Add mtu facility to --ra-param.
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 25e4ad9..c7d9982 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -839,7 +839,7 @@
 
 struct ra_interface {
   char *name;
-  int interval, lifetime, prio;
+  int interval, lifetime, prio, mtu;
   struct ra_interface *next;
 };
 
diff --git a/src/option.c b/src/option.c
index 3112482..30c6d4c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -488,7 +488,7 @@
 #ifdef OPTION6_PREFIX_CLASS 
   { LOPT_PREF_CLSS, ARG_DUP, "set:tag,<class>", gettext_noop("Specify DHCPv6 prefix class"), NULL },
 #endif
-  { LOPT_RA_PARAM, ARG_DUP, "<iface>,[<prio>,]<intval>[,<lifetime>]", gettext_noop("Set priority, resend-interval and router-lifetime"), NULL },
+  { LOPT_RA_PARAM, ARG_DUP, "<iface>,[mtu:<value>|off,][<prio>,]<intval>[,<lifetime>]", gettext_noop("Set MTU, priority, resend-interval and router-lifetime"), NULL },
   { LOPT_QUIET_DHCP, OPT_QUIET_DHCP, NULL, gettext_noop("Do not log routine DHCP."), NULL },
   { LOPT_QUIET_DHCP6, OPT_QUIET_DHCP6, NULL, gettext_noop("Do not log routine DHCPv6."), NULL },
   { LOPT_QUIET_RA, OPT_QUIET_RA, NULL, gettext_noop("Do not log RA."), NULL },
@@ -3706,7 +3706,18 @@
 	  struct ra_interface *new = opt_malloc(sizeof(struct ra_interface));
 	  new->lifetime = -1;
 	  new->prio = 0;
+	  new->mtu = 0;
 	  new->name = opt_string_alloc(arg);
+	  if (strcasestr(comma, "mtu:") == comma)
+	    {
+	      arg = comma + 4;
+	      if (!(comma = split(comma)))
+	        goto err;
+	      if (!strcasecmp(arg, "off"))
+	        new->mtu = -1;
+	      else if (!atoi_check(arg, &new->mtu) || new->mtu < 1280)
+	        goto err;
+	    }
 	  if (strcasestr(comma, "high") == comma || strcasestr(comma, "low") == comma)
 	    {
 	      if (*comma == 'l' || *comma == 'L')
@@ -3718,6 +3729,7 @@
 	   arg = split(comma);
 	   if (!atoi_check(comma, &new->interval) || 
 	      (arg && !atoi_check(arg, &new->lifetime)))
+err:
 	    ret_err(_("bad RA-params"));
 	  
 	  new->next = daemon->ra_interfaces;
diff --git a/src/radv.c b/src/radv.c
index 6cf9a66..70211c5 100644
--- a/src/radv.c
+++ b/src/radv.c
@@ -243,7 +243,7 @@
   struct dhcp_netid iface_id;
   struct dhcp_opt *opt_cfg;
   struct ra_interface *ra_param = find_iface_param(iface_name);
-  int done_dns = 0, old_prefix = 0;
+  int done_dns = 0, old_prefix = 0, mtu = 0;
   unsigned int min_pref_time;
 #ifdef HAVE_LINUX_NETWORK
   FILE *f;
@@ -399,22 +399,31 @@
       put_opt6_long(1000 * calc_interval(find_iface_param(iface_name)));
     }
 
+  /* Set the MTU from ra_param if any, an MTU of 0 mean automatic for linux, */
+  /* an MTU of -1 prevents the option from being sent. */
+  if (ra_param)
+    mtu = ra_param->mtu;
 #ifdef HAVE_LINUX_NETWORK
   /* Note that IPv6 MTU is not neccessarily the same as the IPv4 MTU
      available from SIOCGIFMTU */
-  sprintf(daemon->namebuff, "/proc/sys/net/ipv6/conf/%s/mtu", iface_name);
-  if ((f = fopen(daemon->namebuff, "r")))
+  if (mtu == 0)
     {
-      if (fgets(daemon->namebuff, MAXDNAME, f))
-	{
-	  put_opt6_char(ICMP6_OPT_MTU);
-	  put_opt6_char(1);
-	  put_opt6_short(0);
-	  put_opt6_long(atoi(daemon->namebuff));
-	}
-      fclose(f);
+      sprintf(daemon->namebuff, "/proc/sys/net/ipv6/conf/%s/mtu", iface_name);
+      if ((f = fopen(daemon->namebuff, "r")))
+        {
+          if (fgets(daemon->namebuff, MAXDNAME, f))
+            mtu = atoi(daemon->namebuff);
+          fclose(f);
+        }
     }
 #endif
+  if (mtu > 0)
+    {
+      put_opt6_char(ICMP6_OPT_MTU);
+      put_opt6_char(1);
+      put_opt6_short(0);
+      put_opt6_long(mtu);
+    }
      
   iface_enumerate(AF_LOCAL, &send_iface, add_lla);