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

1 files changed, 18 insertions, 4 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);