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/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 ae5fad5..6ccf4b1 100644
--- a/src/option.c
+++ b/src/option.c
@@ -1615,8 +1615,22 @@ 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;