zebra: justify some IPv6 ND RA timers wrt RFC

There was a regression introduced with the previous commit:
"ipv6 nd home-agent-lifetime 1800000" appeared by default in every
interface section of running-config, although this  command is
invalid in this context. Troubleshooting and bugfixing of the issue
tracked out several bugs in router advertisement procedures, some of
which are fixed in this commit.

* zebra/interface.c
  * if_zebra_new_hook(): update to treat -1 as "uninitialized"
  * nd_dump_vty(): idem
* zebra/rtadv.c
  * rtadv_send_packet(): update processing of "router lifetime" field,
    "home agent" option and "home agent lifetime" field to conform to
    RFC6275 better
  * ipv6_nd_ra_interval_msec(): update MaxRtrAdvInterval range check,
    make sure it never exceeds (initialized) AdvDefaultLifetime
  * ipv6_nd_ra_interval(): idem
  * ipv6_nd_ra_lifetime(): update AdvDefaultLifetime range check, make
    sure it never falls below MaxRtrAdvInterval
  * ipv6_nd_homeagent_lifetime(): update HomeAgentLifetime range check
  * no_ipv6_nd_ra_lifetime(): update to treat -1 as "uninitialized"
  * no_ipv6_nd_homeagent_lifetime(): idem
  * rtadv_config_write(): idem

3 files changed, 79 insertions, 18 deletions

diff --git a/zebra/interface.c b/zebra/interface.c
index 933d6425..22422594 100644
--- a/zebra/interface.c
+++ b/zebra/interface.c
@@ -76,9 +76,9 @@ if_zebra_new_hook (struct interface *ifp)
     rtadv->AdvReachableTime = 0;
     rtadv->AdvRetransTimer = 0;
     rtadv->AdvCurHopLimit = 0;
-    rtadv->AdvDefaultLifetime = RTADV_ADV_DEFAULT_LIFETIME;
+    rtadv->AdvDefaultLifetime = -1; /* derive from MaxRtrAdvInterval */
     rtadv->HomeAgentPreference = 0;
-    rtadv->HomeAgentLifetime = RTADV_ADV_DEFAULT_LIFETIME;
+    rtadv->HomeAgentLifetime = -1; /* derive from AdvDefaultLifetime */
     rtadv->AdvIntervalOption = 0;
     rtadv->DefaultPreference = RTADV_PREF_MEDIUM;
 
@@ -630,8 +630,12 @@ nd_dump_vty (struct vty *vty, struct interface *ifp)
         vty_out (vty, "  ND router advertisements are sent every "
 			"%d seconds%s", interval / 1000,
 		 VTY_NEWLINE);
-      vty_out (vty, "  ND router advertisements live for %d seconds%s",
-	       rtadv->AdvDefaultLifetime, VTY_NEWLINE);
+      if (rtadv->AdvDefaultLifetime != -1)
+	vty_out (vty, "  ND router advertisements live for %d seconds%s",
+		 rtadv->AdvDefaultLifetime, VTY_NEWLINE);
+      else
+	vty_out (vty, "  ND router advertisements lifetime tracks ra-interval%s",
+		 VTY_NEWLINE);
       vty_out (vty, "  ND router advertisement default router preference is "
 			"%s%s", rtadv_pref_strs[rtadv->DefaultPreference],
 		 VTY_NEWLINE);
@@ -642,9 +646,19 @@ nd_dump_vty (struct vty *vty, struct interface *ifp)
 	vty_out (vty, "  Hosts use stateless autoconfig for addresses.%s",
 		 VTY_NEWLINE);
       if (rtadv->AdvHomeAgentFlag)
+      {
       	vty_out (vty, "  ND router advertisements with "
 				"Home Agent flag bit set.%s",
 		 VTY_NEWLINE);
+	if (rtadv->HomeAgentLifetime != -1)
+	  vty_out (vty, "  Home Agent lifetime is %u seconds%s",
+	           rtadv->HomeAgentLifetime, VTY_NEWLINE);
+	else
+	  vty_out (vty, "  Home Agent lifetime tracks ra-lifetime%s",
+	           VTY_NEWLINE);
+	vty_out (vty, "  Home Agent preference is %u%s",
+	         rtadv->HomeAgentPreference, VTY_NEWLINE);
+      }
       if (rtadv->AdvIntervalOption)
       	vty_out (vty, "  ND router advertisements with Adv. Interval option.%s",
 		 VTY_NEWLINE);
diff --git a/zebra/interface.h b/zebra/interface.h
index 0cf66403..ea3fec57 100644
--- a/zebra/interface.h
+++ b/zebra/interface.h
@@ -69,7 +69,7 @@ struct rtadvconf
      MUST be no greater than .75 * MaxRtrAdvInterval.
 
      Default: 0.33 * MaxRtrAdvInterval */
-  int MinRtrAdvInterval;
+  int MinRtrAdvInterval; /* This field is currently unused. */
 #define RTADV_MIN_RTR_ADV_INTERVAL (0.33 * RTADV_MAX_RTR_ADV_INTERVAL)
 
   /* Unsolicited Router Advertisements' interval timer. */
@@ -131,8 +131,7 @@ struct rtadvconf
 
      Default: 3 * MaxRtrAdvInterval */
   int AdvDefaultLifetime;
-#define RTADV_ADV_DEFAULT_LIFETIME (3 * RTADV_MAX_RTR_ADV_INTERVAL)
-
+#define RTADV_MAX_RTRLIFETIME 9000 /* 2.5 hours */
 
   /* A list of prefixes to be placed in Prefix Information options in
      Router Advertisement messages sent from the interface.
diff --git a/zebra/rtadv.c b/zebra/rtadv.c
index bc1abcaf..01f88336 100644
--- a/zebra/rtadv.c
+++ b/zebra/rtadv.c
@@ -163,6 +163,7 @@ rtadv_send_packet (int sock, struct interface *ifp)
   struct rtadv_prefix *rprefix;
   u_char all_nodes_addr[] = {0xff,0x02,0,0,0,0,0,0,0,0,0,0,0,0,0,1};
   struct listnode *node;
+  u_int16_t pkt_RouterLifetime;
 
   /*
    * Allocate control message bufffer.  This is dynamic because
@@ -215,13 +216,32 @@ rtadv_send_packet (int sock, struct interface *ifp)
     rtadv->nd_ra_flags_reserved |= ND_RA_FLAG_OTHER;
   if (zif->rtadv.AdvHomeAgentFlag)
     rtadv->nd_ra_flags_reserved |= ND_RA_FLAG_HOME_AGENT;
-  rtadv->nd_ra_router_lifetime = htons (zif->rtadv.AdvDefaultLifetime);
+  /* Note that according to Neighbor Discovery (RFC 4861 [18]),
+   * AdvDefaultLifetime is by default based on the value of
+   * MaxRtrAdvInterval.  AdvDefaultLifetime is used in the Router Lifetime
+   * field of Router Advertisements.  Given that this field is expressed
+   * in seconds, a small MaxRtrAdvInterval value can result in a zero
+   * value for this field.  To prevent this, routers SHOULD keep
+   * AdvDefaultLifetime in at least one second, even if the use of
+   * MaxRtrAdvInterval would result in a smaller value. -- RFC6275, 7.5 */
+  pkt_RouterLifetime = zif->rtadv.AdvDefaultLifetime != -1 ?
+    zif->rtadv.AdvDefaultLifetime :
+    MAX (1, 0.003 * zif->rtadv.MaxRtrAdvInterval);
+  rtadv->nd_ra_router_lifetime = htons (pkt_RouterLifetime);
   rtadv->nd_ra_reachable = htonl (zif->rtadv.AdvReachableTime);
   rtadv->nd_ra_retransmit = htonl (0);
 
   len = sizeof (struct nd_router_advert);
 
-  if (zif->rtadv.AdvHomeAgentFlag)
+  /* If both the Home Agent Preference and Home Agent Lifetime are set to
+   * their default values specified above, this option SHOULD NOT be
+   * included in the Router Advertisement messages sent by this home
+   * agent. -- RFC6275, 7.4 */
+  if
+  (
+    zif->rtadv.AdvHomeAgentFlag &&
+    (zif->rtadv.HomeAgentPreference || zif->rtadv.HomeAgentLifetime != -1)
+  )
     {
       struct nd_opt_homeagent_info *ndopt_hai = 
 	(struct nd_opt_homeagent_info *)(buf + len);
@@ -229,7 +249,17 @@ rtadv_send_packet (int sock, struct interface *ifp)
       ndopt_hai->nd_opt_hai_len = 1;
       ndopt_hai->nd_opt_hai_reserved = 0;
       ndopt_hai->nd_opt_hai_preference = htons(zif->rtadv.HomeAgentPreference);
-      ndopt_hai->nd_opt_hai_lifetime = htons(zif->rtadv.HomeAgentLifetime);
+      /* 16-bit unsigned integer.  The lifetime associated with the home
+       * agent in units of seconds.  The default value is the same as the
+       * Router Lifetime, as specified in the main body of the Router
+       * Advertisement.  The maximum value corresponds to 18.2 hours.  A
+       * value of 0 MUST NOT be used. -- RFC6275, 7.5 */
+      ndopt_hai->nd_opt_hai_lifetime = htons
+      (
+        zif->rtadv.HomeAgentLifetime != -1 ?
+        zif->rtadv.HomeAgentLifetime :
+        MAX (1, pkt_RouterLifetime) /* 0 is OK for RL, but not for HAL*/
+      );
       len += sizeof(struct nd_opt_homeagent_info);
     }
 
@@ -389,6 +419,8 @@ rtadv_timer (struct thread *thread)
 	  zif->rtadv.AdvIntervalTimer -= period;
 	  if (zif->rtadv.AdvIntervalTimer <= 0)
 	    {
+	      /* FIXME: using MaxRtrAdvInterval each time isn't what section
+	         6.2.4 of RFC4861 tells to do. */
 	      zif->rtadv.AdvIntervalTimer = zif->rtadv.MaxRtrAdvInterval;
 	      rtadv_send_packet (rtadv->sock, ifp);
 	    }
@@ -707,7 +739,11 @@ DEFUN (ipv6_nd_ra_interval_msec,
 
   interval = atoi (argv[0]);
 
-  if (interval <= 0)
+  if
+  (
+    interval < 70 || interval > 1800000 ||
+    (zif->rtadv.AdvDefaultLifetime != -1 && interval > zif->rtadv.AdvDefaultLifetime * 1000)
+  )
     {
       vty_out (vty, "Invalid Router Advertisement Interval%s", VTY_NEWLINE);
       return CMD_WARNING;
@@ -743,7 +779,11 @@ DEFUN (ipv6_nd_ra_interval,
 
   interval = atoi (argv[0]);
 
-  if (interval <= 0)
+  if
+  (
+    interval < 1 || interval > 1800 ||
+    (zif->rtadv.AdvDefaultLifetime != -1 && interval > zif->rtadv.AdvDefaultLifetime)
+  )
     {
       vty_out (vty, "Invalid Router Advertisement Interval%s", VTY_NEWLINE);
       return CMD_WARNING;
@@ -803,7 +843,15 @@ DEFUN (ipv6_nd_ra_lifetime,
 
   lifetime = atoi (argv[0]);
 
-  if (lifetime < 0 || lifetime > 0xffff)
+  /* The value to be placed in the Router Lifetime field
+   * of Router Advertisements sent from the interface,
+   * in seconds.  MUST be either zero or between
+   * MaxRtrAdvInterval and 9000 seconds. -- RFC4861, 6.2.1 */
+  if
+  (
+    lifetime > RTADV_MAX_RTRLIFETIME ||
+    (lifetime != 0 && lifetime * 1000 < zif->rtadv.MaxRtrAdvInterval)
+  )
     {
       vty_out (vty, "Invalid Router Lifetime%s", VTY_NEWLINE);
       return CMD_WARNING;
@@ -828,7 +876,7 @@ DEFUN (no_ipv6_nd_ra_lifetime,
   ifp = (struct interface *) vty->index;
   zif = ifp->info;
 
-  zif->rtadv.AdvDefaultLifetime = RTADV_ADV_DEFAULT_LIFETIME;
+  zif->rtadv.AdvDefaultLifetime = -1;
 
   return CMD_SUCCESS;
 }
@@ -944,7 +992,7 @@ DEFUN (ipv6_nd_homeagent_lifetime,
 
   ha_ltime = (u_int32_t) atol (argv[0]);
 
-  if (ha_ltime > RTADV_MAX_HALIFETIME)
+  if (ha_ltime < 1 || ha_ltime > RTADV_MAX_HALIFETIME)
     {
       vty_out (vty, "Invalid Home Agent Lifetime time%s", VTY_NEWLINE);
       return CMD_WARNING;
@@ -969,7 +1017,7 @@ DEFUN (no_ipv6_nd_homeagent_lifetime,
   ifp = (struct interface *) vty->index;
   zif = ifp->info;
 
-  zif->rtadv.HomeAgentLifetime = 0;
+  zif->rtadv.HomeAgentLifetime = -1;
 
   return CMD_SUCCESS;
 }
@@ -1514,7 +1562,7 @@ rtadv_config_write (struct vty *vty, struct interface *ifp)
   if (zif->rtadv.AdvIntervalOption)
     vty_out (vty, " ipv6 nd adv-interval-option%s", VTY_NEWLINE);
 
-  if (zif->rtadv.AdvDefaultLifetime != RTADV_ADV_DEFAULT_LIFETIME)
+  if (zif->rtadv.AdvDefaultLifetime != -1)
     vty_out (vty, " ipv6 nd ra-lifetime %d%s", zif->rtadv.AdvDefaultLifetime,
 	     VTY_NEWLINE);
 
@@ -1522,7 +1570,7 @@ rtadv_config_write (struct vty *vty, struct interface *ifp)
     vty_out (vty, " ipv6 nd home-agent-preference %u%s",
 	     zif->rtadv.HomeAgentPreference, VTY_NEWLINE);
 
-  if (zif->rtadv.HomeAgentLifetime)
+  if (zif->rtadv.HomeAgentLifetime != -1)
     vty_out (vty, " ipv6 nd home-agent-lifetime %u%s",
 	     zif->rtadv.HomeAgentLifetime, VTY_NEWLINE);