From 4e73575703c10aa2317460a4f372c5881fecccc2 Mon Sep 17 00:00:00 2001
From: Jonathan Hui <jonhui@google.com>
Date: Tue, 3 Dec 2019 08:52:38 -0800
Subject: [PATCH] [ip6] prefer RLOC source with RLOC dest in
 SelectSourceAddress() (#4377)

Prefer ML-EID for any mesh-local traffic that does not have RLOC
destination.

Credit to Rongli Sun <rongli@google.com> for identifying this issue.
---
 src/core/net/ip6.cpp | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index 23836592c..4c495c1b1 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -1364,19 +1364,6 @@ const NetifUnicastAddress *Ip6::SelectSourceAddress(MessageInfo &aMessageInfo)
                 continue;
             }
         }
-        else if ((rvalAddr->GetScope() == Address::kRealmLocalScope) && (addr->GetScope() == Address::kRealmLocalScope))
-        {
-            // Additional rule: Prefer EID
-            if (rvalAddr->GetAddress().IsRoutingLocator())
-            {
-                rvalAddr          = addr;
-                rvalPrefixMatched = candidatePrefixMatched;
-            }
-            else
-            {
-                continue;
-            }
-        }
         else if (addr->mPreferred && !rvalAddr->mPreferred)
         {
             // Rule 3: Avoid deprecated addresses
@@ -1391,6 +1378,13 @@ const NetifUnicastAddress *Ip6::SelectSourceAddress(MessageInfo &aMessageInfo)
             rvalAddr          = addr;
             rvalPrefixMatched = candidatePrefixMatched;
         }
+        else if ((candidatePrefixMatched == rvalPrefixMatched) &&
+                 (destination->IsRoutingLocator() == candidateAddr->IsRoutingLocator()))
+        {
+            // Additional rule: Prefer RLOC source for RLOC destination, EID source for anything else
+            rvalAddr          = addr;
+            rvalPrefixMatched = candidatePrefixMatched;
+        }
         else
         {
             continue;