diff --git a/Services/DiagnosticReportBuilder.cs b/Services/DiagnosticReportBuilder.cs
index 9d687470a..336332cdd 100644
--- a/Services/DiagnosticReportBuilder.cs
+++ b/Services/DiagnosticReportBuilder.cs
@@ -12,7 +12,7 @@ namespace ArIED61850Tester.Services;
 internal static class DiagnosticReportBuilder
 {
     private sealed record TcpProbeResult(string DeviceId, string Endpoint, string Result, string Detail);
-    private sealed record AdapterIpv4(string Name, NetworkInterfaceType Type, IPAddress Address, int PrefixLength);
+    private sealed record AdapterIpv4(string InterfaceId, string Name, NetworkInterfaceType Type, IPAddress Address, int PrefixLength);
     private sealed record RouteAnalysis(string Source, string MatchingAdapters, string AdapterMatrix, string Note);
 
     public static string BuildEmergency(
@@ -323,6 +323,8 @@ static string Safe(string value)
                     $"sqWithGIreason={stream.SequenceWithGiReason}, " +
                     $"sqWithBufOvfl={stream.SequenceWithOverflow}; " +
                     "EntryID difference/identical is not an event-loss or harmless-replay conclusion.");
+            if (stream.Buffered && stream.Findings > 0)
+                builder.AppendLine($"    BRCB context  : {ExplainBrcbContinuity(stream)}");
             if (stream.AnomalousFrames > 0)
                 builder.AppendLine($"    RCB follow-up : receivedAfterLastFinding={stream.FramesAfterLastFinding}, " +
                     $"firstFrameUtc={stream.FirstFrameReceivedAtUtc?.ToString("O") ?? "-"}, " +
@@ -384,6 +386,41 @@ static string Safe(string value)
             builder.AppendLine($"  stream list     : TRUNCATED • shown={snapshot.Streams.Count}, total={snapshot.StreamCount}");
     }
 
+    /// <summary>
+    /// IEC 61850-aware interpretation of already observed RCB metadata:
+    /// temporal context and GI reason are correlations, never proof of lost
+    /// buffered entries, a server reset, or that a sequence gap is harmless.
+    /// No extra MMS traffic, raw event retention or timer.
+    /// </summary>
+    internal static string ExplainBrcbContinuity(Iec61850ReportContinuityStreamSnapshot stream)
+    {
+        ArgumentNullException.ThrowIfNull(stream);
+        var withoutProvenGi = Math.Max(0, stream.SequenceDiscontinuities - stream.SequenceWithGiReason);
+        var context = $"sequenceDiscontinuities={stream.SequenceDiscontinuities}, " +
+            $"GI-tagged={stream.SequenceWithGiReason}, withoutConfirmedGI={withoutProvenGi}, " +
+            $"BufOvflAdvertised={stream.Overflow}";
+
+        if (stream.ActivationReturnedAtUtc is { } activation &&
+            stream.LastAnomalyReceivedAtUtc is { } anomaly &&
+            anomaly >= activation)
+        {
+            var delta = anomaly - activation;
+            var elapsed = delta.TotalMilliseconds;
+            if (double.IsFinite(elapsed))
+            {
+                context += $", lastAnomalyAfterStartMs={elapsed:0}";
+                if (delta >= TimeSpan.FromSeconds(5))
+                    context += "; late recurrence observed beyond 5s of RCB activation (NOT startup-only)";
+            }
+        }
+        else
+        {
+            context += "; timing=UNKNOWN (insufficient RCB lifecycle evidence)";
+        }
+
+        return context + "; received-frame order only, not TCP wire order, event-loss or GI causality proof";
+    }
+
     private static string Verdict(bool? value) =>
         value is true ? "YES" : value is false ? "NO" : "UNKNOWN";
 
@@ -457,8 +494,10 @@ private static RouteAnalysis AnalyzeRoute(string targetText)
             return new RouteAnalysis("unavailable", "unavailable", "unavailable", "Route analysis currently supports IPv4 endpoints.");
 
         var adapters = GetActiveIpv4Adapters();
-        var matching = adapters
+        var matchingAddresses = adapters
             .Where(item => IsInSameSubnet(item.Address, target, item.PrefixLength))
+            .ToArray();
+        var matching = matchingAddresses
             .Select(item => $"{item.Name}={item.Address}/{item.PrefixLength}")
             .Distinct(StringComparer.OrdinalIgnoreCase)
             .ToArray();
@@ -486,19 +525,12 @@ private static RouteAnalysis AnalyzeRoute(string targetText)
             source = $"unavailable ({ex.GetType().Name}: {ex.Message})";
         }
 
-        string note;
-        if (matching.Length == 0)
-        {
-            note = $"No active IPv4 adapter is in the same subnet as {target}. Check the PC adapter address, prefix length, VLAN, and static route.";
-        }
-        else if (matching.Length == 1)
-        {
-            note = $"{target} is directly reachable only through {matching[0]}. Ensure the IED is physically connected to that network.";
-        }
-        else
-        {
-            note = $"Multiple adapters match {target}; Windows route priority can select the wrong interface. Disable unused adapters or configure interface metrics/static routes.";
-        }
+        // Do not confuse multiple IP aliases on ONE KM-TEST interface with
+        // competing network adapters. Exact local IP means same-host endpoint;
+        // neither condition warrants telling operators to disable interfaces.
+        var note = ExplainIpv4Route(target,
+            matchingAddresses.Select(item => (item.InterfaceId, item.Name)).ToArray(),
+            adapters.Any(item => item.Address.Equals(target)));
 
         return new RouteAnalysis(
             source,
@@ -507,6 +539,39 @@ private static RouteAnalysis AnalyzeRoute(string targetText)
             note);
     }
 
+    /// <summary>
+    /// Pure, testable interface-aware route advice. The interface ID, not the
+    /// number of matching IPv4 addresses, defines routing ambiguity. This is
+    /// descriptive only: the actual OS routing table remains authoritative.
+    /// </summary>
+    internal static string ExplainIpv4Route(
+        IPAddress target,
+        IReadOnlyList<(string InterfaceId, string AdapterName)> matchedAddresses,
+        bool targetAssignedLocally)
+    {
+        ArgumentNullException.ThrowIfNull(target);
+        ArgumentNullException.ThrowIfNull(matchedAddresses);
+        var distinctInterfaces = matchedAddresses
+            .GroupBy(item => item.InterfaceId, StringComparer.OrdinalIgnoreCase)
+            .Select(group => group.First().AdapterName)
+            .ToArray();
+        if (targetAssignedLocally)
+            return $"Target {target} is assigned to this PC on " +
+                $"{(distinctInterfaces.Length == 0 ? "a local interface" : string.Join(", ", distinctInterfaces))}; " +
+                "this can be a same-host IED simulator. Do not infer a competing NIC from IPv4 aliases. " +
+                "Check the local MMS listener and actual OS route if connection fails.";
+        if (distinctInterfaces.Length == 0)
+            return $"No directly matching IPv4 subnet for {target}; a gateway or static route can still provide connectivity. " +
+                "Check the Windows routing table before drawing a connectivity conclusion.";
+        if (distinctInterfaces.Length == 1)
+            return $"One network interface ({distinctInterfaces[0]}) matches {target}, across " +
+                $"{matchedAddresses.Count} IPv4 address(es). IP aliases are not competing adapters; " +
+                "confirm actual OS routing and physical/virtual IED connection if needed.";
+        return $"{distinctInterfaces.Length} distinct network interfaces match {target} " +
+            $"({string.Join(", ", distinctInterfaces)}); Windows interface metrics/routing table may select " +
+            "a different path. Check the OS route before changing adapter configuration.";
+    }
+
     private static AdapterIpv4[] GetActiveIpv4Adapters()
     {
         try
@@ -517,6 +582,7 @@ private static AdapterIpv4[] GetActiveIpv4Adapters()
                 .SelectMany(adapter => adapter.GetIPProperties().UnicastAddresses
                     .Where(address => address.Address.AddressFamily == AddressFamily.InterNetwork)
                     .Select(address => new AdapterIpv4(
+                        adapter.Id,
                         adapter.Name,
                         adapter.NetworkInterfaceType,
                         address.Address,
diff --git a/tests/ARSAS.Tests/ContextAwareIec61850DiagnosisTests.cs b/tests/ARSAS.Tests/ContextAwareIec61850DiagnosisTests.cs
new file mode 100644
index 000000000..2c256ae77
--- /dev/null
+++ b/tests/ARSAS.Tests/ContextAwareIec61850DiagnosisTests.cs
@@ -0,0 +1,143 @@
+using System.Net;
+using System.Text;
+using ArIED61850Tester.Services;
+
+namespace ARSAS.Tests;
+
+/// <summary>
+/// Deterministic IEC-aware decisions: no live NIC, IED, sockets or simulator.
+/// Hardware/network routing and physical SOE completeness are separate tests.
+/// </summary>
+public sealed class ContextAwareIec61850DiagnosisTests
+{
+    private static readonly IPAddress Bcuge = IPAddress.Parse("192.16.1.33");
+
+    [Fact]
+    public void SamePhysicalInterfaceWithFiveAliases_DoesNotClaimFiveCompetingNics()
+    {
+        var addresses = Enumerable.Range(1, 5)
+            .Select(_ => (InterfaceId: "KM-TEST-GUID", AdapterName: "KM_Test")).ToArray();
+        var description = DiagnosticReportBuilder.ExplainIpv4Route(Bcuge, addresses, false);
+        Assert.Contains("One network interface (KM_Test)", description);
+        Assert.Contains("5 IPv4 address(es)", description);
+        Assert.Contains("not competing adapters", description);
+        Assert.DoesNotContain("distinct network interfaces", description);
+    }
+
+    [Fact]
+    public void DeviceIpIsLocalSimulatorEndpoint_DoesNotRecommendDisablingInterfaces()
+    {
+        var description = DiagnosticReportBuilder.ExplainIpv4Route(
+            Bcuge,
+            new[] { (InterfaceId: "KM-TEST-GUID", AdapterName: "KM_Test") },
+            targetAssignedLocally: true);
+        Assert.Contains("assigned to this PC", description);
+        Assert.Contains("same-host IED simulator", description);
+        Assert.DoesNotContain("Disable", description, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("physically connected", description, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void DifferentInterfacesWithSameFriendlyName_AreStillARealRoutingAmbiguity()
+    {
+        var description = DiagnosticReportBuilder.ExplainIpv4Route(
+            Bcuge,
+            new[]
+            {
+                (InterfaceId: "guid-1", AdapterName: "Ethernet"),
+                (InterfaceId: "guid-2", AdapterName: "Ethernet"),
+                (InterfaceId: "GUID-1", AdapterName: "Ethernet")
+            },
+            targetAssignedLocally: false);
+        Assert.Contains("2 distinct network interfaces", description);
+        Assert.Contains("routing table", description);
+    }
+
+    [Fact]
+    public void NoDirectSubnetMatch_DoesNotClaimGatewayRoutingImpossible()
+    {
+        var description = DiagnosticReportBuilder.ExplainIpv4Route(
+            Bcuge, Array.Empty<(string InterfaceId, string AdapterName)>(), false);
+        Assert.Contains("gateway or static route can still provide connectivity", description);
+        Assert.DoesNotContain("unreachable", description, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void BrcbLateRecurrence_IsNotWronglyExplainedAsStartupOnlyOrGiReset()
+    {
+        var activation = new DateTimeOffset(2026, 10, 12, 0, 26, 4, TimeSpan.Zero);
+        var stream = new Iec61850ReportContinuityStreamSnapshot
+        {
+            Rcb = "BCUGEF650/LLN0.BR.BRB_CSWI_GW010101",
+            Buffered = true,
+            Frames = 55,
+            Sequenced = 55,
+            Findings = 22,
+            SequenceDiscontinuities = 21,
+            SequenceWithGiReason = 1,
+            Overflow = 1,
+            ActivationReturnedAtUtc = activation,
+            LastAnomalyReceivedAtUtc = activation.AddSeconds(48.575)
+        };
+        var output = DiagnosticReportBuilder.ExplainBrcbContinuity(stream);
+        Assert.Contains("GI-tagged=1, withoutConfirmedGI=20", output);
+        Assert.Contains("BufOvflAdvertised=1", output);
+        Assert.Contains("lastAnomalyAfterStartMs=48575", output);
+        Assert.Contains("late recurrence observed beyond 5s", output);
+        Assert.Contains("not TCP wire order", output);
+        Assert.DoesNotContain("events were lost", output);
+
+        // Must also surface in ordinary user diagnostic, not only in helpers.
+        var builder = new StringBuilder();
+        DiagnosticReportBuilder.AppendReportContinuity(builder,
+            new Iec61850ReportContinuitySnapshot
+            {
+                Frames = 55, Sequenced = 55, Findings = 22, Streams = new[] { stream }
+            });
+        Assert.Contains("BRCB context  :", builder.ToString());
+        Assert.Contains("NOT startup-only", builder.ToString());
+    }
+
+    [Fact]
+    public void StartupOnlyObservedFrames_AreNotPromotedToCausalCertainty()
+    {
+        var activation = DateTimeOffset.UtcNow;
+        var stream = new Iec61850ReportContinuityStreamSnapshot
+        {
+            Buffered = true,
+            Findings = 2,
+            SequenceDiscontinuities = 2,
+            SequenceWithGiReason = 0,
+            ActivationReturnedAtUtc = activation,
+            LastAnomalyReceivedAtUtc = activation.AddMilliseconds(250)
+        };
+        var description = DiagnosticReportBuilder.ExplainBrcbContinuity(stream);
+        Assert.Contains("lastAnomalyAfterStartMs=250", description);
+        Assert.DoesNotContain("late recurrence", description);
+        Assert.Contains("not TCP wire order", description);
+        Assert.Contains("withoutConfirmedGI=2", description);
+    }
+
+    [Fact]
+    public void UnknownOrReversedTimestamps_DoNotFabricateLateRecurrence()
+    {
+        var now = DateTimeOffset.UtcNow;
+        var noTiming = DiagnosticReportBuilder.ExplainBrcbContinuity(
+            new Iec61850ReportContinuityStreamSnapshot
+            {
+                Buffered = true,
+                SequenceDiscontinuities = 1
+            });
+        Assert.Contains("timing=UNKNOWN", noTiming);
+        var reversed = DiagnosticReportBuilder.ExplainBrcbContinuity(
+            new Iec61850ReportContinuityStreamSnapshot
+            {
+                Buffered = true,
+                SequenceDiscontinuities = 1,
+                ActivationReturnedAtUtc = now,
+                LastAnomalyReceivedAtUtc = now.AddSeconds(-1)
+            });
+        Assert.Contains("timing=UNKNOWN", reversed);
+        Assert.DoesNotContain("late recurrence", reversed);
+    }
+}