RFC 4191 Default Router Preference support for router advertisements

Adds "ipv6 nd router-preference (high|medium|low)" and
"no ipv6 nd router-preference" interface commands.

Files modified:

   doc/ipv6.texi
   zebra/interface.c
   zebra/interface.h
   zebra/rtadv.c
   zebra/rtadv.h

Signed-off-by: Chris Caputo <ccaputo@alt.net>

5 files changed, 91 insertions, 3 deletions

diff --git a/doc/ipv6.texi b/doc/ipv6.texi
index 910253c8..a78a92fe 100644
--- a/doc/ipv6.texi
+++ b/doc/ipv6.texi
@@ -150,6 +150,13 @@ in milliseconds, between successive unsolicited Router Advertisements.
 Default: not set
 @end deffn
 
+@deffn {Interface Command} {ipv6 nd router-preference (high|medium|low)} {}
+@deffnx {Interface Command} {no ipv6 nd router-preference} {}
+Set default router preference in IPv6 router advertisements per RFC4191.
+
+Default: medium
+@end deffn
+
 @example
 @group
 interface eth0
@@ -160,4 +167,5 @@ interface eth0
 
 For more information see @cite{RFC2462 (IPv6 Stateless Address Autoconfiguration)}
 , @cite{RFC2461 (Neighbor Discovery for IP Version 6 (IPv6))}
-and @cite{RFC3775 (Mobility Support in IPv6 (Mobile IPv6))}.
+, @cite{RFC3775 (Mobility Support in IPv6 (Mobile IPv6))}
+and @cite{RFC4191 (Default Router Preferences and More-Specific Routes)}.
diff --git a/zebra/interface.c b/zebra/interface.c
index 3e4867c4..9dfb6d50 100644
--- a/zebra/interface.c
+++ b/zebra/interface.c
@@ -41,6 +41,11 @@
 #include "zebra/debug.h"
 #include "zebra/irdp.h"
 
+#ifdef RTADV
+/* Order is intentional.  Matches RFC4191.  This array is also used for
+   command matching, so only modify with care. */
+const char *rtadv_pref_strs[] = { "medium", "high", "INVALID", "low", 0 };
+#endif /* RTADV */
 
 /* Called when new interface is added. */
 static int
@@ -75,6 +80,7 @@ if_zebra_new_hook (struct interface *ifp)
     rtadv->HomeAgentPreference = 0;
     rtadv->HomeAgentLifetime = RTADV_ADV_DEFAULT_LIFETIME;
     rtadv->AdvIntervalOption = 0;
+    rtadv->DefaultPreference = RTADV_PREF_MEDIUM;
 
     rtadv->AdvPrefixList = list_new ();
   }    
@@ -622,6 +628,9 @@ nd_dump_vty (struct vty *vty, struct interface *ifp)
 		 VTY_NEWLINE);
       vty_out (vty, "  ND router advertisements live for %d seconds%s",
 	       rtadv->AdvDefaultLifetime, VTY_NEWLINE);
+      vty_out (vty, "  ND router advertisement default router preference is "
+			"%s%s", rtadv_pref_strs[rtadv->DefaultPreference],
+		 VTY_NEWLINE);
       if (rtadv->AdvManagedFlag)
 	vty_out (vty, "  Hosts use DHCP to obtain routable addresses.%s",
 		 VTY_NEWLINE);
diff --git a/zebra/interface.h b/zebra/interface.h
index 968430ab..0cf66403 100644
--- a/zebra/interface.h
+++ b/zebra/interface.h
@@ -46,7 +46,7 @@
 #endif
 
 #ifdef RTADV
-/* Router advertisement parameter.  From RFC2461 and RFC3775. */
+/* Router advertisement parameter.  From RFC2461, RFC3775 and RFC4191. */
 struct rtadvconf
 {
   /* A flag indicating whether or not the router sends periodic Router
@@ -171,6 +171,13 @@ struct rtadvconf
 
      Default: FALSE */
   int AdvIntervalOption;
+
+  /* The value to be placed in the Default Router Preference field of
+     a router advertisement. See [RFC 4191 2.1 & 2.2]
+
+     Default: 0 (medium) */
+  int DefaultPreference;
+#define RTADV_PREF_MEDIUM 0x0 /* Per RFC4191. */
 };
 
 #endif /* RTADV */
diff --git a/zebra/rtadv.c b/zebra/rtadv.c
index dd2be812..ff96648a 100644
--- a/zebra/rtadv.c
+++ b/zebra/rtadv.c
@@ -206,7 +206,12 @@ rtadv_send_packet (int sock, struct interface *ifp)
   rtadv->nd_ra_cksum = 0;
 
   rtadv->nd_ra_curhoplimit = 64;
-  rtadv->nd_ra_flags_reserved = 0;
+
+  /* RFC4191: Default Router Preference is 0 if Router Lifetime is 0. */
+  rtadv->nd_ra_flags_reserved =
+    zif->rtadv.AdvDefaultLifetime == 0 ? 0 : zif->rtadv.DefaultPreference;
+  rtadv->nd_ra_flags_reserved <<= 3;
+
   if (zif->rtadv.AdvManagedFlag)
     rtadv->nd_ra_flags_reserved |= ND_RA_FLAG_MANAGED;
   if (zif->rtadv.AdvOtherConfigFlag)
@@ -1364,6 +1369,56 @@ DEFUN (no_ipv6_nd_prefix,
 
   return CMD_SUCCESS;
 }
+
+DEFUN (ipv6_nd_router_preference,
+       ipv6_nd_router_preference_cmd,
+       "ipv6 nd router-preference (high|medium|low)",
+       "Interface IPv6 config commands\n"
+       "Neighbor discovery\n"
+       "Default router preference\n"
+       "High default router preference\n"
+       "Low default router preference\n"
+       "Medium default router preference (default)\n")
+{
+  struct interface *ifp;
+  struct zebra_if *zif;
+  int i = 0;
+
+  ifp = (struct interface *) vty->index;
+  zif = ifp->info;
+
+  while (0 != rtadv_pref_strs[i])
+    {
+      if (strncmp (argv[0], rtadv_pref_strs[i], 1) == 0)
+	{
+	  zif->rtadv.DefaultPreference = i;
+	  return CMD_SUCCESS;
+	}
+      i++;
+    }
+
+  return CMD_ERR_NO_MATCH;
+}
+
+DEFUN (no_ipv6_nd_router_preference,
+       no_ipv6_nd_router_preference_cmd,
+       "no ipv6 nd router-preference",
+       NO_STR
+       "Interface IPv6 config commands\n"
+       "Neighbor discovery\n"
+       "Default router preference\n")
+{
+  struct interface *ifp;
+  struct zebra_if *zif;
+
+  ifp = (struct interface *) vty->index;
+  zif = ifp->info;
+
+  zif->rtadv.DefaultPreference = RTADV_PREF_MEDIUM; /* Default per RFC4191. */
+
+  return CMD_SUCCESS;
+}
+
 /* Write configuration about router advertisement. */
 void
 rtadv_config_write (struct vty *vty, struct interface *ifp)
@@ -1411,6 +1466,11 @@ rtadv_config_write (struct vty *vty, struct interface *ifp)
   if (zif->rtadv.AdvOtherConfigFlag)
     vty_out (vty, " ipv6 nd other-config-flag%s", VTY_NEWLINE);
 
+  if (zif->rtadv.DefaultPreference != RTADV_PREF_MEDIUM)
+    vty_out (vty, " ipv6 nd router-preference %s%s",
+	     rtadv_pref_strs[zif->rtadv.DefaultPreference],
+	     VTY_NEWLINE);
+
   for (ALL_LIST_ELEMENTS_RO (zif->rtadv.AdvPrefixList, node, rprefix))
     {
       vty_out (vty, " ipv6 nd prefix %s/%d",
@@ -1532,6 +1592,8 @@ rtadv_init (void)
   install_element (INTERFACE_NODE, &ipv6_nd_prefix_noval_rtaddr_cmd);
   install_element (INTERFACE_NODE, &ipv6_nd_prefix_prefix_cmd);
   install_element (INTERFACE_NODE, &no_ipv6_nd_prefix_cmd);
+  install_element (INTERFACE_NODE, &ipv6_nd_router_preference_cmd);
+  install_element (INTERFACE_NODE, &no_ipv6_nd_router_preference_cmd);
 }
 
 static int
diff --git a/zebra/rtadv.h b/zebra/rtadv.h
index abd1c6fc..d8d263d0 100644
--- a/zebra/rtadv.h
+++ b/zebra/rtadv.h
@@ -94,4 +94,6 @@ struct nd_opt_homeagent_info {  /* Home Agent info */
 } __attribute__((__packed__));
 #endif
 
+extern const char *rtadv_pref_strs[];
+
 #endif /* _ZEBRA_RTADV_H */