diff --git a/host.c b/host.c
new file mode 100644
index 0000000..b111381
--- /dev/null
+++ b/host.c
@@ -0,0 +1,132 @@
+/*
+    This file is part of udpxd.
+
+    Copyright (C) 2015 T.v.Dein.
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    You can contact me by mail: <tom AT vondein DOT org>.
+*/
+
+#include "host.h"
+
+/* fill a generic struct depending of what we already know,
+   which is easier to pass between functions,
+   maybe v4 or v6, filled from existing structs or from strings,
+   which create the sockaddr* structs */
+host_t *get_host(char *ip, int port, struct sockaddr_in *v4, struct sockaddr_in6 *v6) {
+  host_t *host = malloc(sizeof(host_t));
+  host->sock = NULL;
+  host->is_v6 = 0;
+  host->port = port;
+
+  if(ip != NULL) {
+    if(is_v6(ip)) {
+      struct sockaddr_in6 *tmp = malloc(sizeof(struct sockaddr_in6));
+      memset(tmp, 0, sizeof(struct sockaddr_in6));
+      
+      inet_pton(AF_INET6, ip, (struct in6_addr*)&tmp->sin6_addr);
+      
+      tmp->sin6_family = AF_INET6;
+      tmp->sin6_port = htons( port );
+ 
+      if (is_linklocal((struct in6_addr*)&tmp->sin6_addr))
+	tmp->sin6_scope_id = get_v6_scope(ip);
+      else
+	tmp->sin6_scope_id = 0;
+
+      host->is_v6 = 1;
+      host->sock  = (struct sockaddr*)tmp;
+      host->size = sizeof(struct sockaddr_in6);
+    }
+    else {
+      struct sockaddr_in *tmp = malloc(sizeof(struct sockaddr_in));
+      memset(tmp, 0, sizeof(struct sockaddr_in));
+      tmp->sin_family = AF_INET;
+      tmp->sin_addr.s_addr = inet_addr( ip );
+      tmp->sin_port = htons( port );
+      host->sock   = (struct sockaddr*)tmp;
+      host->size = sizeof(struct sockaddr_in);
+    }
+  }
+  else if(v4 != NULL) {
+    struct sockaddr_in *tmp = malloc(sizeof(struct sockaddr_in));
+    memcpy(tmp, v4, sizeof(struct sockaddr_in));
+    host->ip = malloc(INET_ADDRSTRLEN);
+    inet_ntop(AF_INET, (struct in_addr *)&tmp->sin_addr, host->ip, INET_ADDRSTRLEN);
+    host->port = ntohs(tmp->sin_port);
+    host->sock = (struct sockaddr*)tmp;
+    host->size = sizeof(struct sockaddr_in);
+  }
+  else if(v6 != NULL) {
+    struct sockaddr_in6 *tmp = malloc(sizeof(struct sockaddr_in6));
+    memcpy(tmp, v6, sizeof(struct sockaddr_in6));
+    host->ip = malloc(INET6_ADDRSTRLEN);
+    inet_ntop(AF_INET, (struct in6_addr *)&tmp->sin6_addr, host->ip, INET6_ADDRSTRLEN);
+    host->port = ntohs(tmp->sin6_port);
+    host->sock = (struct sockaddr*)tmp;
+    host->is_v6 = 1;
+    host->size = sizeof(struct sockaddr_in6);
+  }
+  else {
+    fprintf(stderr, "call invalid!\n");
+    exit(1); /* shall not happen */
+  }
+
+  return host;
+}
+
+char *is_v6(char *ip) {
+  return strchr(ip, ':');
+}
+
+/* via http://stackoverflow.com/questions/13504934/binding-sockets-to-ipv6-addresses
+   return the interface index (aka scope) of an ipv6 address, which is required
+   in order to bind to it.
+*/
+unsigned get_v6_scope(const char *ip){
+  struct ifaddrs *addrs, *addr;
+    char ipAddress[NI_MAXHOST];
+    uint32_t scope=0;
+    int i;
+    
+    // walk over the list of all interface addresses
+    getifaddrs(&addrs);
+    for(addr=addrs;addr;addr=addr->ifa_next){
+        if (addr->ifa_addr && addr->ifa_addr->sa_family==AF_INET6){ // only interested in ipv6 ones
+            getnameinfo(addr->ifa_addr,sizeof(struct sockaddr_in6),ipAddress,sizeof(ipAddress),NULL,0,NI_NUMERICHOST);
+            // result actually contains the interface name, so strip it
+            for(i=0;ipAddress[i];i++){
+                if(ipAddress[i]=='%'){
+                    ipAddress[i]='\0';
+                    break;
+                }
+            }
+            // if the ip matches, convert the interface name to a scope index
+            if(strcmp(ipAddress,ip)==0){
+                scope=if_nametoindex(addr->ifa_name);
+                break;
+            }
+        }
+    }
+    freeifaddrs(addrs);
+    fprintf(stderr, "scope: %d\n", scope);
+    return scope;
+}
+
+/* this is the contents of the makro IN6_IS_ADDR_LINKLOCAL,
+   which doesn't compile, when used directly, for whatever reasons */
+int is_linklocal(struct in6_addr *a) {
+  return ((a->s6_addr[0] == 0xfe) && ((a->s6_addr[1] & 0xc0) == 0x80));
+}
diff --git a/host.h b/host.h
new file mode 100644
index 0000000..0241f51
--- /dev/null
+++ b/host.h
@@ -0,0 +1,54 @@
+/*
+    This file is part of udpxd.
+
+    Copyright (C) 2015 T.v.Dein.
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    You can contact me by mail: <tom AT vondein DOT org>.
+*/
+
+#ifndef _HAVE_HOST_H
+#define _HAVE_HOST_H
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <netdb.h>
+#include <net/if.h> // if_nametoindex()
+#include <ifaddrs.h>
+
+struct _host_t {
+  int is_v6;
+  struct sockaddr *sock;
+  size_t size;
+  char *ip;
+  int port;
+};
+typedef struct _host_t host_t;
+
+unsigned get_v6_scope(const char *ip);
+int is_linklocal(struct in6_addr *a);
+host_t *get_host(char *ip, int port, struct sockaddr_in *v4, struct sockaddr_in6 *v6);
+char *is_v6(char *ip);
+
+#endif