diff --git a/src/libraries/Common/src/Interop/Windows/WinSock/Interop.getsockopt.cs b/src/libraries/Common/src/Interop/Windows/WinSock/Interop.getsockopt.cs
index 1e9334800edcb..77d7420a6c57e 100644
--- a/src/libraries/Common/src/Interop/Windows/WinSock/Interop.getsockopt.cs
+++ b/src/libraries/Common/src/Interop/Windows/WinSock/Interop.getsockopt.cs
@@ -22,7 +22,7 @@ internal static extern SocketError getsockopt(
             [In] SafeSocketHandle socketHandle,
             [In] SocketOptionLevel optionLevel,
             [In] SocketOptionName optionName,
-            [Out] byte[]? optionValue,
+            [Out] byte[] optionValue,
             [In, Out] ref int optionLength);
 
         [DllImport(Interop.Libraries.Ws2_32, SetLastError = true)]
diff --git a/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs b/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
index a806974cea2e0..56e85e8e488db 100644
--- a/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
+++ b/src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs
@@ -235,8 +235,9 @@ public Socket(System.Net.Sockets.SocketType socketType, System.Net.Sockets.Proto
         public bool ExclusiveAddressUse { get { throw null; } set { } }
         public System.IntPtr Handle { get { throw null; } }
         public bool IsBound { get { throw null; } }
-        public System.Net.Sockets.LingerOption LingerState { get { throw null; } set { } }
-        public System.Net.EndPoint LocalEndPoint { get { throw null; } }
+        [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
+        public System.Net.Sockets.LingerOption? LingerState { get { throw null; } set { } }
+        public System.Net.EndPoint? LocalEndPoint { get { throw null; } }
         public bool MulticastLoopback { get { throw null; } set { } }
         public bool NoDelay { get { throw null; } set { } }
         public static bool OSSupportsIPv4 { get { throw null; } }
@@ -245,7 +246,7 @@ public Socket(System.Net.Sockets.SocketType socketType, System.Net.Sockets.Proto
         public System.Net.Sockets.ProtocolType ProtocolType { get { throw null; } }
         public int ReceiveBufferSize { get { throw null; } set { } }
         public int ReceiveTimeout { get { throw null; } set { } }
-        public System.Net.EndPoint RemoteEndPoint { get { throw null; } }
+        public System.Net.EndPoint? RemoteEndPoint { get { throw null; } }
         public System.Net.Sockets.SafeSocketHandle SafeHandle { get { throw null; } }
         public int SendBufferSize { get { throw null; } set { } }
         public int SendTimeout { get { throw null; } set { } }
@@ -258,27 +259,27 @@ public Socket(System.Net.Sockets.SocketType socketType, System.Net.Sockets.Proto
         public bool UseOnlyOverlappedIO { get { throw null; } set { } }
         public System.Net.Sockets.Socket Accept() { throw null; }
         public bool AcceptAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
-        public System.IAsyncResult BeginAccept(System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginAccept(int receiveSize, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginAccept(System.Net.Sockets.Socket acceptSocket, int receiveSize, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(System.Net.EndPoint remoteEP, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(System.Net.IPAddress address, int port, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(System.Net.IPAddress[] addresses, int port, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(string host, int port, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginDisconnect(bool reuseSocket, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceive(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceive(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceive(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceive(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceiveFrom(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginReceiveMessageFrom(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSendFile(string fileName, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSendFile(string fileName, byte[] preBuffer, byte[] postBuffer, System.Net.Sockets.TransmitFileOptions flags, System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginSendTo(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP, System.AsyncCallback callback, object state) { throw null; }
+        public System.IAsyncResult BeginAccept(System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginAccept(int receiveSize, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginAccept(System.Net.Sockets.Socket? acceptSocket, int receiveSize, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(System.Net.EndPoint remoteEP, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(System.Net.IPAddress address, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(System.Net.IPAddress[] addresses, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(string host, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginDisconnect(bool reuseSocket, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginReceive(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult? BeginReceive(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginReceive(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult? BeginReceive(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginReceiveFrom(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginReceiveMessageFrom(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginSend(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult? BeginSend(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginSend(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult? BeginSend(System.Collections.Generic.IList<System.ArraySegment<byte>> buffers, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginSendFile(string? fileName, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginSendFile(string? fileName, byte[]? preBuffer, byte[]? postBuffer, System.Net.Sockets.TransmitFileOptions flags, System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginSendTo(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP, System.AsyncCallback? callback, object? state) { throw null; }
         public void Bind(System.Net.EndPoint localEP) { }
         public static void CancelConnectAsync(System.Net.Sockets.SocketAsyncEventArgs e) { }
         public void Close() { }
@@ -294,8 +295,8 @@ public void Disconnect(bool reuseSocket) { }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
         public System.Net.Sockets.SocketInformation DuplicateAndClose(int targetProcessId) { throw null; }
-        public System.Net.Sockets.Socket EndAccept(out byte[] buffer, System.IAsyncResult asyncResult) { throw null; }
-        public System.Net.Sockets.Socket EndAccept(out byte[] buffer, out int bytesTransferred, System.IAsyncResult asyncResult) { throw null; }
+        public System.Net.Sockets.Socket EndAccept(out byte[]? buffer, System.IAsyncResult asyncResult) { throw null; }
+        public System.Net.Sockets.Socket EndAccept(out byte[]? buffer, out int bytesTransferred, System.IAsyncResult asyncResult) { throw null; }
         public System.Net.Sockets.Socket EndAccept(System.IAsyncResult asyncResult) { throw null; }
         public void EndConnect(System.IAsyncResult asyncResult) { }
         public void EndDisconnect(System.IAsyncResult asyncResult) { }
@@ -308,11 +309,11 @@ public void EndDisconnect(System.IAsyncResult asyncResult) { }
         public void EndSendFile(System.IAsyncResult asyncResult) { }
         public int EndSendTo(System.IAsyncResult asyncResult) { throw null; }
         ~Socket() { }
-        public object GetSocketOption(System.Net.Sockets.SocketOptionLevel optionLevel, System.Net.Sockets.SocketOptionName optionName) { throw null; }
+        public object? GetSocketOption(System.Net.Sockets.SocketOptionLevel optionLevel, System.Net.Sockets.SocketOptionName optionName) { throw null; }
         public void GetSocketOption(System.Net.Sockets.SocketOptionLevel optionLevel, System.Net.Sockets.SocketOptionName optionName, byte[] optionValue) { }
         public byte[] GetSocketOption(System.Net.Sockets.SocketOptionLevel optionLevel, System.Net.Sockets.SocketOptionName optionName, int optionLength) { throw null; }
-        public int IOControl(int ioControlCode, byte[] optionInValue, byte[] optionOutValue) { throw null; }
-        public int IOControl(System.Net.Sockets.IOControlCode ioControlCode, byte[] optionInValue, byte[] optionOutValue) { throw null; }
+        public int IOControl(int ioControlCode, byte[]? optionInValue, byte[]? optionOutValue) { throw null; }
+        public int IOControl(System.Net.Sockets.IOControlCode ioControlCode, byte[]? optionInValue, byte[]? optionOutValue) { throw null; }
         public void Listen() { }
         public void Listen(int backlog) { }
         public bool Poll(int microSeconds, System.Net.Sockets.SelectMode mode) { throw null; }
@@ -335,7 +336,7 @@ public void Listen(int backlog) { }
         public bool ReceiveFromAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
         public int ReceiveMessageFrom(byte[] buffer, int offset, int size, ref System.Net.Sockets.SocketFlags socketFlags, ref System.Net.EndPoint remoteEP, out System.Net.Sockets.IPPacketInformation ipPacketInformation) { throw null; }
         public bool ReceiveMessageFromAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
-        public static void Select(System.Collections.IList checkRead, System.Collections.IList checkWrite, System.Collections.IList checkError, int microSeconds) { }
+        public static void Select(System.Collections.IList? checkRead, System.Collections.IList? checkWrite, System.Collections.IList? checkError, int microSeconds) { }
         public int Send(byte[] buffer) { throw null; }
         public int Send(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags) { throw null; }
         public int Send(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode) { throw null; }
@@ -348,8 +349,8 @@ public static void Select(System.Collections.IList checkRead, System.Collections
         public int Send(System.ReadOnlySpan<byte> buffer, System.Net.Sockets.SocketFlags socketFlags) { throw null; }
         public int Send(System.ReadOnlySpan<byte> buffer, System.Net.Sockets.SocketFlags socketFlags, out System.Net.Sockets.SocketError errorCode) { throw null; }
         public bool SendAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
-        public void SendFile(string fileName) { }
-        public void SendFile(string fileName, byte[] preBuffer, byte[] postBuffer, System.Net.Sockets.TransmitFileOptions flags) { }
+        public void SendFile(string? fileName) { }
+        public void SendFile(string? fileName, byte[]? preBuffer, byte[]? postBuffer, System.Net.Sockets.TransmitFileOptions flags) { }
         public bool SendPacketsAsync(System.Net.Sockets.SocketAsyncEventArgs e) { throw null; }
         public int SendTo(byte[] buffer, int offset, int size, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
         public int SendTo(byte[] buffer, int size, System.Net.Sockets.SocketFlags socketFlags, System.Net.EndPoint remoteEP) { throw null; }
@@ -367,30 +368,30 @@ public partial class SocketAsyncEventArgs : System.EventArgs, System.IDisposable
     {
         public SocketAsyncEventArgs() { }
         public SocketAsyncEventArgs(bool unsafeSuppressExecutionContextFlow) { }
-        public System.Net.Sockets.Socket AcceptSocket { get { throw null; } set { } }
-        public byte[] Buffer { get { throw null; } }
-        public System.Collections.Generic.IList<System.ArraySegment<byte>> BufferList { get { throw null; } set { } }
+        public System.Net.Sockets.Socket? AcceptSocket { get { throw null; } set { } }
+        public byte[]? Buffer { get { throw null; } }
+        public System.Collections.Generic.IList<System.ArraySegment<byte>>? BufferList { get { throw null; } set { } }
         public int BytesTransferred { get { throw null; } }
-        public System.Exception ConnectByNameError { get { throw null; } }
-        public System.Net.Sockets.Socket ConnectSocket { get { throw null; } }
+        public System.Exception? ConnectByNameError { get { throw null; } }
+        public System.Net.Sockets.Socket? ConnectSocket { get { throw null; } }
         public int Count { get { throw null; } }
         public bool DisconnectReuseSocket { get { throw null; } set { } }
         public System.Net.Sockets.SocketAsyncOperation LastOperation { get { throw null; } }
         public System.Memory<byte> MemoryBuffer { get { throw null; } }
         public int Offset { get { throw null; } }
         public System.Net.Sockets.IPPacketInformation ReceiveMessageFromPacketInfo { get { throw null; } }
-        public System.Net.EndPoint RemoteEndPoint { get { throw null; } set { } }
-        public System.Net.Sockets.SendPacketsElement[] SendPacketsElements { get { throw null; } set { } }
+        public System.Net.EndPoint? RemoteEndPoint { get { throw null; } set { } }
+        public System.Net.Sockets.SendPacketsElement[]? SendPacketsElements { get { throw null; } set { } }
         public System.Net.Sockets.TransmitFileOptions SendPacketsFlags { get { throw null; } set { } }
         public int SendPacketsSendSize { get { throw null; } set { } }
         public System.Net.Sockets.SocketError SocketError { get { throw null; } set { } }
         public System.Net.Sockets.SocketFlags SocketFlags { get { throw null; } set { } }
-        public object UserToken { get { throw null; } set { } }
-        public event System.EventHandler<System.Net.Sockets.SocketAsyncEventArgs> Completed { add { } remove { } }
+        public object? UserToken { get { throw null; } set { } }
+        public event System.EventHandler<System.Net.Sockets.SocketAsyncEventArgs>? Completed { add { } remove { } }
         public void Dispose() { }
         ~SocketAsyncEventArgs() { }
         protected virtual void OnCompleted(System.Net.Sockets.SocketAsyncEventArgs e) { }
-        public void SetBuffer(byte[] buffer, int offset, int count) { }
+        public void SetBuffer(byte[]? buffer, int offset, int count) { }
         public void SetBuffer(int offset, int count) { }
         public void SetBuffer(System.Memory<byte> buffer) { }
     }
@@ -516,7 +517,7 @@ public enum SocketShutdown
     public static partial class SocketTaskExtensions
     {
         public static System.Threading.Tasks.Task<System.Net.Sockets.Socket> AcceptAsync(this System.Net.Sockets.Socket socket) { throw null; }
-        public static System.Threading.Tasks.Task<System.Net.Sockets.Socket> AcceptAsync(this System.Net.Sockets.Socket socket, System.Net.Sockets.Socket acceptSocket) { throw null; }
+        public static System.Threading.Tasks.Task<System.Net.Sockets.Socket> AcceptAsync(this System.Net.Sockets.Socket socket, System.Net.Sockets.Socket? acceptSocket) { throw null; }
         public static System.Threading.Tasks.Task ConnectAsync(this System.Net.Sockets.Socket socket, System.Net.EndPoint remoteEP) { throw null; }
         public static System.Threading.Tasks.Task ConnectAsync(this System.Net.Sockets.Socket socket, System.Net.IPAddress address, int port) { throw null; }
         public static System.Threading.Tasks.Task ConnectAsync(this System.Net.Sockets.Socket socket, System.Net.IPAddress[] addresses, int port) { throw null; }
@@ -551,15 +552,16 @@ public TcpClient(string hostname, int port) { }
         public System.Net.Sockets.Socket Client { get { throw null; } set { } }
         public bool Connected { get { throw null; } }
         public bool ExclusiveAddressUse { get { throw null; } set { } }
-        public System.Net.Sockets.LingerOption LingerState { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
+        public System.Net.Sockets.LingerOption? LingerState { get { throw null; } set { } }
         public bool NoDelay { get { throw null; } set { } }
         public int ReceiveBufferSize { get { throw null; } set { } }
         public int ReceiveTimeout { get { throw null; } set { } }
         public int SendBufferSize { get { throw null; } set { } }
         public int SendTimeout { get { throw null; } set { } }
-        public System.IAsyncResult BeginConnect(System.Net.IPAddress address, int port, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(System.Net.IPAddress[] addresses, int port, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginConnect(string host, int port, System.AsyncCallback requestCallback, object state) { throw null; }
+        public System.IAsyncResult BeginConnect(System.Net.IPAddress address, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(System.Net.IPAddress[] addresses, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginConnect(string host, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
         public void Close() { }
         public void Connect(System.Net.IPAddress address, int port) { }
         public void Connect(System.Net.IPAddress[] ipAddresses, int port) { }
@@ -589,8 +591,8 @@ public TcpListener(System.Net.IPEndPoint localEP) { }
         public System.Net.Sockets.TcpClient AcceptTcpClient() { throw null; }
         public System.Threading.Tasks.Task<System.Net.Sockets.TcpClient> AcceptTcpClientAsync() { throw null; }
         public void AllowNatTraversal(bool allowed) { }
-        public System.IAsyncResult BeginAcceptSocket(System.AsyncCallback callback, object state) { throw null; }
-        public System.IAsyncResult BeginAcceptTcpClient(System.AsyncCallback callback, object state) { throw null; }
+        public System.IAsyncResult BeginAcceptSocket(System.AsyncCallback? callback, object? state) { throw null; }
+        public System.IAsyncResult BeginAcceptTcpClient(System.AsyncCallback? callback, object? state) { throw null; }
         public static System.Net.Sockets.TcpListener Create(int port) { throw null; }
         public System.Net.Sockets.Socket EndAcceptSocket(System.IAsyncResult asyncResult) { throw null; }
         public System.Net.Sockets.TcpClient EndAcceptTcpClient(System.IAsyncResult asyncResult) { throw null; }
@@ -626,10 +628,10 @@ public UdpClient(string hostname, int port) { }
         public bool MulticastLoopback { get { throw null; } set { } }
         public short Ttl { get { throw null; } set { } }
         public void AllowNatTraversal(bool allowed) { }
-        public System.IAsyncResult BeginReceive(System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, System.Net.IPEndPoint endPoint, System.AsyncCallback requestCallback, object state) { throw null; }
-        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, string hostname, int port, System.AsyncCallback requestCallback, object state) { throw null; }
+        public System.IAsyncResult BeginReceive(System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, System.Net.IPEndPoint? endPoint, System.AsyncCallback? requestCallback, object? state) { throw null; }
+        public System.IAsyncResult BeginSend(byte[] datagram, int bytes, string? hostname, int port, System.AsyncCallback? requestCallback, object? state) { throw null; }
         public void Close() { }
         public void Connect(System.Net.IPAddress addr, int port) { }
         public void Connect(System.Net.IPEndPoint endPoint) { }
@@ -644,14 +646,14 @@ public void JoinMulticastGroup(int ifindex, System.Net.IPAddress multicastAddr)
         public void JoinMulticastGroup(System.Net.IPAddress multicastAddr) { }
         public void JoinMulticastGroup(System.Net.IPAddress multicastAddr, int timeToLive) { }
         public void JoinMulticastGroup(System.Net.IPAddress multicastAddr, System.Net.IPAddress localAddress) { }
-        public byte[] Receive(ref System.Net.IPEndPoint remoteEP) { throw null; }
+        public byte[] Receive(ref System.Net.IPEndPoint? remoteEP) { throw null; }
         public System.Threading.Tasks.Task<System.Net.Sockets.UdpReceiveResult> ReceiveAsync() { throw null; }
         public int Send(byte[] dgram, int bytes) { throw null; }
-        public int Send(byte[] dgram, int bytes, System.Net.IPEndPoint endPoint) { throw null; }
-        public int Send(byte[] dgram, int bytes, string hostname, int port) { throw null; }
+        public int Send(byte[] dgram, int bytes, System.Net.IPEndPoint? endPoint) { throw null; }
+        public int Send(byte[] dgram, int bytes, string? hostname, int port) { throw null; }
         public System.Threading.Tasks.Task<int> SendAsync(byte[] datagram, int bytes) { throw null; }
-        public System.Threading.Tasks.Task<int> SendAsync(byte[] datagram, int bytes, System.Net.IPEndPoint endPoint) { throw null; }
-        public System.Threading.Tasks.Task<int> SendAsync(byte[] datagram, int bytes, string hostname, int port) { throw null; }
+        public System.Threading.Tasks.Task<int> SendAsync(byte[] datagram, int bytes, System.Net.IPEndPoint? endPoint) { throw null; }
+        public System.Threading.Tasks.Task<int> SendAsync(byte[] datagram, int bytes, string? hostname, int port) { throw null; }
     }
     public partial struct UdpReceiveResult : System.IEquatable<System.Net.Sockets.UdpReceiveResult>
     {
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlKeepAlive.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlKeepAlive.Windows.cs
index b671284b4664a..178ff72cbe29d 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlKeepAlive.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/IOControlKeepAlive.Windows.cs
@@ -23,7 +23,7 @@ internal sealed class IOControlKeepAlive
 
         public static bool IsNeeded => !s_supportsKeepAliveViaSocketOption;
 
-        public static SocketError Get(SafeSocketHandle handle, SocketOptionName optionName, byte[]? optionValueSeconds, ref int optionLength)
+        public static SocketError Get(SafeSocketHandle handle, SocketOptionName optionName, byte[] optionValueSeconds, ref int optionLength)
         {
             if (optionValueSeconds == null ||
                 !BitConverter.TryWriteBytes(optionValueSeconds.AsSpan(), Get(handle, optionName)))
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
index 3bbb650c7d715..804b9d35343e3 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Unix.cs
@@ -138,7 +138,7 @@ private static void CheckTransmitFileOptions(TransmitFileOptions flags)
             }
         }
 
-        private void SendFileInternal(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
+        private void SendFileInternal(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
         {
             CheckTransmitFileOptions(flags);
 
@@ -219,7 +219,7 @@ private async Task SendFileInternalAsync(FileStream? fileStream, byte[]? preBuff
             }
         }
 
-        private IAsyncResult BeginSendFileInternal(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
+        private IAsyncResult BeginSendFileInternal(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
         {
             CheckTransmitFileOptions(flags);
 
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
index b469a8f54a04b..d6060321e5d27 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.Windows.cs
@@ -333,7 +333,7 @@ private Socket GetOrCreateAcceptSocket(Socket? acceptSocket, bool checkDisconnec
             return acceptSocket;
         }
 
-        private void SendFileInternal(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
+        private void SendFileInternal(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
         {
             // Open the file, if any
             FileStream? fileStream = OpenFile(fileName);
@@ -363,7 +363,7 @@ private void SendFileInternal(string fileName, byte[]? preBuffer, byte[]? postBu
             }
         }
 
-        private IAsyncResult BeginSendFileInternal(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
+        private IAsyncResult BeginSendFileInternal(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
         {
             FileStream? fileStream = OpenFile(fileName);
 
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
index cab50e3235cec..35d7cd0e0dd2e 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs
@@ -1217,12 +1217,12 @@ public int Send(ReadOnlySpan<byte> buffer, SocketFlags socketFlags, out SocketEr
             return bytesTransferred;
         }
 
-        public void SendFile(string fileName)
+        public void SendFile(string? fileName)
         {
             SendFile(fileName, null, null, TransmitFileOptions.UseDefaultWorkerThread);
         }
 
-        public void SendFile(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
+        public void SendFile(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);
 
@@ -1706,7 +1706,7 @@ public int ReceiveFrom(byte[] buffer, ref EndPoint remoteEP)
             return ReceiveFrom(buffer, 0, buffer != null ? buffer.Length : 0, SocketFlags.None, ref remoteEP);
         }
 
-        public int IOControl(int ioControlCode, byte[] optionInValue, byte[] optionOutValue)
+        public int IOControl(int ioControlCode, byte[]? optionInValue, byte[]? optionOutValue)
         {
             ThrowIfDisposed();
 
@@ -1729,7 +1729,7 @@ public int IOControl(int ioControlCode, byte[] optionInValue, byte[] optionOutVa
             return realOptionLength;
         }
 
-        public int IOControl(IOControlCode ioControlCode, byte[] optionInValue, byte[] optionOutValue)
+        public int IOControl(IOControlCode ioControlCode, byte[]? optionInValue, byte[]? optionOutValue)
         {
             return IOControl(unchecked((int)ioControlCode), optionInValue, optionOutValue);
         }
@@ -1856,7 +1856,7 @@ public void SetSocketOption(SocketOptionLevel optionLevel, SocketOptionName opti
             return optionValue;
         }
 
-        public void GetSocketOption(SocketOptionLevel optionLevel, SocketOptionName optionName, byte[]? optionValue)
+        public void GetSocketOption(SocketOptionLevel optionLevel, SocketOptionName optionName, byte[] optionValue)
         {
             ThrowIfDisposed();
 
@@ -1867,7 +1867,7 @@ public void GetSocketOption(SocketOptionLevel optionLevel, SocketOptionName opti
                 _handle,
                 optionLevel,
                 optionName,
-                optionValue,
+                optionValue!,
                 ref optionLength);
 
             if (NetEventSource.IsEnabled) NetEventSource.Info(this, $"Interop.Winsock.getsockopt returns errorCode:{errorCode}");
@@ -2459,7 +2459,7 @@ private SocketError DoBeginSend(byte[] buffer, int offset, int size, SocketFlags
             return errorCode;
         }
 
-        public IAsyncResult BeginSend(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, AsyncCallback callback, object state)
+        public IAsyncResult BeginSend(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, AsyncCallback? callback, object? state)
         {
             SocketError errorCode;
             IAsyncResult? result = BeginSend(buffers, socketFlags, out errorCode, callback, state);
@@ -2470,7 +2470,7 @@ public IAsyncResult BeginSend(IList<ArraySegment<byte>> buffers, SocketFlags soc
             return result!;
         }
 
-        public IAsyncResult? BeginSend(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, out SocketError errorCode, AsyncCallback callback, object state)
+        public IAsyncResult? BeginSend(IList<ArraySegment<byte>> buffers, SocketFlags socketFlags, out SocketError errorCode, AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);
             ThrowIfDisposed();
@@ -2592,12 +2592,12 @@ public int EndSend(IAsyncResult asyncResult, out SocketError errorCode)
             return bytesTransferred;
         }
 
-        public IAsyncResult BeginSendFile(string fileName, AsyncCallback callback, object state)
+        public IAsyncResult BeginSendFile(string? fileName, AsyncCallback? callback, object? state)
         {
             return BeginSendFile(fileName, null, null, TransmitFileOptions.UseDefaultWorkerThread, callback, state);
         }
 
-        public IAsyncResult BeginSendFile(string fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
+        public IAsyncResult BeginSendFile(string? fileName, byte[]? preBuffer, byte[]? postBuffer, TransmitFileOptions flags, AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);
 
@@ -3040,7 +3040,7 @@ public int EndReceive(IAsyncResult asyncResult, out SocketError errorCode)
             return bytesTransferred;
         }
 
-        public IAsyncResult BeginReceiveMessageFrom(byte[] buffer, int offset, int size, SocketFlags socketFlags, ref EndPoint remoteEP, AsyncCallback callback, object state)
+        public IAsyncResult BeginReceiveMessageFrom(byte[] buffer, int offset, int size, SocketFlags socketFlags, ref EndPoint remoteEP, AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled)
             {
@@ -3445,7 +3445,7 @@ public int EndReceiveFrom(IAsyncResult asyncResult, ref EndPoint endPoint)
         // Return Value:
         //
         //    IAsyncResult - Async result used to retrieve resultant new socket
-        public IAsyncResult BeginAccept(AsyncCallback callback, object state)
+        public IAsyncResult BeginAccept(AsyncCallback? callback, object? state)
         {
             if (!_isDisconnected)
             {
@@ -3459,13 +3459,13 @@ public IAsyncResult BeginAccept(AsyncCallback callback, object state)
             return null; // unreachable
         }
 
-        public IAsyncResult BeginAccept(int receiveSize, AsyncCallback callback, object state)
+        public IAsyncResult BeginAccept(int receiveSize, AsyncCallback? callback, object? state)
         {
             return BeginAccept(null, receiveSize, callback, state);
         }
 
         // This is the truly async version that uses AcceptEx.
-        public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCallback callback, object state)
+        public IAsyncResult BeginAccept(Socket? acceptSocket, int receiveSize, AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);
             ThrowIfDisposed();
@@ -3865,6 +3865,11 @@ public bool DisconnectAsync(SocketAsyncEventArgs e)
             // Throw if socket disposed
             ThrowIfDisposed();
 
+            if (e == null)
+            {
+                throw new ArgumentNullException(nameof(e));
+            }
+
             // Prepare for and make the native call.
             e.StartOperationCommon(this, SocketAsyncOperation.Disconnect);
             SocketError socketError = SocketError.Success;
@@ -5023,7 +5028,7 @@ private void ValidateBlockingMode()
         partial void ValidateForMultiConnect(bool isMultiEndpoint);
 
         // Helper for SendFile implementations
-        private static FileStream? OpenFile(string name) => string.IsNullOrEmpty(name) ? null : File.OpenRead(name);
+        private static FileStream? OpenFile(string? name) => string.IsNullOrEmpty(name) ? null : File.OpenRead(name);
 
         private void UpdateReceiveSocketErrorForDisposed(ref SocketError socketError, int bytesTransferred)
         {
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
index 99bbb5ac3525b..9a38815d8b15b 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.cs
@@ -318,7 +318,7 @@ internal void CopyBufferFrom(SocketAsyncEventArgs source)
             }
         }
 
-        public void SetBuffer(byte[] buffer, int offset, int count)
+        public void SetBuffer(byte[]? buffer, int offset, int count)
         {
             StartConfiguring();
             try
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs
index 6ecf6e0cd6a98..59626a56d999b 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs
@@ -1098,7 +1098,7 @@ public static SocketError ReceiveFrom(SafeSocketHandle handle, byte[] buffer, in
             return completed ? errorCode : SocketError.WouldBlock;
         }
 
-        public static SocketError WindowsIoctl(SafeSocketHandle handle, int ioControlCode, byte[] optionInValue, byte[] optionOutValue, out int optionLength)
+        public static SocketError WindowsIoctl(SafeSocketHandle handle, int ioControlCode, byte[]? optionInValue, byte[]? optionOutValue, out int optionLength)
         {
             // Three codes are called out in the Winsock IOCTLs documentation as "The following Unix IOCTL codes (commands) are supported." They are
             // also the three codes available for use with ioctlsocket on Windows. Developers should be discouraged from using Socket.IOControl in
@@ -1316,7 +1316,7 @@ public static unsafe SocketError GetSockOpt(SafeSocketHandle handle, SocketOptio
             return err == Interop.Error.SUCCESS ? SocketError.Success : GetSocketErrorForErrorCode(err);
         }
 
-        public static unsafe SocketError GetSockOpt(SafeSocketHandle handle, SocketOptionLevel optionLevel, SocketOptionName optionName, byte[]? optionValue, ref int optionLength)
+        public static unsafe SocketError GetSockOpt(SafeSocketHandle handle, SocketOptionLevel optionLevel, SocketOptionName optionName, byte[] optionValue, ref int optionLength)
         {
             int optLen = optionLength;
 
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
index 9871f1a62a7dd..8eab7ef2c9b9a 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Windows.cs
@@ -716,7 +716,7 @@ public static SocketError GetSockOpt(SafeSocketHandle handle, SocketOptionLevel
             return errorCode == SocketError.SocketError ? GetLastSocketError() : SocketError.Success;
         }
 
-        public static SocketError GetSockOpt(SafeSocketHandle handle, SocketOptionLevel optionLevel, SocketOptionName optionName, byte[]? optionValue, ref int optionLength)
+        public static SocketError GetSockOpt(SafeSocketHandle handle, SocketOptionLevel optionLevel, SocketOptionName optionName, byte[] optionValue, ref int optionLength)
         {
             if (optionLevel == SocketOptionLevel.Tcp &&
                 (optionName == SocketOptionName.TcpKeepAliveTime || optionName == SocketOptionName.TcpKeepAliveInterval) &&
diff --git a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
index 80bb22935143e..a16e8f1033d40 100644
--- a/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
+++ b/src/libraries/System.Net.Sockets/src/System/Net/Sockets/TCPListener.cs
@@ -224,7 +224,7 @@ public TcpClient AcceptTcpClient()
             return returnValue;
         }
 
-        public IAsyncResult BeginAcceptSocket(AsyncCallback callback, object state)
+        public IAsyncResult BeginAcceptSocket(AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);
 
@@ -262,7 +262,7 @@ public Socket EndAcceptSocket(IAsyncResult asyncResult)
             return socket;
         }
 
-        public IAsyncResult BeginAcceptTcpClient(AsyncCallback callback, object state)
+        public IAsyncResult BeginAcceptTcpClient(AsyncCallback? callback, object? state)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this);