[routing-manager] remove vicarious router discovery feature (#7727)

The vicarious router discovery feature depends on the ability to
receive Router Advertisement messages sent in response to Router
Solicitation messages from other hosts. However, this does not work
since Router Advertisement messages are often sent unicast in
response.

src/core/border_router/routing_manager.cpp

@@ -73,9 +73,6 @@ RoutingManager::RoutingManager(Instance &aInstance)
     , mDiscoveredPrefixStaleTimer(aInstance, HandleDiscoveredPrefixStaleTimer)
     , mRouterAdvertisementCount(0)
     , mLastRouterAdvertisementSendTime(TimerMilli::GetNow() - kMinDelayBetweenRtrAdvs)
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    , mVicariousRouterSolicitTimer(aInstance, HandleVicariousRouterSolicitTimer)
-#endif
     , mRouterSolicitTimer(aInstance, HandleRouterSolicitTimer)
     , mRouterSolicitCount(0)
     , mRoutingPolicyTimer(aInstance, HandleRoutingPolicyTimer)
@@ -292,9 +289,6 @@ void RoutingManager::Stop(void)
 
     mRouterAdvertisementCount = 0;
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    mVicariousRouterSolicitTimer.Stop();
-#endif
     mRouterSolicitTimer.Stop();
     mRouterSolicitCount = 0;
 
@@ -787,10 +781,6 @@ void RoutingManager::StartRouterSolicitationDelay(void)
 
     OT_ASSERT(mRouterSolicitCount == 0);
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    mVicariousRouterSolicitTimer.Stop();
-#endif
-
     static_assert(kMaxRtrSolicitationDelay > 0, "invalid maximum Router Solicitation delay");
     randomDelay = Random::NonCrypto::GetUint32InRange(0, Time::SecToMsec(kMaxRtrSolicitationDelay));
 
@@ -991,27 +981,6 @@ bool RoutingManager::IsValidOnLinkPrefix(const Ip6::Prefix &aOnLinkPrefix)
     return !aOnLinkPrefix.IsLinkLocal() && !aOnLinkPrefix.IsMulticast();
 }
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-void RoutingManager::HandleVicariousRouterSolicitTimer(Timer &aTimer)
-{
-    aTimer.Get<RoutingManager>().HandleVicariousRouterSolicitTimer();
-}
-
-void RoutingManager::HandleVicariousRouterSolicitTimer(void)
-{
-    LogInfo("Vicarious router solicitation time out");
-
-    for (const ExternalPrefix &prefix : mDiscoveredPrefixes)
-    {
-        if (prefix.mTimeLastUpdate <= mTimeVicariousRouterSolicitStart)
-        {
-            StartRouterSolicitationDelay();
-            break;
-        }
-    }
-}
-#endif
-
 void RoutingManager::HandleRouterSolicitTimer(Timer &aTimer)
 {
     aTimer.Get<RoutingManager>().HandleRouterSolicitTimer();
@@ -1118,14 +1087,6 @@ void RoutingManager::HandleRouterSolicit(const InfraIf::Icmp6Packet &aPacket, co
     LogInfo("Received Router Solicitation from %s on %s", aSrcAddress.ToString().AsCString(),
             mInfraIf.ToString().AsCString());
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    if (!mVicariousRouterSolicitTimer.IsRunning())
-    {
-        mTimeVicariousRouterSolicitStart = TimerMilli::GetNow();
-        mVicariousRouterSolicitTimer.Start(Time::SecToMsec(kVicariousSolicitationTime));
-    }
-#endif
-
     // Schedule routing policy evaluation with random jitter to respond with Router Advertisement.
     StartRoutingPolicyEvaluationJitter(kRaReplyJitter);
 }

src/core/border_router/routing_manager.hpp

@@ -237,13 +237,6 @@ private:
     // The value is chosen in range of [`kMaxRtrAdvInterval` upper bound (1800s), `kDefaultOnLinkPrefixLifetime`].
     static constexpr uint32_t kRtrAdvStaleTime = 1800;
 
-    // The VICARIOUS_SOLICIT_TIME in seconds. The Routing Manager will consider
-    // the discovered prefixes invalid if they are not refreshed after receiving
-    // a Router Solicitation message.
-    // The value is equal to Router Solicitation timeout.
-    static constexpr uint32_t kVicariousSolicitationTime =
-        kRtrSolicitationInterval * (kMaxRtrSolicitations - 1) + kMaxRtrSolicitationDelay;
-
     static_assert(kMinRtrAdvInterval <= 3 * kMaxRtrAdvInterval / 4, "invalid RA intervals");
     static_assert(kDefaultOmrPrefixLifetime >= kMaxRtrAdvInterval, "invalid default OMR prefix lifetime");
     static_assert(kDefaultOnLinkPrefixLifetime >= kMaxRtrAdvInterval, "invalid default on-link prefix lifetime");
@@ -327,10 +320,6 @@ private:
     void  SendRouterAdvertisement(const OmrPrefixArray &aNewOmrPrefixes, const Ip6::Prefix *aNewOnLinkPrefix);
     bool  IsRouterSolicitationInProgress(void) const;
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    static void HandleVicariousRouterSolicitTimer(Timer &aTimer);
-    void        HandleVicariousRouterSolicitTimer(void);
-#endif
     static void HandleRouterSolicitTimer(Timer &aTimer);
     void        HandleRouterSolicitTimer(void);
     static void HandleDiscoveredPrefixInvalidTimer(Timer &aTimer);
@@ -416,10 +405,6 @@ private:
     uint32_t  mRouterAdvertisementCount;
     TimeMilli mLastRouterAdvertisementSendTime;
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-    TimerMilli mVicariousRouterSolicitTimer;
-    TimeMilli  mTimeVicariousRouterSolicitStart;
-#endif
     TimerMilli mRouterSolicitTimer;
     TimeMilli  mTimeRouterSolicitStart;
     uint8_t    mRouterSolicitCount;

src/core/config/border_router.h

@@ -75,16 +75,6 @@
 #define OPENTHREAD_CONFIG_BORDER_ROUTING_MAX_DISCOVERED_PREFIXES 8
 #endif
 
-/**
- * @def OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
- *
- * Define to 1 to enable Border Routing Vicarious Router Solicitation.
- *
- */
-#ifndef OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
-#define OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE 1
-#endif
-
 /**
  * @def OPENTHREAD_CONFIG_BORDER_ROUTING_NAT64_ENABLE
  *

src/core/config/openthread-core-config-check.h

@@ -623,4 +623,8 @@
 #error "OPENTHREAD_CONFIG_PLATFORM_CSL_UNCERT was removed and no longer supported"
 #endif
 
+#ifdef OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE
+#error "OPENTHREAD_CONFIG_BORDER_ROUTING_VICARIOUS_RS_ENABLE was removed and no longer supported"
+#endif
+
 #endif // OPENTHREAD_CORE_CONFIG_CHECK_H_

tests/scripts/thread-cert/border_router/test_on_link_prefix.py

@@ -34,7 +34,7 @@ import config
 import thread_cert
 
 # Test description:
-#   This test verifies Vicarious Router Solicitation.
+#   This test verifies on-link prefix configuration.
 #
 # Topology:
 #    -------------(eth)----------------------------