diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index eb7f76f..d4b4322 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -199,7 +199,12 @@ or
 .B --listen-address
 configuration, indeed
 .B --auth-server
-will overide these and provide a different DNS service on the specified interface. The <domain> is the "glue record". It should resolve in the global DNS to a A and/or AAAA record which points to the address dnsmasq is listening on.
+will overide these and provide a different DNS service on the
+specified interface. The <domain> is the "glue record". It should
+resolve in the global DNS to a A and/or AAAA record which points to
+the address dnsmasq is listening on. When an interface is specified,
+it may be qualified with "/4" or "/6" to specify only the IPv4 or IPv6
+addresses associated with the interface.
 .TP 
 .B \-2, --no-dhcp-interface=<interface name>
 Do not provide DHCP or TFTP on the specified interface, but do provide DNS service.
diff --git a/src/auth.c b/src/auth.c
index e7168c2..763c169 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -660,16 +660,16 @@ size_t answer_auth(struct dns_header *header, char *limit, size_t qlen, time_t n
 		  *cut = 0;
 		
 		for (addrlist = intr->addr; addrlist; addrlist = addrlist->next) 
-		  if (!(subnet->flags & ADDRLIST_IPV6) &&
-		      (local_query || filter_zone(zone, F_IPV4,  &addrlist->addr)) && 
+		  if (!(addrlist->flags & ADDRLIST_IPV6) &&
+		      (local_query || filter_zone(zone, F_IPV4, &addrlist->addr)) && 
 		      add_resource_record(header, limit, &trunc, -axfroffset, &ansp, 
 					  daemon->auth_ttl, NULL, T_A, C_IN, "4", cut ? intr->name : NULL, &addrlist->addr))
 		    anscount++;
 		
 #ifdef HAVE_IPV6
 		for (addrlist = intr->addr; addrlist; addrlist = addrlist->next) 
-		  if ((subnet->flags & ADDRLIST_IPV6) && 
-		      (local_query || filter_zone(zone, F_IPV6,  &addrlist->addr)) &&
+		  if ((addrlist->flags & ADDRLIST_IPV6) && 
+		      (local_query || filter_zone(zone, F_IPV6, &addrlist->addr)) &&
 		      add_resource_record(header, limit, &trunc, -axfroffset, &ansp, 
 					  daemon->auth_ttl, NULL, T_AAAA, C_IN, "6", cut ? intr->name : NULL, &addrlist->addr))
 		    anscount++;
diff --git a/src/network.c b/src/network.c
index 3515a52..51d9d53 100644
--- a/src/network.c
+++ b/src/network.c
@@ -159,7 +159,8 @@ int iface_check(int family, struct all_addr *addr, char *name, int *auth)
   for (tmp = daemon->authinterface; tmp; tmp = tmp->next)
     if (tmp->name)
       {
-	if (strcmp(tmp->name, name) == 0)
+	if (strcmp(tmp->name, name) == 0 &&
+	    (tmp->addr.sa.sa_family == 0 || tmp->addr.sa.sa_family == family))
 	  break;
       }
     else if (addr && tmp->addr.sa.sa_family == AF_INET && family == AF_INET &&
diff --git a/src/option.c b/src/option.c
index 42c0198..0ca00b9 100644
--- a/src/option.c
+++ b/src/option.c
@@ -1620,8 +1620,22 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	  new->addr.sa.sa_family = AF_INET6;
 #endif
 	else
-	  new->name = opt_string_alloc(arg);
-	
+	  {
+	    char *fam = split_chr(arg, '/');
+	    new->name = opt_string_alloc(arg);
+	    new->addr.sa.sa_family = 0;
+	    if (fam)
+	      {
+		if (strcmp(fam, "4") == 0)
+		  new->addr.sa.sa_family = AF_INET;
+#ifdef HAVE_IPV6
+		else if (strcmp(fam, "6") == 0)
+		  new->addr.sa.sa_family = AF_INET6;
+#endif
+		else
+		  ret_err(gen_err);
+	      } 
+	  }
 	new->next = daemon->authinterface;
 	daemon->authinterface = new;
 	
diff --git a/src/radv.c b/src/radv.c
index 22c2d1f..93503a0 100644
--- a/src/radv.c
+++ b/src/radv.c
@@ -205,7 +205,7 @@ static void send_ra(time_t now, int iface, char *iface_name, struct in6_addr *de
   struct dhcp_netid iface_id;
   struct dhcp_opt *opt_cfg;
   struct ra_interface *ra_param = find_iface_param(iface_name);
-  int done_dns = 0;
+  int done_dns = 0, old_prefix = 0;
 #ifdef HAVE_LINUX_NETWORK
   FILE *f;
 #endif
@@ -267,7 +267,7 @@ static void send_ra(time_t now, int iface, char *iface_name, struct in6_addr *de
 	      struct in6_addr local = context->start6;
 	      int do_slaac = 0;
 
-	      parm.found_context = 1;
+	      old_prefix = 1;
 
 	      /* zero net part of address */
 	      setaddr6part(&local, addr6part(&local) & ~((context->prefix == 64) ? (u64)-1LL : (1LLU << (128 - context->prefix)) - 1LLU));
@@ -300,9 +300,14 @@ static void send_ra(time_t now, int iface, char *iface_name, struct in6_addr *de
 	up = &context->next;
     }
     
-  if (!parm.found_context)
-    return;
-    
+  /* If we're advertising only old prefixes, set router lifetime to zero. */
+  if (old_prefix && !parm.found_context)
+    ra->lifetime = htons(0);
+
+  /* No prefixes to advertise. */
+  if (!old_prefix && !parm.found_context)
+    return; 
+  
 #ifdef HAVE_LINUX_NETWORK
   /* Note that IPv6 MTU is not necessarilly the same as the IPv4 MTU
      available from SIOCGIFMTU */