[routing-manager] handle deprecated OMR prefix (#7703)

This commit enhances routing-manager to avoid using deprecated
(i.e. P_preferred=false) OMR prefixes as the winning OMR prefix, but
still sends RA RIO for the deprecating OMR prefixes.

src/core/border_router/routing_manager.cpp

@@ -401,11 +401,14 @@ void RoutingManager::EvaluateOmrPrefix(OmrPrefixArray &aNewOmrPrefixes)
             continue;
         }
 
-        if (electedOmrPrefix == nullptr || onMeshPrefixConfig.mPreference > electedOmrPrefixPreference ||
-            (onMeshPrefixConfig.mPreference == electedOmrPrefixPreference && prefix < *electedOmrPrefix))
+        if (onMeshPrefixConfig.mPreferred)
         {
-            electedOmrPrefix           = aNewOmrPrefixes.Back();
-            electedOmrPrefixPreference = onMeshPrefixConfig.mPreference;
+            if (electedOmrPrefix == nullptr || onMeshPrefixConfig.mPreference > electedOmrPrefixPreference ||
+                (onMeshPrefixConfig.mPreference == electedOmrPrefixPreference && prefix < *electedOmrPrefix))
+            {
+                electedOmrPrefix           = aNewOmrPrefixes.Back();
+                electedOmrPrefixPreference = onMeshPrefixConfig.mPreference;
+            }
         }
 
         if (prefix == mLocalOmrPrefix)
@@ -416,9 +419,9 @@ void RoutingManager::EvaluateOmrPrefix(OmrPrefixArray &aNewOmrPrefixes)
 
     // Decide if we need to add or remove our local OMR prefix.
 
-    if (aNewOmrPrefixes.IsEmpty())
+    if (electedOmrPrefix == nullptr)
     {
-        LogInfo("EvaluateOmrPrefix: No valid OMR prefixes found in Thread network");
+        LogInfo("EvaluateOmrPrefix: No preferred OMR prefixes found in Thread network");
 
         if (PublishLocalOmrPrefix() == kErrorNone)
         {
@@ -430,8 +433,6 @@ void RoutingManager::EvaluateOmrPrefix(OmrPrefixArray &aNewOmrPrefixes)
     }
     else
     {
-        OT_ASSERT(electedOmrPrefix != nullptr);
-
         if (*electedOmrPrefix == mLocalOmrPrefix)
         {
             IgnoreError(PublishLocalOmrPrefix());

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

@@ -31,6 +31,8 @@ import unittest
 
 import config
 import thread_cert
+from pktverify.consts import ICMPV6_RA_OPT_TYPE_RIO
+from pktverify.packet_verifier import PacketVerifier
 
 # Test description:
 # The purpose of this test case is to verify that BR can handle manually added OMR prefixes properly.
@@ -89,6 +91,28 @@ class ManualOmrsPrefix(thread_cert.TestCase):
         self._test_manual_omr_prefix('2002::/64', 'pars', expect_withdraw=False)
         # Add a smaller but invalid OMR prefix (P_stable = 0). Verify BR_1 does not withdraw its OMR prefix.
         self._test_manual_omr_prefix('2003::/64', 'paro', expect_withdraw=False)
+        # Add a deprecating OMR prefix (P_preferred = 0). Verify BR_1 does not withdraw its OMR prefix.
+        self._test_manual_omr_prefix('2004::/64', 'aros', expect_withdraw=False)
+
+        self.collect_ipaddrs()
+        self.collect_extra_vars(BR_1_OMR_PREFIX=br1.get_br_omr_prefix())
+
+    def verify(self, pv: PacketVerifier):
+        pkts = pv.pkts
+        pv.summary.show()
+
+        BR_1_ETH = pv.vars['BR_1_ETH']
+
+        BR_1_OMR_PREFIX = pv.vars['BR_1_OMR_PREFIX']
+        assert BR_1_OMR_PREFIX.endswith('::/64')
+        BR_1_OMR_PREFIX = BR_1_OMR_PREFIX[:-3]
+
+        # Filter all ICMPv6 RA messages advertised by BR_1
+        ra_pkts = pkts.filter_eth_src(BR_1_ETH).filter_icmpv6_nd_ra()
+
+        # Verify BR_1 sends RA RIO for both BR OMR prefix and deprecating OMR prefix (i.e. 2004::/64)
+        ra_pkts.filter(lambda p: ICMPV6_RA_OPT_TYPE_RIO in p.icmpv6.opt.type and '2004::' in p.icmpv6.opt.prefix and
+                       BR_1_OMR_PREFIX in p.icmpv6.opt.prefix).must_next()
 
     def _test_manual_omr_prefix(self, prefix, flags, expect_withdraw, prf='med'):
         br1 = self.nodes[BR_1]

tests/scripts/thread-cert/pktverify/consts.py

@@ -397,6 +397,8 @@ ICMPV6_TYPE_PARAMETER_PROBLEM = 4
 ICMPV6_TYPE_ECHO_REQUEST = 128
 ICMPV6_TYPE_ECHO_REPLY = 129
 
+ICMPV6_RA_OPT_TYPE_RIO = 24
+
 THREAD_ALLOWED_ICMPV6_TYPES = [
     ICMPV6_TYPE_DESTINATION_UNREACHABLE,
     ICMPV6_TYPE_PACKET_TO_BIG,

tests/scripts/thread-cert/pktverify/layer_fields.py

@@ -477,13 +477,7 @@ _LAYER_FIELDS = {
     'icmpv6.opt.route_lifetime': _auto,
     'icmpv6.opt.route_info.flag.route_preference': _auto,
     'icmpv6.opt.route_info.flag.reserved': _auto,
-    'icmpv6.opt.prefix.valid_lifetime': _auto,
-    'icmpv6.opt.prefix.preferred_lifetime': _auto,
-    'icmpv6.opt.prefix.length': _list(_auto),
-    'icmpv6.opt.prefix.flag.reserved': _auto,
-    'icmpv6.opt.prefix.flag.r': _auto,
-    'icmpv6.opt.prefix.flag.l': _auto,
-    'icmpv6.opt.prefix.flag.a': _auto,
+    'icmpv6.opt.prefix': _list(_ipv6_addr),
     'icmpv6.opt.length': _list(_auto),
     'icmpv6.opt.reserved': _str,
     'icmpv6.nd.ra.router_lifetime': _auto,