[routing-manager] skip self-prepared RA when learning host RA header (#7846)

This commit updates how `RoutingManager` learns the RA header from
host daemons. It adds a new method to determine whether a received RA
message is prepared by the `RoutingManager` itself by checking the
options (PIO and RIO) from the RA message. When learning/updating the
host RA header, we check and skip over such self-prepared RA
messages.

src/core/border_router/routing_manager.cpp

@@ -913,6 +913,68 @@ void RoutingManager::SendRouterAdvertisement(const OmrPrefixArray &aNewOmrPrefix
     }
 }
 
+bool RoutingManager::IsReceivdRouterAdvertFromManager(const Ip6::Nd::RouterAdvertMessage &aRaMessage) const
+{
+    // Determines whether or not a received RA message was prepared by
+    // by `RoutingManager` itself.
+
+    bool        isFromManager = false;
+    uint16_t    rioCount      = 0;
+    Ip6::Prefix prefix;
+
+    VerifyOrExit(aRaMessage.ContainsAnyOptions());
+
+    for (const Ip6::Nd::Option &option : aRaMessage)
+    {
+        switch (option.GetType())
+        {
+        case Ip6::Nd::Option::kTypePrefixInfo:
+        {
+            // PIO should match `mLocalOnLinkPrefix`.
+
+            const Ip6::Nd::PrefixInfoOption &pio = static_cast<const Ip6::Nd::PrefixInfoOption &>(option);
+
+            VerifyOrExit(pio.IsValid());
+            pio.GetPrefix(prefix);
+
+            VerifyOrExit(prefix == mLocalOnLinkPrefix);
+            break;
+        }
+
+        case Ip6::Nd::Option::kTypeRouteInfo:
+        {
+            // RIO (with non-zero lifetime) should match entries from
+            // `mAdvertisedOmrPrefixes`. We keep track of the number
+            // of matched RIOs and check after the loop ends that all
+            // entries were seen.
+
+            const Ip6::Nd::RouteInfoOption &rio = static_cast<const Ip6::Nd::RouteInfoOption &>(option);
+
+            VerifyOrExit(rio.IsValid());
+            rio.GetPrefix(prefix);
+
+            if (rio.GetRouteLifetime() != 0)
+            {
+                VerifyOrExit(mAdvertisedOmrPrefixes.ContainsMatching(prefix));
+                rioCount++;
+            }
+
+            break;
+        }
+
+        default:
+            ExitNow();
+        }
+    }
+
+    VerifyOrExit(rioCount == mAdvertisedOmrPrefixes.GetLength());
+
+    isFromManager = true;
+
+exit:
+    return isFromManager;
+}
+
 bool RoutingManager::IsValidBrUlaPrefix(const Ip6::Prefix &aBrUlaPrefix)
 {
     return aBrUlaPrefix.mLength == kBrUlaPrefixLength && aBrUlaPrefix.mPrefix.mFields.m8[0] == 0xfd;
@@ -1174,6 +1236,14 @@ void RoutingManager::UpdateRouterAdvertHeader(const Ip6::Nd::RouterAdvertMessage
 
     Ip6::Nd::RouterAdvertMessage::Header oldHeader;
 
+    if (aRouterAdvertMessage != nullptr)
+    {
+        // We skip and do not update RA header if the received RA message
+        // was not prepared and sent by `RoutingManager` itself.
+
+        VerifyOrExit(!IsReceivdRouterAdvertFromManager(*aRouterAdvertMessage));
+    }
+
     oldHeader                       = mRouterAdvertHeader;
     mTimeRouterAdvMessageLastUpdate = TimerMilli::GetNow();
 
@@ -1203,6 +1273,9 @@ void RoutingManager::UpdateRouterAdvertHeader(const Ip6::Nd::RouterAdvertMessage
 
         StartRoutingPolicyEvaluationJitter(kRoutingPolicyEvaluationJitter);
     }
+
+exit:
+    return;
 }
 
 void RoutingManager::ResetDiscoveredPrefixStaleTimer(void)

src/core/border_router/routing_manager.hpp

@@ -478,6 +478,7 @@ private:
     void HandleDiscoveredPrefixTableChanged(void);
     bool NetworkDataContainsOmrPrefix(const Ip6::Prefix &aPrefix) const;
     void UpdateRouterAdvertHeader(const Ip6::Nd::RouterAdvertMessage *aRouterAdvertMessage);
+    bool IsReceivdRouterAdvertFromManager(const Ip6::Nd::RouterAdvertMessage &aRaMessage) const;
     void ResetDiscoveredPrefixStaleTimer(void);
 
     static bool IsValidBrUlaPrefix(const Ip6::Prefix &aBrUlaPrefix);