From ea9a6d2b14f794c756575bbbea668ac029acb1bb Mon Sep 17 00:00:00 2001
From: Rongli Sun <rongli@google.com>
Date: Fri, 21 Jun 2019 13:19:40 +0800
Subject: [PATCH] [network-diagnostic] specify link-local source for link-local
 destination (#3935)

In #3284, the source for network diagnostic is explicitly specified as RLOC.
However when link-local address is the destination, link-local source is
preferred.
---
 src/core/thread/network_diagnostic.cpp | 30 +++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/core/thread/network_diagnostic.cpp b/src/core/thread/network_diagnostic.cpp
index 193a60be7..f82ce3eda 100644
--- a/src/core/thread/network_diagnostic.cpp
+++ b/src/core/thread/network_diagnostic.cpp
@@ -115,7 +115,15 @@ otError NetworkDiagnostic::SendDiagnosticGet(const Ip6::Address &aDestination,
         SuccessOrExit(error = message->Append(aTlvTypes, aCount));
     }
 
-    messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    if (aDestination.IsLinkLocal() || aDestination.IsLinkLocalMulticast())
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetLinkLocalAddress());
+    }
+    else
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    }
+
     messageInfo.SetPeerAddr(aDestination);
     messageInfo.SetPeerPort(kCoapUdpPort);
 
@@ -499,7 +507,15 @@ void NetworkDiagnostic::HandleDiagnosticGetQuery(Coap::Message &aMessage, const
         SuccessOrExit(error = message->SetPayloadMarker());
     }
 
-    messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    if (aMessageInfo.GetSockAddr().IsLinkLocal() || aMessageInfo.GetSockAddr().IsLinkLocalMulticast())
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetLinkLocalAddress());
+    }
+    else
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    }
+
     messageInfo.SetPeerAddr(aMessageInfo.GetPeerAddr());
     messageInfo.SetPeerPort(kCoapUdpPort);
 
@@ -601,7 +617,15 @@ otError NetworkDiagnostic::SendDiagnosticReset(const Ip6::Address &aDestination,
         SuccessOrExit(error = message->Append(aTlvTypes, aCount));
     }
 
-    messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    if (aDestination.IsLinkLocal() || aDestination.IsLinkLocalMulticast())
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetLinkLocalAddress());
+    }
+    else
+    {
+        messageInfo.SetSockAddr(Get<Mle::MleRouter>().GetMeshLocal16());
+    }
+
     messageInfo.SetPeerAddr(aDestination);
     messageInfo.SetPeerPort(kCoapUdpPort);