diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Messages.cs b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Messages.cs
new file mode 100644
index 0000000..28e310b
--- /dev/null
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Messages.cs
@@ -0,0 +1,38 @@
+// Copyright 2018-2026 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+using System.Text;
+
+namespace ZB.MOM.NatsNet.Server;
+
+public sealed partial class ClientConnection
+{
+    internal void SendMsgToGateways(Account? account, byte[] subject, byte[]? reply, byte[] payload)
+    {
+        if (Server is not NatsServer server || account == null || subject.Length == 0)
+            return;
+
+        var outboundGateways = server.GetOutboundGatewayConnections();
+        if (outboundGateways.Count == 0)
+            return;
+
+        foreach (var gateway in outboundGateways)
+        {
+            if (!GatewayInterest(account, Encoding.ASCII.GetString(subject)))
+                continue;
+
+            var replyToSend = reply;
+            if (reply is { Length: > 0 } && gateway.Gateway != null)
+            {
+                var shouldMap = server.ShouldMapReplyForGatewaySend(reply, gateway.Gateway.UseOldPrefix);
+                if (shouldMap)
+                    replyToSend = reply;
+            }
+
+            var proto = MsgHeader(subject, replyToSend, new Internal.Subscription { Sid = Encoding.ASCII.GetBytes("1") });
+            gateway.EnqueueProto(proto);
+            gateway.EnqueueProto(payload);
+            gateway.EnqueueProto(Encoding.ASCII.GetBytes("\r\n"));
+        }
+    }
+}
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Protocol.cs b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Protocol.cs
index 895874a..b20ffa5 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Protocol.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.Gateways.Protocol.cs
@@ -99,4 +99,119 @@ public sealed partial class ClientConnection
 
         return null;
     }
+
+    internal Exception? ProcessGatewayAccountUnsub(byte[] arg)
+    {
+        if (Server is not NatsServer server)
+            return new InvalidOperationException("gateway server unavailable");
+
+        var tokens = Encoding.ASCII.GetString(arg).Split(' ', StringSplitOptions.RemoveEmptyEntries);
+        if (tokens.Length < 1)
+            return null;
+
+        if (tokens.Length == 1)
+            return null;
+
+        var accountName = tokens[0];
+        var subject = Encoding.ASCII.GetBytes(tokens[1]);
+        var queue = tokens.Length > 2 ? Encoding.ASCII.GetBytes(tokens[2]) : null;
+
+        var (account, _) = server.LookupAccount(accountName);
+        if (account == null)
+            return null;
+
+        var sub = new Internal.Subscription { Subject = subject, Queue = queue };
+        server.SendQueueSubOrUnsubToGateways(account, sub, isUnsub: true);
+        return null;
+    }
+
+    internal Exception? ProcessGatewayAccountSub(byte[] arg)
+    {
+        if (Server is not NatsServer server)
+            return new InvalidOperationException("gateway server unavailable");
+
+        var tokens = Encoding.ASCII.GetString(arg).Split(' ', StringSplitOptions.RemoveEmptyEntries);
+        if (tokens.Length < 2)
+            return null;
+
+        var accountName = tokens[0];
+        var subject = Encoding.ASCII.GetBytes(tokens[1]);
+        var queue = tokens.Length > 2 ? Encoding.ASCII.GetBytes(tokens[2]) : null;
+
+        var (account, _) = server.LookupAccount(accountName);
+        if (account == null)
+            return null;
+
+        var sub = new Internal.Subscription { Subject = subject, Queue = queue };
+        if (queue is { Length: > 0 })
+            server.SendQueueSubOrUnsubToGateways(account, sub, isUnsub: false);
+        else
+            server.MaybeSendSubOrUnsubToGateways(account, sub, isUnsub: false);
+
+        return null;
+    }
+
+    internal Exception? ProcessGatewayRUnsub(byte[] arg)
+    {
+        var tokens = Encoding.ASCII.GetString(arg).Split(' ', StringSplitOptions.RemoveEmptyEntries);
+        if (tokens.Length < 2 || Server is not NatsServer server)
+            return null;
+
+        var accountName = tokens[0];
+        var subject = Encoding.ASCII.GetBytes(tokens[1]);
+        var queue = tokens.Length > 2 ? Encoding.ASCII.GetBytes(tokens[2]) : null;
+        var (account, _) = server.LookupAccount(accountName);
+        if (account == null)
+            return null;
+
+        var sub = new Internal.Subscription { Subject = subject, Queue = queue };
+        server.MaybeSendSubOrUnsubToGateways(account, sub, isUnsub: true);
+        return null;
+    }
+
+    internal Exception? ProcessGatewayRSub(byte[] arg)
+    {
+        var tokens = Encoding.ASCII.GetString(arg).Split(' ', StringSplitOptions.RemoveEmptyEntries);
+        if (tokens.Length < 2 || Server is not NatsServer server)
+            return null;
+
+        var accountName = tokens[0];
+        var subject = Encoding.ASCII.GetBytes(tokens[1]);
+        var queue = tokens.Length > 2 ? Encoding.ASCII.GetBytes(tokens[2]) : null;
+        var (account, _) = server.LookupAccount(accountName);
+        if (account == null)
+            return null;
+
+        var sub = new Internal.Subscription { Subject = subject, Queue = queue };
+        server.MaybeSendSubOrUnsubToGateways(account, sub, isUnsub: false);
+        return null;
+    }
+
+    internal bool GatewayInterest(Account? account, string subject)
+    {
+        if (account == null || string.IsNullOrWhiteSpace(subject))
+            return false;
+
+        if (Gateway?.OutSim == null)
+            return true;
+
+        if (!Gateway.OutSim.TryGetValue(account.Name, out var outSi))
+            return true;
+
+        outSi.AcquireReadLock();
+        try
+        {
+            if (outSi.Mode == GatewayInterestMode.InterestOnly && outSi.Sl != null)
+            {
+                var match = outSi.Sl.Match(subject);
+                return match.PSubs.Count > 0 || match.QSubs.Count > 0;
+            }
+
+            return outSi.Ni == null || !outSi.Ni.Contains(subject);
+        }
+        finally
+        {
+            outSi.ReleaseReadLock();
+        }
+    }
 }
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayHandler.cs b/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayHandler.cs
index 8b1df33..60281b3 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayHandler.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayHandler.cs
@@ -9,6 +9,9 @@ namespace ZB.MOM.NatsNet.Server;
 
 internal static class GatewayHandler
 {
+    internal static readonly byte[] GwReplyPrefix = Encoding.ASCII.GetBytes("_GR_.");
+    internal static readonly byte[] OldGwReplyPrefix = Encoding.ASCII.GetBytes("$GR.");
+
     private static readonly TimeSpan DefaultSolicitGatewaysDelay = TimeSpan.FromSeconds(1);
     private static long _gatewaySolicitDelayTicks = DefaultSolicitGatewaysDelay.Ticks;
     private static int _doNotForceInterestOnlyMode;
@@ -77,6 +80,25 @@ internal static class GatewayHandler
         return Encoding.ASCII.GetBytes($"{op} {accountName} {subject}\r\n");
     }
 
+    internal static bool IsGWRoutedReply(byte[] subject)
+    {
+        return subject.AsSpan().StartsWith(GwReplyPrefix) || subject.AsSpan().StartsWith(OldGwReplyPrefix);
+    }
+
+    internal static (bool IsRouted, bool IsOldPrefix) IsGWRoutedSubjectAndIsOldPrefix(byte[] subject)
+    {
+        if (subject.AsSpan().StartsWith(OldGwReplyPrefix))
+            return (true, true);
+        if (subject.AsSpan().StartsWith(GwReplyPrefix))
+            return (true, false);
+        return (false, false);
+    }
+
+    internal static bool HasGWRoutedReplyPrefix(byte[] subject)
+    {
+        return IsGWRoutedReply(subject);
+    }
+
     private static byte[] GetHash(string value, int len)
     {
         var bytes = Encoding.UTF8.GetBytes(value);
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayTypes.cs b/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayTypes.cs
index ddeb7b4..e567081 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayTypes.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/Gateway/GatewayTypes.cs
@@ -262,6 +262,25 @@ internal sealed class SrvGateway
     {
         Outo = [.. Out.Values.OrderBy(c => c.GetRttValue()).ThenBy(c => c.Cid)];
     }
+
+    internal void OrderOutboundConnections()
+    {
+        _lock.EnterWriteLock();
+        try { OrderOutboundConnectionsLocked(); }
+        finally { _lock.ExitWriteLock(); }
+    }
+
+    internal bool ShouldMapReplyForGatewaySend(byte[] reply, bool useOldPrefix)
+    {
+        if (reply.Length == 0)
+            return false;
+
+        if (useOldPrefix)
+            return !GatewayHandler.IsGWRoutedSubjectAndIsOldPrefix(reply).IsRouted;
+
+        return !GatewayHandler.IsGWRoutedReply(reply);
+    }
+
 }
 
 /// <summary>
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.Gateways.Interest.cs b/dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.Gateways.Interest.cs
new file mode 100644
index 0000000..523d260
--- /dev/null
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.Gateways.Interest.cs
@@ -0,0 +1,77 @@
+// Copyright 2018-2026 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+using System.Net;
+using System.Text;
+using ZB.MOM.NatsNet.Server.Internal;
+
+namespace ZB.MOM.NatsNet.Server;
+
+public sealed partial class NatsServer
+{
+    internal bool ShouldMapReplyForGatewaySend(byte[] reply, bool useOldPrefix)
+    {
+        return _gateway.ShouldMapReplyForGatewaySend(reply, useOldPrefix);
+    }
+
+    internal IReadOnlyList<ClientConnection> GetInboundGatewayConnections()
+    {
+        _gateway.AcquireReadLock();
+        try { return [.. _gateway.In.Values]; }
+        finally { _gateway.ReleaseReadLock(); }
+    }
+
+    internal string GatewayAddr()
+    {
+        var opts = GetOpts();
+        var host = string.IsNullOrWhiteSpace(opts.Gateway.Host) ? opts.Host : opts.Gateway.Host;
+        return $"{host}:{opts.Gateway.Port}";
+    }
+
+    internal void SwitchAccountToInterestMode(string accountName)
+    {
+        _gateway.AcquireWriteLock();
+        try
+        {
+            foreach (var outbound in _gateway.Out.Values)
+            {
+                outbound.Gateway ??= new Gateway();
+                outbound.Gateway.OutSim ??= new System.Collections.Concurrent.ConcurrentDictionary<string, OutSide>(StringComparer.Ordinal);
+                outbound.Gateway.OutSim[accountName] = new OutSide
+                {
+                    Mode = GatewayInterestMode.InterestOnly,
+                    Ni = null,
+                };
+            }
+        }
+        finally
+        {
+            _gateway.ReleaseWriteLock();
+        }
+    }
+
+    internal void MaybeSendSubOrUnsubToGateways(Account account, Subscription sub, bool isUnsub)
+    {
+        if (sub.Subject.Length == 0)
+            return;
+
+        _gateway.AcquireReadLock();
+        try
+        {
+            foreach (var gateway in _gateway.Out.Values)
+                gateway.EnqueueProto(GatewayHandler.GwBuildSubProto(account.Name, sub, isUnsub));
+        }
+        finally
+        {
+            _gateway.ReleaseReadLock();
+        }
+    }
+
+    internal void SendQueueSubOrUnsubToGateways(Account account, Subscription sub, bool isUnsub)
+    {
+        if (sub.Queue is not { Length: > 0 })
+            return;
+
+        MaybeSendSubOrUnsubToGateways(account, sub, isUnsub);
+    }
+}
diff --git a/porting.db b/porting.db
index 07133d6..1a95955 100644
Binary files a/porting.db and b/porting.db differ