+port) from incoming socket */
+  host_t *dst;              /* client dst (ip+port) to outgoing socket */
   uint64_t lastseen;        /* when did we recv last time from it */
+  size_t size;              /* sockaddr size */
   UT_hash_handle hh;
 };
 typedef struct _client_t client_t;
@@ -78,8 +80,8 @@ void client_close(client_t *client);
 void client_clean();
 
 client_t *client_find_fd(int fd);
-client_t *client_find_src(struct sockaddr_in *src);
-client_t *client_new(int fd, struct sockaddr_in *src, struct sockaddr_in *dst);
+client_t *client_find_src(host_t *src);
+client_t *client_new(int fd, host_t *src, host_t *dst);
 
 
 #endif
diff --git a/net.c b/net.c
index 32df7ba..a5b8bea 100644
--- a/net.c
+++ b/net.c
@@ -21,6 +21,8 @@
 
 #include "net.h"
 #include "client.h"
+#include "host.h"
+
 
 
 char *ntoa(struct sockaddr_in *src) {
@@ -29,6 +31,7 @@ char *ntoa(struct sockaddr_in *src) {
   return ip;
 }
 
+
 /* called each time when the loop restarts to feed select() correctly */
 int fill_set(fd_set *fds) {
   int max = 0;
@@ -58,57 +61,106 @@ int get_sender(fd_set *fds) {
     return i;
 }
 
+
 /* bind to a socket, either for listen() or for outgoing src ip binding */
-int bindsocket( char* ip, int port ) {
+int bindsocket( host_t *sock_h) {
   int fd;
-  struct sockaddr_in addr;
+  int err = 0;
 
-  addr.sin_family = AF_INET;
-  addr.sin_addr.s_addr = inet_addr( ip );
-  addr.sin_port = htons( port );
+  if(sock_h->is_v6) {
+    fd = socket( PF_INET6, SOCK_DGRAM, IPPROTO_UDP );
+  }
+  else {
+    fd = socket( PF_INET, SOCK_DGRAM, IPPROTO_UDP );
+  }
 
-  fd = socket( PF_INET, SOCK_DGRAM, IPPROTO_IP );
-  if( -1 == bind( fd, (struct sockaddr*)&addr, sizeof( addr ) ) ) {
-    fprintf( stderr, "Cannot bind address (%s:%d)\n", ip, port );
-    exit( 1 );
+  if( -1 == bind( fd, (struct sockaddr*)sock_h->sock, sock_h->size ) ) {
+    err = 1;
+  }
+
+  if(err) {
+    fprintf( stderr, "Cannot bind address ([%s]:%d)\n", sock_h->ip, sock_h->port );
+    perror(NULL);
+    return -1;
   }
   
   return fd;
 }
 
-/* handle new or known incoming requests */
-void handle_inside(int inside, char *bindip, struct sockaddr_in *dst) {
-  int len;
-  unsigned char buffer[MAX_BUFFER_SIZE];
-  struct sockaddr_in *src;
-  client_t *client;
-  int output;
-  char *srcip;
-  char *dstip = ntoa(dst);
-  size_t size = sizeof(struct sockaddr_in);
-  src = malloc(size);
-  
-  len = recvfrom( inside, buffer, sizeof( buffer ), 0, (struct sockaddr*)src, (socklen_t *)&size );
-  srcip = ntoa(src);
+int start_listener (char *inip, char *inpt, char *srcip, char *dstip, char *dstpt) {
+  host_t *listen_h = get_host(inip, atoi(inpt), NULL, NULL);
+  host_t *dst_h    = get_host(dstip, atoi(dstpt), NULL, NULL);
+  host_t *bind_h   = NULL;
+
+  if(srcip != NULL) {
+    bind_h   = get_host(srcip, 0, NULL, NULL);
+  }
+  else {
+    if(dst_h->is_v6)
+      bind_h = get_host("::0", 0, NULL, NULL);
+    else
+      bind_h = get_host("0.0.0.0", 0, NULL, NULL);
+  }
+
+  int listen = bindsocket(listen_h);
+
+  if(listen == -1)
+    return 1;
+
+  if(VERBOSE) {
+    fprintf(stderr, "Listening on %s:%s, forwarding to %s:%s",
+	    inip, inpt, dstip, dstpt);
+    if(srcip != NULL)
+      fprintf(stderr, ", binding to %s\n", srcip);
+    else
+      fprintf(stderr, "\n");
+  }
+  
+  main_loop(listen, listen_h, bind_h, dst_h);
+
+  return 0;
+}
+
+/* handle new or known incoming requests
+   FIXME: check client handling:
+   http://long.ccaba.upc.es/long/045Guidelines/eva/ipv6.html#daytimeServer6
+*/
+void handle_inside(int inside, host_t *listen_h, host_t *bind_h, host_t *dst_h) {
+  int len;
+  unsigned char buffer[MAX_BUFFER_SIZE];
+  void *src;
+  client_t *client;
+  host_t *src_h;
+  int output;
+  size_t size = listen_h->size;
+
+  src = malloc(size);
+  
+  len = recvfrom( inside, buffer, sizeof( buffer ), 0,
+		  (struct sockaddr*)src, (socklen_t *)&size );
+
+  if(listen_h->is_v6)
+    src_h = get_host(NULL, 0, NULL, (struct sockaddr_in6 *)src);
+  else
+    src_h = get_host(NULL, 0, (struct sockaddr_in *)src, NULL);
 
   if(VERBOSE) {
-    char *srcip = ntoa(src);
     fprintf(stderr, "New incomming request from %s:%d with %d bytes\n",
-	    srcip, ntohs(src->sin_port), len);
+	    src_h->ip, src_h->port, len);
   }
 
   if(len > 0) {
     /* do we know it ? */
-    client = client_find_src(src);
+    client = client_find_src(src_h);
     if(client != NULL) {
       /* yes, we know it, send req out via existing bind socket */
       if(VERBOSE) {
 	fprintf(stderr, "Client %s:%d is known, forwarding data to %s:%d\n",
-		srcip, ntohs(src->sin_port), dstip, ntohs(dst->sin_port));
-  
+		src_h->ip, src_h->port, dst_h->ip, dst_h->port);
+	
       }
-      if(sendto(client->socket, buffer, len, 0, (struct sockaddr*)dst, size) < 0) {
-	fprintf(stderr, "unable to forward to %s:%d\n", dstip, ntohs(dst->sin_port));
+      if(sendto(client->socket, buffer, len, 0, (struct sockaddr*)dst_h->sock, dst_h->size) < 0) {
+	fprintf(stderr, "unable to forward to %s:%d\n", dst_h->ip, dst_h->port);
 	perror(NULL);
       }
       else {
@@ -119,29 +171,38 @@ void handle_inside(int inside, char *bindip, struct sockaddr_in *dst) {
       /* unknown client, open new out socket */
       if(VERBOSE) {
 	fprintf(stderr, "Client %s:%d is unknown, forwarding data to %s:%d ",
-		srcip, ntohs(src->sin_port), dstip, ntohs(dst->sin_port));
+		src_h->ip, src_h->port, dst_h->ip, dst_h->port);
   
       }
 
-      if(bindip == NULL)
-	output = bindsocket("0.0.0.0", 0);
-      else
-	output = bindsocket(bindip, 0);
+      output = bindsocket(bind_h);
       
       /* send req out */
-      if(sendto(output, buffer, len, 0, (struct sockaddr*)dst, size) < 0) {
-	fprintf(stderr, "unable to forward to %s:%d\n", dstip, ntohs(dst->sin_port));
+      if(sendto(output, buffer, len, 0, (struct sockaddr*)dst_h->sock, dst_h->size) < 0) {
+	fprintf(stderr, "unable to forward to %s:%d\n", dst_h->ip, dst_h->port);
 	perror(NULL);
       }
       else {
-	struct sockaddr_in *ret = malloc(size);
-	getsockname(output, (struct sockaddr*)ret, (socklen_t *)&size);
-	client = client_new(output, src, ret);
+	size = listen_h->size;
+	host_t *ret_h;
+	if(listen_h->is_v6) {
+	  struct sockaddr_in6 *ret = malloc(size);
+	  getsockname(output, (struct sockaddr*)ret, (socklen_t *)&size);
+	  ret_h = get_host(NULL, 0, NULL, ret);
+	  client = client_new(output, src_h, ret_h);
+	}
+	else {
+	  struct sockaddr_in *ret = malloc(size);	  
+	  getsockname(output, (struct sockaddr*)ret, (socklen_t *)&size);
+	  ret_h = get_host(NULL, 0, ret, NULL);
+	  client = client_new(output, src_h, ret_h);
+	}
+
 	client_add(client);
+
 	if(VERBOSE) {
-	  if(bindip != NULL) {
-	    char *bindip = ntoa(ret);
-	    fprintf(stderr, "from %s:%d\n", bindip, ntohs(ret->sin_port));
+	  if(strcmp(bind_h->ip, "0.0.0.0") != 0 || strcmp(bind_h->ip, "::0") != 0) {
+	    fprintf(stderr, "from %s:%d\n", ret_h->ip, ret_h->port);
 	  }
 	  else {
 	    fprintf(stderr, "\n");
@@ -151,18 +212,17 @@ void handle_inside(int inside, char *bindip, struct sockaddr_in *dst) {
     }
   }
 
-  free(dstip);
-  free(srcip);
+  /* FIXME: free? */
 }
 
 /* handle answer from the outside */
-void handle_outside(int inside, int outside) {
+void handle_outside(int inside, int outside, host_t *outside_h) {
   int len;
   unsigned char buffer[MAX_BUFFER_SIZE];
-  struct sockaddr_in *src;
+  void *src;
   client_t *client;
 
-  size_t size = sizeof(struct sockaddr_in);
+  size_t size = outside_h->size;
   src = malloc(size);
   
   len = recvfrom( outside, buffer, sizeof( buffer ), 0, (struct sockaddr*)src, (socklen_t *)&size );
@@ -172,7 +232,7 @@ void handle_outside(int inside, int outside) {
     client = client_find_fd(outside);
     if(client != NULL) {
       /* yes, we know it */
-      if(sendto(inside, buffer, len, 0, (struct sockaddr*)client->src, size) < 0) {
+      if(sendto(inside, buffer, len, 0, (struct sockaddr*)client->src, client->size) < 0) {
 	perror("unable to send back to client"); /* FIXME: add src+port */
 	client_close(client);
       }
@@ -180,3 +240,33 @@ void handle_outside(int inside, int outside) {
   }
 }
 
+/* runs forever, handles incoming requests on the inside and answers on the outside */
+int main_loop(int listensocket, host_t *listen_h, host_t *bind_h, host_t *dst_h) {
+    int max, sender;
+    fd_set fds;
+
+    for(;;) {
+      FD_ZERO(&fds);
+      max = fill_set(&fds);
+
+      FD_SET(listensocket, &fds);
+      if (listensocket > max)
+	max = listensocket;
+
+      select(max + 1, &fds, NULL, NULL, NULL);
+
+      if (FD_ISSET(listensocket, &fds)) {
+	/* incoming client on the inside, get src, bind output fd, add to list
+	   if known, otherwise just handle it  */
+	handle_inside(listensocket, listen_h, bind_h, dst_h);
+      }
+      else {
+	/* remote answer came in on an output fd, proxy back to the inside */
+	sender = get_sender(&fds);
+	handle_outside(listensocket, sender, dst_h);
+      }
+
+      /* close old outputs, if any */
+      client_clean();
+    }
+}
diff --git a/net.h b/net.h
index e0caca1..d23e117 100644
--- a/net.h
+++ b/net.h
@@ -35,6 +35,7 @@
 #include <sys/fcntl.h>
 #include <arpa/inet.h>
 
+
 #include "client.h"
 
 #define MAX_BUFFER_SIZE 65535
@@ -42,10 +43,20 @@
 extern client_t *clients;
 extern int VERBOSE;
 
+
+
+void handle_inside(int inside, host_t *listen_h, host_t *bind_h, host_t *dst_h);
+void handle_outside(int inside, int outside, host_t *outside_h);
+
+int main_loop(int listensocket, host_t *listen_h, host_t *bind_h, host_t *dst_h);
+int start_listener (char *inip, char *inpt, char *srcip, char *dstip, char *dstpt);
+
 int fill_set(fd_set *fds);
 int get_sender(fd_set *fds);
-int bindsocket( char* ip, int port );
-void handle_inside(int inside, char *bindip, struct sockaddr_in *dst);
-void handle_outside(int inside, int outside);
+int bindsocket( host_t *sock_h);
+
+
+
+#define _IS_LINK_LOCAL(a) do { IN6_IS_ADDR_LINKLOCAL(a); } while(0)
 
 #endif
diff --git a/udpxd.c b/udpxd.c
index 2f32192..26780fa 100644
--- a/udpxd.c
+++ b/udpxd.c
@@ -27,43 +27,70 @@
 client_t *clients = NULL;
 int VERBOSE = 0;
 
-/* runs forever, handles incoming requests on the inside and answers on the outside */
-int main_loop(int listensocket, char *bindip, struct sockaddr_in *dst) {
-    int max, sender;
-    fd_set fds;
+/* parse ip:port */
+int parse_ip(char *src, char *ip, char *pt) {
+  char *ptr = NULL;
 
-    for(;;) {
-      FD_ZERO(&fds);
-      max = fill_set(&fds);
+  if (strchr(optarg, '[')) {
+    /* v6 */
+    ptr = strtok(&src[1], "]");
 
-      FD_SET(listensocket, &fds);
-      if (listensocket > max)
-	max = listensocket;
-
-      select(max + 1, &fds, NULL, NULL, NULL);
-
-      if (FD_ISSET(listensocket, &fds)) {
-	/* incoming client on the inside, get src, bind output fd, add to list
-	   if known, otherwise just handle it  */
-	handle_inside(listensocket, bindip, dst);
-      }
-      else {
-	/* remote answer came in on an output fd, proxy back to the inside */
-	sender = get_sender(&fds);
-	handle_outside(listensocket, sender);
-      }
-
-      /* close old outputs, if any */
-      client_clean();
+    if(strlen(ptr) > INET6_ADDRSTRLEN) {
+      fprintf(stderr, "ip v6 address is too long!\n");
+      return 1;
     }
+    
+    strncpy(ip, ptr, strlen(ptr)+1);
+    ptr = strtok(NULL, "]");
+    if(ptr)
+      ptr = &ptr[1]; /* remove : */
+  }
+  else if(strchr(optarg, ':')) {
+    /* v4 */
+    ptr = strtok(src, ":");
+    
+    if(strlen(ptr) > INET_ADDRSTRLEN) {
+      fprintf(stderr, "ip v4 address is too long!\n");
+      return 1;
+    }
+    
+    strncpy(ip, ptr, strlen(ptr)+1);
+    ptr = strtok(NULL, ":");
+  }
+  else {
+    fprintf(stderr, "Invalid ip/port specification!\n");
+    return 1;
+  }
+
+  if(ptr != NULL) {
+    /* got a port */
+    if(strlen(ptr) > 5) {
+      fprintf(stderr, "port is too long!\n");
+      return 1;
+    }
+    else {
+      if(atoi(ptr) > 65535) {
+	fprintf(stderr, "maximum port number possible: 65535!\n");
+	return 1;
+      }
+      strncpy(pt, ptr, strlen(ptr)+1);
+    }
+  }
+  else {
+    fprintf(stderr, "Port is missing!\n");
+    return 1;
+  }
+
+  return 0;
 }
 
 
+
+
 int main ( int argc, char* argv[] ) {
-  int listen, opt;
+  int opt, err;
   char *inip, *inpt, *srcip, *dstip, *dstpt;
-  struct sockaddr_in *dst;
-  char colon[] = ":";
+  err = 0;
   
   static struct option longopts[] = {
     { "listen",    required_argument, NULL,           'l' },
@@ -80,7 +107,7 @@ int main ( int argc, char* argv[] ) {
   }
 
   srcip = dstip = inip = dstpt = inpt = NULL;
-    
+  
   while ((opt = getopt_long(argc, argv, "l:b:d:vVh?", longopts, NULL)) != -1) {
     switch (opt) {
     case 'v':
@@ -96,49 +123,27 @@ int main ( int argc, char* argv[] ) {
       VERBOSE = 1;
       break;
     case 'l':
-      if(strchr(optarg, ':')) {
-	  char *ptr = NULL;
-	  ptr = strtok(optarg, colon);
-	  inip = malloc( strlen(ptr)+1);
-	  strncpy(inip, ptr, strlen(ptr)+1);
-	  ptr = strtok(NULL, colon);
-	  if(ptr != NULL) {
-	    inpt = malloc( strlen(ptr)+1);
-	    strncpy(inpt, ptr, strlen(ptr)+1);
-	  }
-	  else {
-	    fprintf(stderr, "Listen port for parameter -l is missing!\n");
-	    return 0;
-	  }
-      }
-      else {
+      inip  = malloc(INET6_ADDRSTRLEN+1);
+      inpt  = malloc(6);
+      if (parse_ip(optarg, inip, inpt) != 0) {
 	fprintf(stderr, "Parameter -l has the format <ip-address:port>!\n");
-	return 0;
+	err = 1;
       }
       break;
     case 'd':
-      if(strchr(optarg, ':')) {
-	  char *ptr = NULL;
-	  ptr = strtok(optarg, colon);
-	  dstip = malloc( strlen(ptr)+1);
-	  strncpy(dstip, ptr, strlen(ptr)+1);
-	  ptr = strtok(NULL, colon);
-	  if(ptr != NULL) {
-	    dstpt = malloc( strlen(ptr)+1);
-	    strncpy(dstpt, ptr, strlen(ptr)+1);
-	  }
-	  else {
-	    fprintf(stderr, "Destination port for parameter -d is missing!\n");
-	    return 0;
-	  }
-      }
-      else {
+      dstip = malloc(INET6_ADDRSTRLEN+1);
+      dstpt = malloc(6);
+      if (parse_ip(optarg, dstip, dstpt) != 0) {
 	fprintf(stderr, "Parameter -d has the format <ip-address:port>!\n");
-	return 0;
+	err = 1;
       }
       break;
     case 'b':
-      srcip = malloc(strlen(optarg));
+      if(strlen(optarg) > INET6_ADDRSTRLEN) {
+	fprintf(stderr, "Bind ip address is too long!\n");
+	err = 1;
+      }
+      srcip = malloc(INET6_ADDRSTRLEN+1);
       strncpy(srcip, optarg, strlen(optarg));
       break;
     default:
@@ -151,36 +156,33 @@ int main ( int argc, char* argv[] ) {
   if(inip == NULL) {
     fprintf(stderr, "-l parameter is required!\n");
     usage();
-    return 1;
+    err = 1;
   }
   
   if(dstip == NULL) {
     fprintf(stderr, "-d parameter is required!\n");
     usage();
-    return 1;
+    err = 1;
   }
 
-  listen = bindsocket(inip, atoi(inpt));
-
-  dst = malloc(sizeof(struct sockaddr_in));
-  dst->sin_family = AF_INET;
-  dst->sin_addr.s_addr = inet_addr( dstip );
-  dst->sin_port = htons( atoi( dstpt ) );
-
-  if(VERBOSE) {
-    fprintf(stderr, "Listening on %s:%s, forwarding to %s:%s",
-	    inip, inpt, dstip, dstpt);
-    if(srcip != NULL)
-      fprintf(stderr, ", binding to %s\n", srcip);
-    else
-      fprintf(stderr, "\n");
+  if(! err) {
+    err = start_listener (inip, inpt, srcip, dstip, dstpt);
   }
   
-  main_loop(listen, srcip, dst);
+  /* FIXME: add sighandler */
 
-  /* FIXME: add sighandler, clean up mem */
-  
-  return 0;
+  if(srcip != NULL)
+    free(srcip);
+  if(dstip != NULL)
+    free(dstip);
+  if(inip != NULL)
+    free(inip);
+  if(inpt != NULL)
+    free(inpt);
+  if(dstpt != NULL)
+    free(dstpt);
+
+  return err;
 }
 
 void usage() {
diff --git a/udpxd.h b/udpxd.h
index dbe4cf8..fd32f1b 100644
--- a/udpxd.h
+++ b/udpxd.h
@@ -41,5 +41,6 @@
 
 int main_loop(int listensocket, char *bindip, struct sockaddr_in *dst);
 void usage();
+int parse_ip(char *src, char *ip, char *pt);
 
 #endif