diff --git a/src/esockd.erl b/src/esockd.erl
index f2c0f09..ee42d82 100644
--- a/src/esockd.erl
+++ b/src/esockd.erl
@@ -21,18 +21,26 @@
 -export([start/0]).
 
 %% Core API
--export([ open/4
-        , open_udp/4
-        , open_dtls/4
+-export([ open/3
+        , open_udp/3
+        , open_dtls/3
         , close/2
         , close/1
+        %% Legacy API
+        , open/4
+        , open_udp/4
+        , open_dtls/4
         ]).
 
 -export([ reopen/1
         , reopen/2
         ]).
 
--export([ child_spec/4
+-export([ child_spec/3
+        , udp_child_spec/3
+        , dtls_child_spec/3
+        %% Legacy API
+        , child_spec/4
         , udp_child_spec/4
         , dtls_child_spec/4
         ]).
@@ -65,7 +73,9 @@
 
 %% Utility functions
 -export([ merge_opts/2
+        , changed_opts/2
         , parse_opt/1
+        , start_mfargs/3
         , ulimit/0
         , fixaddr/1
         , to_string/1
@@ -94,6 +104,7 @@
 -type(option() :: {acceptors, pos_integer()}
                 | {max_connections, pos_integer()}
                 | {max_conn_rate, conn_limit()}
+                | {connection_mfargs, mfargs()}
                 | {access_rules, [esockd_access:rule()]}
                 | {shutdown, brutal_kill | infinity | pos_integer()}
                 | tune_buffer | {tune_buffer, boolean()}
@@ -106,8 +117,10 @@
 
 -type(host() :: inet:ip_address() | string()).
 -type(listen_on() :: inet:port_number() | {host(), inet:port_number()}).
--type ssl_options() :: [{handshake_timeout, pos_integer()} | ssl_option()].
--type dtls_options() :: [{handshake_timeout, pos_integer()} | ssl_option()].
+-type ssl_options() :: [ssl_custom_option() | ssl_option()].
+-type dtls_options() :: [ssl_custom_option() | ssl_option()].
+-type ssl_custom_option() :: {handshake_timeout, pos_integer()}
+                           | {gc_after_handshake, boolean()}.
 -type listener_ref() :: {proto(), listen_on()}.
 
 %%--------------------------------------------------------------------
@@ -123,35 +136,51 @@ start() ->
 %% Open & Close
 
 %% @doc Open a TCP or SSL listener
--spec(open(atom(), listen_on(), [option()], mfargs()) -> {ok, pid()} | {error, term()}).
-open(Proto, Port, Opts, MFA) when is_atom(Proto), is_integer(Port) ->
-	esockd_sup:start_listener(Proto, Port, Opts, MFA);
-open(Proto, {Host, Port}, Opts, MFA) when is_atom(Proto), is_integer(Port) ->
+-spec open(atom(), listen_on(), options()) -> {ok, pid()} | {error, term()}.
+open(Proto, Port, Opts) when is_atom(Proto), is_integer(Port) ->
+	esockd_sup:start_child(child_spec(Proto, Port, Opts));
+open(Proto, {Host, Port}, Opts) when is_atom(Proto), is_integer(Port) ->
     {IPAddr, _Port} = fixaddr({Host, Port}),
     case proplists:get_value(ip, tcp_options(Opts)) of
         undefined -> ok;
         IPAddr    -> ok;
         Other     -> error({badmatch, Other})
     end,
-	esockd_sup:start_listener(Proto, {IPAddr, Port}, Opts, MFA).
+	esockd_sup:start_child(child_spec(Proto, {IPAddr, Port}, Opts)).
 
 %% @private
 tcp_options(Opts) ->
     proplists:get_value(tcp_options, Opts, []).
 
+%% @doc Open a TCP or SSL listener
+-spec open(atom(), listen_on(), [option()], mfargs()) -> {ok, pid()} | {error, term()}.
+open(Proto, Port, Opts, MFA) ->
+	open(Proto, Port, merge_mfargs(Opts, MFA)).
+
 %% @doc Open a UDP listener
--spec(open_udp(atom(), listen_on(), [option()], mfargs())
-     -> {ok, pid()}
-      | {error, term()}).
+-spec open_udp(atom(), listen_on(), [option()])
+      -> {ok, pid()} | {error, term()}.
+open_udp(Proto, Port, Opts) ->
+    esockd_sup:start_child(udp_child_spec(Proto, Port, Opts)).
+
+%% @doc Open a UDP listener
+-spec open_udp(atom(), listen_on(), [option()], mfargs())
+      -> {ok, pid()} | {error, term()}.
 open_udp(Proto, Port, Opts, MFA) ->
-    esockd_sup:start_child(udp_child_spec(Proto, Port, Opts, MFA)).
+    open_udp(Proto, Port, merge_mfargs(Opts, MFA)).
+
+%% @doc Open a DTLS listener
+-spec open_dtls(atom(), listen_on(), options())
+      -> {ok, pid()} | {error, term()}.
+open_dtls(Proto, ListenOn, Opts) ->
+    esockd_sup:start_child(dtls_child_spec(Proto, ListenOn, Opts)).
 
 %% @doc Open a DTLS listener
 -spec(open_dtls(atom(), listen_on(), options(), mfargs())
      -> {ok, pid()}
       | {error, term()}).
 open_dtls(Proto, ListenOn, Opts, MFA) ->
-    esockd_sup:start_child(dtls_child_spec(Proto, ListenOn, Opts, MFA)).
+    open_dtls(Proto, ListenOn, merge_mfargs(Opts, MFA)).
 
 %% @doc Close the listener
 -spec(close({atom(), listen_on()}) -> ok | {error, term()}).
@@ -176,22 +205,42 @@ reopen(Proto, ListenOn) when is_atom(Proto) ->
 
 %% @doc Create a Child spec for a TCP/SSL Listener. It is a convenient method
 %% for creating a Child spec to hang on another Application supervisor.
--spec(child_spec(atom(), listen_on(), [option()], mfargs())
-      -> supervisor:child_spec()).
+-spec child_spec(atom(), listen_on(), options())
+      -> supervisor:child_spec().
+child_spec(Proto, ListenOn, Opts) when is_atom(Proto) ->
+    esockd_sup:child_spec(Proto, fixaddr(ListenOn), Opts).
+
+-spec child_spec(atom(), listen_on(), options(), mfargs())
+      -> supervisor:child_spec().
 child_spec(Proto, ListenOn, Opts, MFA) when is_atom(Proto) ->
-    esockd_sup:child_spec(Proto, fixaddr(ListenOn), Opts, MFA).
+    child_spec(Proto, ListenOn, merge_mfargs(Opts, MFA)).
+
+%% @doc Create a Child spec for a UDP Listener.
+-spec udp_child_spec(atom(), listen_on(), options())
+     -> supervisor:child_spec().
+udp_child_spec(Proto, Port, Opts) ->
+    esockd_sup:udp_child_spec(Proto, fixaddr(Port), Opts).
 
 %% @doc Create a Child spec for a UDP Listener.
--spec(udp_child_spec(atom(), listen_on(), options(), mfargs())
-     -> supervisor:child_spec()).
+-spec udp_child_spec(atom(), listen_on(), options(), mfargs())
+     -> supervisor:child_spec().
 udp_child_spec(Proto, Port, Opts, MFA) ->
-    esockd_sup:udp_child_spec(Proto, fixaddr(Port), Opts, MFA).
+    udp_child_spec(Proto, Port, merge_mfargs(Opts, MFA)).
 
 %% @doc Create a Child spec for a DTLS Listener.
--spec(dtls_child_spec(atom(), listen_on(), options(), mfargs())
-     -> supervisor:child_spec()).
+-spec dtls_child_spec(atom(), listen_on(), options())
+     -> supervisor:child_spec().
+dtls_child_spec(Proto, ListenOn, Opts) ->
+    esockd_sup:dtls_child_spec(Proto, fixaddr(ListenOn), Opts).
+
+%% @doc Create a Child spec for a DTLS Listener.
+-spec dtls_child_spec(atom(), listen_on(), options(), mfargs())
+     -> supervisor:child_spec().
 dtls_child_spec(Proto, ListenOn, Opts, MFA) ->
-    esockd_sup:dtls_child_spec(Proto, fixaddr(ListenOn), Opts, MFA).
+    dtls_child_spec(Proto, ListenOn, merge_mfargs(Opts, MFA)).
+
+merge_mfargs(Opts, MFA) ->
+    [{connection_mfargs, MFA} | proplists:delete(connection_mfargs, Opts)].
 
 %%--------------------------------------------------------------------
 %% Get/Set APIs
@@ -276,6 +325,14 @@ deny({Proto, ListenOn}, CIDR) when is_atom(Proto) ->
 %%--------------------------------------------------------------------
 %% Utils
 
+-spec start_mfargs(mfargs(), _Arg1, _Arg2) -> _Ret.
+start_mfargs(M, A1, A2) when is_atom(M) ->
+    M:start_link(A1, A2);
+start_mfargs({M, F}, A1, A2) when is_atom(M), is_atom(F) ->
+    M:F(A1, A2);
+start_mfargs({M, F, Args}, A1, A2) when is_atom(M), is_atom(F), is_list(Args) ->
+    erlang:apply(M, F, [A1, A2 | Args]).
+
 %% @doc Merge two options
 -spec(merge_opts(proplists:proplist(), proplists:proplist())
       -> proplists:proplist()).
@@ -300,6 +357,19 @@ merge_opt(udp_options, Opts1, Opts2) -> merge_opts(Opts1, Opts2);
 merge_opt(dtls_options, Opts1, Opts2) -> merge_opts(Opts1, Opts2);
 merge_opt(_, _Opt1, Opt2) -> Opt2.
 
+-spec changed_opts(proplists:proplist(), proplists:proplist())
+      -> proplists:proplist().
+changed_opts(Opts, OptsRef) ->
+    lists:filter(
+        fun(Opt) ->
+            [Name] = proplists:get_keys([Opt]),
+            Value = proplists:get_value(Name, [Opt]),
+            ValueRef = proplists:get_value(Name, OptsRef),
+            ValueRef =/= Value orelse ValueRef == undefined
+        end,
+        Opts
+    ).
+
 %% @doc Parse option.
 parse_opt(Options) ->
     parse_opt(Options, []).
diff --git a/src/esockd_connection_sup.erl b/src/esockd_connection_sup.erl
index bf8137c..395f3b1 100644
--- a/src/esockd_connection_sup.erl
+++ b/src/esockd_connection_sup.erl
@@ -18,9 +18,9 @@
 
 -behaviour(gen_server).
 
--import(proplists, [get_value/3]).
+-import(proplists, [get_value/3, get_value/2]).
 
--export([start_link/2, start_supervised/2, stop/1]).
+-export([start_link/1, start_supervised/1, stop/1]).
 
 -export([ start_connection/3
         , count_connections/1
@@ -67,16 +67,16 @@
         error_logger:error_msg("[~s] " ++ Format, [?MODULE | Args])).
 
 %% @doc Start connection supervisor.
--spec(start_link([esockd:option()], esockd:mfargs())
-      -> {ok, pid()} | ignore | {error, term()}).
-start_link(Opts, MFA) ->
-    gen_server:start_link(?MODULE, [Opts, MFA], []).
+-spec start_link([esockd:option()])
+      -> {ok, pid()} | ignore | {error, term()}.
+start_link(Opts) ->
+    gen_server:start_link(?MODULE, Opts, []).
 
--spec start_supervised(esockd:listener_ref(), esockd:mfargs())
+-spec start_supervised(esockd:listener_ref())
       -> {ok, pid()} | ignore | {error, term()}.
-start_supervised(ListenerRef, MFA) ->
+start_supervised(ListenerRef) ->
     Opts = esockd_server:get_listener_prop(ListenerRef, options),
-    case start_link(Opts, MFA) of
+    case start_link(Opts) of
         {ok, Pid} ->
             _ = esockd_server:set_listener_prop(ListenerRef, connection_sup, Pid),
             {ok, Pid};
@@ -113,14 +113,10 @@ start_connection(Sup, Sock, UpgradeFuns) ->
     end.
 
 %% @doc Start the connection process.
--spec(start_connection_proc(esockd:mfargs(), esockd_transport:socket())
-      -> {ok, pid()} | ignore | {error, term()}).
-start_connection_proc(M, Sock) when is_atom(M) ->
-    M:start_link(?TRANSPORT, Sock);
-start_connection_proc({M, F}, Sock) when is_atom(M), is_atom(F) ->
-    M:F(?TRANSPORT, Sock);
-start_connection_proc({M, F, Args}, Sock) when is_atom(M), is_atom(F), is_list(Args) ->
-    erlang:apply(M, F, [?TRANSPORT, Sock | Args]).
+-spec start_connection_proc(esockd:mfargs(), esockd_transport:socket())
+      -> {ok, pid()} | ignore | {error, term()}.
+start_connection_proc(MFA, Sock) ->
+    esockd:start_mfargs(MFA, ?TRANSPORT, Sock).
 
 -spec(count_connections(pid()) -> integer()).
 count_connections(Sup) ->
@@ -150,12 +146,13 @@ call(Sup, Req) ->
 %% gen_server callbacks
 %%--------------------------------------------------------------------
 
-init([Opts, MFA]) ->
+init(Opts) ->
     process_flag(trap_exit, true),
     Shutdown = get_value(shutdown, Opts, brutal_kill),
     MaxConns = get_value(max_connections, Opts, ?DEFAULT_MAX_CONNS),
     RawRules = get_value(access_rules, Opts, [{allow, all}]),
     AccessRules = [esockd_access:compile(Rule) || Rule <- RawRules],
+    MFA = get_value(connection_mfargs, Opts),
     {ok, #state{curr_connections = #{},
                 max_connections  = MaxConns,
                 access_rules     = AccessRules,
@@ -218,7 +215,8 @@ handle_call(get_options, _From, State) ->
     Options = [
         {shutdown, get_state_option(shutdown, State)},
         {max_connections, get_state_option(max_connections, State)},
-        {access_rules, get_state_option(access_rules, State)}
+        {access_rules, get_state_option(access_rules, State)},
+        {connection_mfargs, get_state_option(connection_mfargs, State)}
     ],
     {reply, Options, State};
 
@@ -280,7 +278,9 @@ get_state_option(max_connections, #state{max_connections = MaxConnections}) ->
 get_state_option(shutdown, #state{shutdown = Shutdown}) ->
     Shutdown;
 get_state_option(access_rules, #state{access_rules = Rules}) ->
-    [raw(Rule) || Rule <- Rules].
+    [raw(Rule) || Rule <- Rules];
+get_state_option(connection_mfargs, #state{mfargs = MFA}) ->
+    MFA.
 
 set_state_option({max_connections, MaxConns}, State) ->
     State#state{max_connections = MaxConns};
@@ -293,6 +293,8 @@ set_state_option({access_rules, Rules}, State) ->
     catch
         error:_Reason -> {error, bad_access_rules}
     end;
+set_state_option({connection_mfargs, MFA}, State) ->
+    State#state{mfargs = MFA};
 set_state_option(_, State) ->
     State.
 
diff --git a/src/esockd_dtls_listener.erl b/src/esockd_dtls_listener.erl
index 2e44b50..06c0718 100644
--- a/src/esockd_dtls_listener.erl
+++ b/src/esockd_dtls_listener.erl
@@ -44,10 +44,11 @@
           listen_on :: esockd:listen_on(),
           lsock     :: ssl:sslsocket(),
           laddr     :: inet:ip_address(),
-          lport     :: inet:port_number()
+          lport     :: inet:port_number(),
+          sockopts  :: [ssl:tls_server_option()]
          }).
 
--type option() :: {dtls_options, [gen_tcp:option()]}.
+-type option() :: {dtls_options, [gen_udp:option()]}.
 
 -define(DEFAULT_DTLS_OPTIONS,
         [{protocol, dtls},
@@ -95,16 +96,16 @@ init({Proto, ListenOn, Opts}) ->
     Port = port(ListenOn),
     process_flag(trap_exit, true),
     esockd_server:ensure_stats({Proto, ListenOn}),
-    SockOpts = merge_addr(ListenOn, dltsopts(Opts)),
+    SockOpts = merge_defaults(merge_addr(ListenOn, dltsopts(Opts))),
     %% Don't active the socket...
-    case ssl:listen(Port, esockd:merge_opts(?DEFAULT_DTLS_OPTIONS, SockOpts)) of
+    case ssl:listen(Port, SockOpts) of
     %%case ssl:listen(Port, [{active, false} | proplists:delete(active, SockOpts)]) of
         {ok, LSock} ->
             {ok, {LAddr, LPort}} = ssl:sockname(LSock),
             %%error_logger:info_msg("~s listen on ~s:~p with ~p acceptors.~n",
             %%                      [Proto, inet:ntoa(LAddr), LPort, AcceptorNum]),
-            {ok, #state{proto = Proto, listen_on = ListenOn,
-                        lsock = LSock, laddr = LAddr, lport = LPort}};
+            {ok, #state{proto = Proto, listen_on = ListenOn, lsock = LSock,
+                        laddr = LAddr, lport = LPort, sockopts = SockOpts}};
         {error, Reason} ->
             error_logger:error_msg("~s failed to listen on ~p - ~p (~s)",
                                    [Proto, Port, Reason, inet:format_error(Reason)]),
@@ -112,14 +113,22 @@ init({Proto, ListenOn, Opts}) ->
     end.
 
 dltsopts(Opts) ->
-    proplists:delete(
-     handshake_timeout,
-     proplists:get_value(dtls_options, Opts, [])
-    ).
+    %% Filter out `esockd:ssl_custom_option()`, otherwise DTLS listener will
+    %% fail to start.
+    DTLSOpts = lists:foldl(
+        fun proplists:delete/2,
+        proplists:get_value(dtls_options, Opts, []),
+        [handshake_timeout, gc_after_handshake]
+    ),
+    SockOpts = proplists:get_value(udp_options, Opts, []),
+    SockOpts ++ DTLSOpts.
 
 port(Port) when is_integer(Port) -> Port;
 port({_Addr, Port}) -> Port.
 
+merge_defaults(SockOpts) ->
+    esockd:merge_opts(?DEFAULT_DTLS_OPTIONS, SockOpts).
+
 merge_addr(Port, SockOpts) when is_integer(Port) ->
     SockOpts;
 merge_addr({Addr, _Port}, SockOpts) ->
@@ -134,10 +143,13 @@ handle_call(get_state, _From, State = #state{lsock = LSock, lport = LPort}) ->
             ],
     {reply, Reply, State};
 
-handle_call({set_options, Opts}, _From, State = #state{lsock = LSock}) ->
-    case ssl:setopts(LSock, dltsopts(Opts)) of
+handle_call({set_options, Opts}, _From, State = #state{lsock = LSock, sockopts = SockOpts}) ->
+    SockOptsIn = dltsopts(Opts),
+    SockOptsChanged = esockd:changed_opts(SockOptsIn, SockOpts),
+    case ssl:setopts(LSock, SockOptsChanged) of
         ok ->
-            {reply, ok, State};
+            SockOptsMerged = esockd:merge_opts(SockOpts, SockOptsChanged),
+            {reply, ok, State#state{sockopts = SockOptsMerged}};
         Error = {error, _} ->
             %% Setting dTLS options on listening socket always succeeds,
             %% even if the options are invalid.
diff --git a/src/esockd_listener.erl b/src/esockd_listener.erl
index eda34d0..ed775ed 100644
--- a/src/esockd_listener.erl
+++ b/src/esockd_listener.erl
@@ -44,7 +44,8 @@
           listen_on :: esockd:listen_on(),
           lsock     :: inet:socket(),
           laddr     :: inet:ip_address(),
-          lport     :: inet:port_number()
+          lport     :: inet:port_number(),
+          sockopts  :: [gen_tcp:listen_option()]
          }).
 
 -type option() :: {tcp_options, [gen_tcp:option()]}.
@@ -97,14 +98,14 @@ init({Proto, ListenOn, Opts}) ->
     Port = port(ListenOn),
     process_flag(trap_exit, true),
     esockd_server:ensure_stats({Proto, ListenOn}),
-    SockOpts = merge_addr(ListenOn, sockopts(Opts)),
-    case esockd_transport:listen(Port, esockd:merge_opts(?DEFAULT_TCP_OPTIONS, SockOpts)) of
+    SockOpts = merge_addr(ListenOn, merge_defaults(sockopts(Opts))),
+    case esockd_transport:listen(Port, SockOpts) of
         {ok, LSock} ->
             {ok, {LAddr, LPort}} = inet:sockname(LSock),
             %%error_logger:info_msg("~s listen on ~s:~p with ~p acceptors.~n",
             %%                      [Proto, inet:ntoa(LAddr), LPort, AcceptorNum]),
-            {ok, #state{proto = Proto, listen_on = ListenOn,
-                        lsock = LSock, laddr = LAddr, lport = LPort}};
+            {ok, #state{proto = Proto, listen_on = ListenOn, lsock = LSock,
+                        laddr = LAddr, lport = LPort, sockopts = SockOpts}};
         {error, Reason} ->
             error_logger:error_msg("~s failed to listen on ~p - ~p (~s)",
                                    [Proto, Port, Reason, inet:format_error(Reason)]),
@@ -116,6 +117,9 @@ sockopts(Opts) ->
     SockOpts = proplists:get_value(tcp_options, Opts, []),
     [{active, false} | proplists:delete(active, SockOpts)].
 
+merge_defaults(SockOpts) ->
+    esockd:merge_opts(?DEFAULT_TCP_OPTIONS, SockOpts).
+
 port(Port) when is_integer(Port) -> Port;
 port({_Addr, Port}) -> Port.
 
@@ -136,10 +140,13 @@ handle_call(get_state, _From, State = #state{lsock = LSock, lport = LPort}) ->
             ],
     {reply, Reply, State};
 
-handle_call({set_options, Opts}, _From, State = #state{lsock = LSock}) ->
-    case inet:setopts(LSock, sockopts(Opts)) of
+handle_call({set_options, Opts}, _From, State = #state{lsock = LSock, sockopts = SockOpts}) ->
+    SockOptsIn = sockopts(Opts),
+    SockOptsChanged = esockd:changed_opts(SockOptsIn, SockOpts),
+    case inet:setopts(LSock, SockOptsChanged) of
         ok ->
-            {reply, ok, State};
+            SockOptsMerged = esockd:merge_opts(SockOpts, SockOptsChanged),
+            {reply, ok, State#state{sockopts = SockOptsMerged}};
         Error = {error, _} ->
             {reply, Error, State}
     end;
diff --git a/src/esockd_listener_sup.erl b/src/esockd_listener_sup.erl
index 46e9dba..efd3cad 100644
--- a/src/esockd_listener_sup.erl
+++ b/src/esockd_listener_sup.erl
@@ -20,8 +20,7 @@
 
 -include("esockd.hrl").
 
--export([ start_link/5
-        , start_link/3
+-export([ start_link/2
         , listener/1
         , acceptor_sup/1
         , connection_sup/1
@@ -56,30 +55,16 @@
         , start_acceptors/1
         ]).
 
--type listen_type() :: tcp | dtls.
-
 %%--------------------------------------------------------------------
 %% APIs
 %%--------------------------------------------------------------------
 
 %% @doc Start listener supervisor
--spec start_link(listen_type(), atom(), esockd:listen_on(), [esockd:option()], esockd:mfargs())
-      -> {ok, pid()} | {error, term()}.
-start_link(Type, Proto, ListenOn, Opts, MFA) ->
-    %% NOTE
-    %% `Opts` are still part of the childspec, which means if whole listener supervisor
-    %% restarts, any changes done through `set_options` will be lost.
-    ListenerRef = {Proto, ListenOn},
-    _ = esockd_server:set_listener_prop(ListenerRef, type, Type),
-    _ = esockd_server:set_listener_prop(ListenerRef, options, Opts),
-    supervisor:start_link(?MODULE, {ListenerRef, MFA}).
-
-%% @doc Start listener supervisor
--spec start_link(atom(), esockd:listen_on(), esockd:mfargs())
+-spec start_link(atom(), esockd:listen_on())
       -> {ok, pid()} | {error, term()}.
-start_link(Proto, ListenOn, MFA) ->
+start_link(Proto, ListenOn) ->
     ListenerRef = {Proto, ListenOn},
-    supervisor:start_link(?MODULE, {ListenerRef, MFA}).
+    supervisor:start_link(?MODULE, ListenerRef).
 
 %% @doc Get listener.
 -spec(listener(pid()) -> {module(), pid()}).
@@ -125,7 +110,7 @@ set_options(ListenerRef, Sup, Opts) ->
             %% Restore previous options
             _ = esockd_server:set_listener_prop(ListenerRef, options, OptsWas),
             ok = esockd_connection_sup:set_options(ConnSup, OptsWas),
-            ok = Listener:set_options(ListenerPid, OptsWas),
+            %% Listener has failed to set options, no need to restore
             Error
     end,
     ok = restart_acceptor_sup(ListenerRef, Sup),
@@ -181,9 +166,9 @@ deny(Sup, CIDR) ->
 %% Supervisor callbacks
 %%--------------------------------------------------------------------
 
-init({ListenerRef, MFA}) ->
+init(ListenerRef) ->
     ConnSup = #{id => connection_sup,
-                start => {esockd_connection_sup, start_supervised, [ListenerRef, MFA]},
+                start => {esockd_connection_sup, start_supervised, [ListenerRef]},
                 restart => transient,
                 shutdown => infinity,
                 type => supervisor,
diff --git a/src/esockd_sup.erl b/src/esockd_sup.erl
index 29291f2..5565a58 100644
--- a/src/esockd_sup.erl
+++ b/src/esockd_sup.erl
@@ -22,7 +22,7 @@
 
 -export([child_id/2]).
 
--export([ start_listener/4
+-export([ start_child/1
         , stop_listener/2
         , restart_listener/2
         ]).
@@ -32,10 +32,9 @@
         , listener_and_module/1
         ]).
 
--export([ child_spec/4
-        , udp_child_spec/4
-        , dtls_child_spec/4
-        , start_child/1
+-export([ child_spec/3
+        , udp_child_spec/3
+        , dtls_child_spec/3
         ]).
 
 %% supervisor callback
@@ -49,42 +48,37 @@
 start_link() ->
     supervisor:start_link({local, ?MODULE}, ?MODULE, []).
 
--spec(start_listener(atom(), esockd:listen_on(), [esockd:option()], esockd:mfargs())
-      -> {ok, pid()} | {error, term()}).
-start_listener(Proto, ListenOn, Opts, MFA) ->
-    start_child(child_spec(Proto, ListenOn, Opts, MFA)).
-
--spec(child_spec(atom(), esockd:listen_on(), [esockd:option()], esockd:mfargs())
-      -> supervisor:child_spec()).
-child_spec(Proto, ListenOn, Opts, MFA) when is_atom(Proto) ->
+-spec child_spec(atom(), esockd:listen_on(), [esockd:option()])
+      -> supervisor:child_spec().
+child_spec(Proto, ListenOn, Opts) when is_atom(Proto) ->
     ListenerRef = {Proto, ListenOn},
     _ = esockd_server:set_listener_prop(ListenerRef, type, tcp),
     _ = esockd_server:set_listener_prop(ListenerRef, options, Opts),    
     #{id => child_id(Proto, ListenOn),
-      start => {esockd_listener_sup, start_link, [Proto, ListenOn, MFA]},
+      start => {esockd_listener_sup, start_link, [Proto, ListenOn]},
       restart => transient,
       shutdown => infinity,
       type => supervisor,
       modules => [esockd_listener_sup]}.
 
--spec(udp_child_spec(atom(), esockd:listen_on(), [esockd:option()], esockd:mfargs())
-      -> supervisor:child_spec()).
-udp_child_spec(Proto, Port, Opts, MFA) when is_atom(Proto) ->
+-spec udp_child_spec(atom(), esockd:listen_on(), [esockd:option()])
+      -> supervisor:child_spec().
+udp_child_spec(Proto, Port, Opts) when is_atom(Proto) ->
     #{id => child_id(Proto, Port),
-      start => {esockd_udp, server, [Proto, Port, Opts, MFA]},
+      start => {esockd_udp, server, [Proto, Port, Opts]},
       restart => transient,
       shutdown => 5000,
       type => worker,
       modules => [esockd_udp]}.
 
--spec(dtls_child_spec(atom(), esockd:listen_on(), [esockd:option()], esockd:mfargs())
-      -> supervisor:child_spec()).
-dtls_child_spec(Proto, Port, Opts, MFA) when is_atom(Proto) ->
+-spec dtls_child_spec(atom(), esockd:listen_on(), [esockd:option()])
+      -> supervisor:child_spec().
+dtls_child_spec(Proto, Port, Opts) when is_atom(Proto) ->
     ListenerRef = {Proto, Port},
     _ = esockd_server:set_listener_prop(ListenerRef, type, dtls),
     _ = esockd_server:set_listener_prop(ListenerRef, options, Opts),    
     #{id => child_id(Proto, Port),
-      start => {esockd_listener_sup, start_link, [Proto, Port, MFA]},
+      start => {esockd_listener_sup, start_link, [Proto, Port]},
       restart => transient,
       shutdown => infinity,
       type => supervisor,
diff --git a/src/esockd_udp.erl b/src/esockd_udp.erl
index 7f75e27..465510c 100644
--- a/src/esockd_udp.erl
+++ b/src/esockd_udp.erl
@@ -20,7 +20,7 @@
 
 -import(esockd_listener_sup, [conn_rate_limiter/1, conn_limiter_opts/2, conn_limiter_opt/2]).
 
--export([ server/4
+-export([ server/3
         , count_peers/1
         , stop/1
         ]).
@@ -79,10 +79,10 @@
 %% API
 %%--------------------------------------------------------------------
 
--spec(server(atom(), esockd:listen_on(), [gen_udp:option()], mfa())
+-spec(server(atom(), esockd:listen_on(), [esockd:option()])
       -> {ok, pid()} | {error, term()}).
-server(Proto, ListenOn, Opts, MFA) ->
-    gen_server:start_link(?MODULE, [Proto, ListenOn, Opts, MFA], []).
+server(Proto, ListenOn, Opts) ->
+    gen_server:start_link(?MODULE, [Proto, ListenOn, Opts], []).
 
 resolve_addr(Port, SockOpts) when is_integer(Port) ->
     SockOpts;
@@ -153,10 +153,11 @@ deny(Pid, CIDR) ->
 %% gen_server callbacks
 %%--------------------------------------------------------------------
 
-init([Proto, ListenOn, Opts, MFA]) ->
+init([Proto, ListenOn, Opts]) ->
     process_flag(trap_exit, true),
     put(incoming_peers, 0),
 
+    MFA = proplists:get_value(connection_mfargs, Opts),
     RawRules = proplists:get_value(access_rules, Opts, [{allow, all}]),
     AccessRules = [esockd_access:compile(Rule) || Rule <- RawRules],
 
@@ -346,8 +347,8 @@ should_throttle(#state{max_peers = infinity}) -> false;
 should_throttle(#state{max_peers = MaxLimit, peers = Peers}) ->
     (maps:size(Peers) div 2) > MaxLimit.
 
-start_channel(Transport, Peer, #state{mfa = {M, F, Args}}) ->
-    erlang:apply(M, F, [Transport, Peer | Args]).
+start_channel(Transport, Peer, #state{mfa = MFA}) ->
+    esockd:start_mfargs(MFA, Transport, Peer).
 
 activate_sock(State = #state{sock = Sock}) ->
     ok = inet:setopts(Sock, [{active, ?ACTIVE_N}]), State.
diff --git a/test/const_server.erl b/test/const_server.erl
new file mode 100644
index 0000000..6e666d8
--- /dev/null
+++ b/test/const_server.erl
@@ -0,0 +1,45 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2020 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(const_server).
+
+-export([start_link/3]).
+
+%% Callbacks
+-export([init/3, loop/3]).
+
+start_link(Transport, RawSock, Resp) ->
+	{ok, spawn_link(?MODULE, init, [Transport, RawSock, Resp])}.
+
+init(Transport, RawSock, Resp) ->
+    case Transport:wait(RawSock) of
+        {ok, Sock} ->
+            loop(Transport, Sock, Resp);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+loop(Transport, Sock, Resp) ->
+	case Transport:recv(Sock, 0) of
+        {ok, _Data} ->
+            Transport:send(Sock, Resp),
+            loop(Transport, Sock, Resp);
+        {shutdown, Reason} ->
+            exit({shutdown, Reason});
+        {error, Reason} ->
+            exit({shutdown, Reason})
+	end.
+
diff --git a/test/esockd_SUITE.erl b/test/esockd_SUITE.erl
index edb7f1c..62e474d 100644
--- a/test/esockd_SUITE.erl
+++ b/test/esockd_SUITE.erl
@@ -33,16 +33,16 @@ end_per_suite(_Config) ->
     application:stop(esockd).
 
 t_open_close(_) ->
-    {ok, _LSup} = esockd:open(echo, {"127.0.0.1", 3000}, [binary, {packet, raw}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, {"127.0.0.1", 3000},
+                              [binary, {packet, raw}, {connection_mfargs, echo_server}]),
     {ok, Sock} = gen_tcp:connect("127.0.0.1", 3000, [binary, {active, false}]),
     ok = gen_tcp:send(Sock, <<"Hello">>),
     {ok, <<"Hello">>} = gen_tcp:recv(Sock, 0),
     ok = esockd:close(echo, {"127.0.0.1", 3000}).
 
 t_reopen(_) ->
-    {ok, _LSup} = esockd:open(echo, {"127.0.0.1", 3000}, [binary, {packet, raw}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, {"127.0.0.1", 3000},
+                              [binary, {packet, raw}, {connection_mfargs, echo_server}]),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 3000, [{active, false}]),
     ok = gen_tcp:send(Sock1, <<"Hello">>),
     timer:sleep(10),
@@ -53,8 +53,9 @@ t_reopen(_) ->
     ok = esockd:close(echo, {"127.0.0.1", 3000}).
 
 t_reopen_1(_) ->
-    {ok, _LSup} = esockd:open(echo, 7000, [{max_connections, 4}, {acceptors, 4}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000,
+                              [{max_connections, 4}, {acceptors, 4},
+                               {connection_mfargs, echo_server}]),
     timer:sleep(10),
     ok = esockd:reopen({echo, 7000}),
     ?assertEqual(4, esockd:get_max_connections({echo, 7000})),
@@ -63,7 +64,8 @@ t_reopen_1(_) ->
 
 t_reopen_fail(_) ->
     LPort = 4001,
-    {ok, _LSup} = esockd:open(echo, LPort, [{acceptors, 4}], {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, LPort,
+                              [{acceptors, 4}, {connection_mfargs, {echo_server, start_link}}]),
     {error, not_found} = esockd:reopen({echo, 5000}),
     ?assertEqual(4, esockd:get_acceptors({echo, LPort})),
     {ok, Sock} = gen_tcp:connect({127,0,0,1}, LPort, [binary, {active, false}]),
@@ -72,14 +74,17 @@ t_reopen_fail(_) ->
     ok = esockd:close(echo, LPort).
 
 t_open_udp(_) ->
-    {ok, _} = esockd:open_udp(echo, 5678, [], {udp_echo_server, start_link, []}),
+    {ok, _} = esockd:open_udp(echo, 5678,
+                              [{connection_mfargs, {udp_echo_server, start_link}}]),
     {ok, Sock} = gen_udp:open(0, [binary, {active, false}]),
     ok = gen_udp:send(Sock, {127,0,0,1}, 5678, <<"Hi">>),
     {ok, {_Addr, 5678, <<"Hi">>}} = gen_udp:recv(Sock, 0),
     ok = esockd:close(echo, 5678).
 
 t_udp_child_spec(_) ->
-    Spec = esockd:udp_child_spec(echo, 5000, [], {udp_echo_server, start_link, []}),
+    MFA = {udp_echo_server, start_link, []},
+    Spec = esockd:udp_child_spec(echo, 5000, [{connection_mfargs, MFA}]),
+    Spec = esockd:udp_child_spec(echo, 5000, [], MFA),
     #{id := {listener_sup,{echo,5000}},
       modules := [esockd_udp],
       restart := transient,
@@ -88,14 +93,13 @@ t_udp_child_spec(_) ->
      } = Spec.
 
 t_open_dtls(Config) ->
-    DtlsOpts = [{mode, binary},
-                {reuseaddr, true},
-                {certfile, esockd_ct:certfile(Config)},
+    DtlsOpts = [{certfile, esockd_ct:certfile(Config)},
                 {keyfile,  esockd_ct:keyfile(Config)},
                 {verify, verify_none}
                ],
-    {ok, _} = esockd:open_dtls(echo, 5000, [{dtls_options, DtlsOpts}],
-                               {dtls_echo_server, start_link, []}),
+    {ok, _} = esockd:open_dtls(echo, 5000,
+                               [{dtls_options, DtlsOpts},
+                                {connection_mfargs, dtls_echo_server}]),
     {ok, Sock} = ssl:connect({127,0,0,1}, 5000, [binary,
                                                  {protocol, dtls},
                                                  {active, false},
@@ -107,7 +111,9 @@ t_open_dtls(Config) ->
     ok = esockd:close(echo, 5000).
 
 t_dtls_child_spec(_) ->
-    Spec = esockd:dtls_child_spec(echo, 8883, [], {udp_echo_server, start_link, []}),
+    MFA = {udp_echo_server, start_link, []},
+    Spec = esockd:dtls_child_spec(echo, 8883, [{connection_mfargs, MFA}]),
+    Spec = esockd:dtls_child_spec(echo, 8883, [], MFA),
      #{id := {listener_sup,{echo,8883}},
        modules := [esockd_listener_sup],
        restart := transient,
@@ -116,7 +122,9 @@ t_dtls_child_spec(_) ->
       } = Spec.
 
 t_child_spec(_) ->
-    Spec = esockd:child_spec(echo, 5000, [], {echo_server, start_link, []}),
+    MFA = {udp_echo_server, start_link, []},
+    Spec = esockd:child_spec(echo, 5000, [{connection_mfargs, MFA}]),
+    Spec = esockd:child_spec(echo, 5000, [], MFA),
     #{id := {listener_sup, {echo,5000}},
       modules := [esockd_listener_sup],
       restart := transient,
@@ -125,7 +133,7 @@ t_child_spec(_) ->
      } = Spec.
 
 t_listeners(_) ->
-    {ok, LSup} = esockd:open(echo, 6000, [], {echo_server, start_link, []}),
+    {ok, LSup} = esockd:open(echo, 6000, [{connection_mfargs, echo_server}]),
     [{{echo, 6000}, LSup}] = esockd:listeners(),
     ?assertEqual(LSup, esockd:listener({echo, 6000})),
     ok = esockd:close(echo, 6000),
@@ -133,7 +141,7 @@ t_listeners(_) ->
     ?assertException(error, not_found, esockd:listener({echo, 6000})).
 
 t_get_stats(_) ->
-    {ok, _LSup} = esockd:open(echo, 6000, [], {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 6000, [{connection_mfargs, echo_server}]),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 6000, [{active, false}]),
     {ok, Sock2} = gen_tcp:connect("127.0.0.1", 6000, [{active, false}]),
     timer:sleep(10),
@@ -145,44 +153,50 @@ t_get_stats(_) ->
     ok = esockd:close(echo, 6000).
 
 t_get_options(_) ->
-    {ok, _LSup} = esockd:open(echo, 6000, [{acceptors, 4}],
-                              {echo_server, start_link, []}),
-    [{acceptors, 4}] = esockd:get_options({echo, 6000}),
+    {ok, _LSup} = esockd:open(echo, 6000,
+                              [{acceptors, 4},
+                               {connection_mfargs, {echo_server, start_link}}]),
+    [{acceptors, 4},
+     {connection_mfargs, {echo_server, start_link}}] = esockd:get_options({echo, 6000}),
     ok = esockd:close(echo, 6000),
     ?assertException(error, not_found, esockd:get_options({echo, 6000})),
 
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 6000, [{acceptors, 4}],
-                               {dtls_echo_server, start_link, []}),
-    [{acceptors, 4}] = esockd:get_options({dtls_echo, 6000}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 6000,
+                                    [{acceptors, 4},
+                                     {connection_mfargs, {dtls_echo_server, start_link}}]),
+    [{acceptors, 4},
+     {connection_mfargs, {dtls_echo_server, start_link}}] = esockd:get_options({dtls_echo, 6000}),
     ok = esockd:close(dtls_echo, 6000),
     ?assertException(error, not_found, esockd:get_options({dtls_echo, 6000})),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 6000, [{acceptors, 4}],
-                               {udp_echo_server, start_link, []}),
-    [{acceptors, 4}] = esockd:get_options({udp_echo, 6000}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 6000,
+                                   [{acceptors, 4},
+                                    {connection_mfargs, {udp_echo_server, start_link, []}}]),
+    [{acceptors, 4},
+     {connection_mfargs, {udp_echo_server, start_link, []}}] = esockd:get_options({udp_echo, 6000}),
     ok = esockd:close(udp_echo, 6000),
     ?assertException(error, not_found, esockd:get_options({udp_echo, 6000})).
 
 t_get_acceptors(_) ->
-    {ok, _LSup} = esockd:open(echo, 6000, [{acceptors, 4}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 6000,
+                              [{acceptors, 4}, {connection_mfargs, echo_server}]),
     ?assertEqual(4, esockd:get_acceptors({echo, 6000})),
     ok = esockd:close(echo, 6000),
 
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 6000, [{acceptors, 4}],
-                               {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 6000,
+                                    [{acceptors, 4}, {connection_mfargs, dtls_echo_server}]),
     ?assertEqual(4, esockd:get_acceptors({dtls_echo, 6000})),
     ok = esockd:close(dtls_echo, 6000),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 6000, [{acceptors, 4}],
-                               {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 6000,
+                                   [{acceptors, 4}, {connection_mfargs, udp_echo_server}]),
     %% fixed 1
     ?assertEqual(1, esockd:get_acceptors({udp_echo, 6000})),
     ok = esockd:close(udp_echo, 6000).
 
 t_get_set_max_connections(_) ->
-    {ok, _LSup} = esockd:open(echo, 7000, [{max_connections, 4}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000,
+                              [{max_connections, 4}, {connection_mfargs, echo_server}]),
     ?assertEqual(4, esockd:get_max_connections({echo, 7000})),
     {ok, _Sock1} = gen_tcp:connect("localhost", 7000, [{active, false}]),
     {ok, _Sock2} = gen_tcp:connect("localhost", 7000, [{active, false}]),
@@ -192,15 +206,17 @@ t_get_set_max_connections(_) ->
     ?assertEqual({error, closed}, gen_tcp:recv(Sock3, 0)),
     ok = esockd:close(echo, 7000),
 
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{max_connections, 4}],
-                               {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000,
+                                    [{max_connections, 4},
+                                     {connection_mfargs, dtls_echo_server}]),
     ?assertEqual(4, esockd:get_max_connections({dtls_echo, 7000})),
     esockd:set_max_connections({dtls_echo, 7000}, 16),
     ?assertEqual(16, esockd:get_max_connections({dtls_echo, 7000})),
     ok = esockd:close(dtls_echo, 7000),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 7000, [{max_connections, 4}],
-                               {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 7000,
+                                   [{max_connections, 4},
+                                    {connection_mfargs, udp_echo_server}]),
     ?assertEqual(4, esockd:get_max_connections({udp_echo, 7000})),
     esockd:set_max_connections({udp_echo, 7000}, 16),
     ?assertEqual(16, esockd:get_max_connections({udp_echo, 7000})),
@@ -208,8 +224,8 @@ t_get_set_max_connections(_) ->
 
 t_get_set_max_conn_rate(_) ->
     LimiterOpt = #{module => esockd_limiter, capacity => 100, interval => 1},
-    {ok, _LSup} = esockd:open(echo, 7000, [{limiter, LimiterOpt}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000, 
+                              [{limiter, LimiterOpt}, {connection_mfargs, echo_server}]),
     ?assertEqual({100, 1}, esockd:get_max_conn_rate({echo, 7000})),
     esockd:set_max_conn_rate({echo, 7000}, LimiterOpt#{capacity := 50, interval := 2}),
     ?assertEqual({50, 2}, esockd:get_max_conn_rate({echo, 7000})),
@@ -217,16 +233,18 @@ t_get_set_max_conn_rate(_) ->
     ?assertException(error, not_found, esockd:get_max_conn_rate({echo, 7000})),
 
 
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{limiter, LimiterOpt}],
-                                    {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000,
+                                    [{limiter, LimiterOpt},
+                                     {connection_mfargs, dtls_echo_server}]),
     ?assertEqual({100, 1}, esockd:get_max_conn_rate({dtls_echo, 7000})),
     esockd:set_max_conn_rate({dtls_echo, 7000}, LimiterOpt#{capacity := 50, interval := 2}),
     ?assertEqual({50, 2}, esockd:get_max_conn_rate({dtls_echo, 7000})),
     ok = esockd:close(dtls_echo, 7000),
     ?assertException(error, not_found, esockd:get_max_conn_rate({dtls_echo, 7000})),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 7000, [{limiter, LimiterOpt}],
-                                   {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 7000,
+                                   [{limiter, LimiterOpt},
+                                    {connection_mfargs, udp_echo_server}]),
     ?assertEqual({100, 1}, esockd:get_max_conn_rate({udp_echo, 7000})),
     esockd:set_max_conn_rate({udp_echo, 7000}, LimiterOpt#{capacity := 50, interval := 2}),
     ?assertEqual({50, 2}, esockd:get_max_conn_rate({udp_echo, 7000})),
@@ -234,7 +252,7 @@ t_get_set_max_conn_rate(_) ->
     ?assertException(error, not_found, esockd:get_max_conn_rate({udp_echo, 7000})).
 
 t_get_current_connections(Config) ->
-    {ok, _LSup} = esockd:open(echo, 7000, [], {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000, [{connection_mfargs, {echo_server, start_link, []}}]),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 7000, [{active, false}]),
     {ok, Sock2} = gen_tcp:connect("127.0.0.1", 7000, [{active, false}]),
     timer:sleep(10),
@@ -245,14 +263,15 @@ t_get_current_connections(Config) ->
     ?assertEqual(0, esockd:get_current_connections({echo, 7000})),
     ok = esockd:close(echo, 7000),
 
-    DtlsOpts = [{mode, binary},
-                {reuseaddr, true},
-                {certfile, esockd_ct:certfile(Config)},
+    UdpOpts = [{mode, binary}, {reuseaddr, true}],
+    DtlsOpts = [{certfile, esockd_ct:certfile(Config)},
                 {keyfile, esockd_ct:keyfile(Config)},
                 {verify, verify_none}
                ],
     ClientOpts = [binary, {protocol, dtls}, {verify, verify_none}],
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{dtls_options, DtlsOpts}], {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000,
+                                    [{dtls_options, DtlsOpts}, {udp_options, UdpOpts},
+                                     {connection_mfargs, dtls_echo_server}]),
     {ok, DtlsSock1} = ssl:connect({127,0,0,1}, 7000, ClientOpts, 5000),
     {ok, DtlsSock2} = ssl:connect({127,0,0,1}, 7000, ClientOpts, 5000),
     timer:sleep(10),
@@ -261,7 +280,7 @@ t_get_current_connections(Config) ->
     ok = ssl:close(DtlsSock2),
     ok = esockd:close(dtls_echo, 7000),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 7001, [], {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 7001, [{connection_mfargs, udp_echo_server}]),
     {ok, UdpSock1} = gen_udp:open(0, [binary, {active, false}]),
     {ok, UdpSock2} = gen_udp:open(0, [binary, {active, false}]),
     gen_udp:send(UdpSock1, {127,0,0,1}, 7001, <<"test">>),
@@ -273,7 +292,7 @@ t_get_current_connections(Config) ->
     ok = esockd:close(udp_echo, 7001).
 
 t_get_shutdown_count(Config) ->
-    {ok, _LSup} = esockd:open(echo, 7000, [], {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000, [{connection_mfargs, echo_server}]),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 7000, [{active, false}]),
     {ok, Sock2} = gen_tcp:connect("127.0.0.1", 7000, [{active, false}]),
     ok = gen_tcp:close(Sock1),
@@ -282,14 +301,15 @@ t_get_shutdown_count(Config) ->
     ?assertEqual([{closed, 2}], esockd:get_shutdown_count({echo, 7000})),
     ok = esockd:close(echo, 7000),
 
-    DtlsOpts = [{mode, binary},
-                {reuseaddr, true},
-                {certfile, esockd_ct:certfile(Config)},
+    UdpOpts = [{mode, binary}, {reuseaddr, true}],
+    DtlsOpts = [{certfile, esockd_ct:certfile(Config)},
                 {keyfile, esockd_ct:keyfile(Config)},
                 {verify, verify_none}
                ],
     ClientOpts = [binary, {protocol, dtls}, {verify, verify_none}],
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{dtls_options, DtlsOpts}], {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000,
+                                    [{dtls_options, DtlsOpts}, {udp_options, UdpOpts},
+                                     {connection_mfargs, dtls_echo_server}]),
     {ok, DtlsSock1} = ssl:connect({127,0,0,1}, 7000, ClientOpts, 5000),
     {ok, DtlsSock2} = ssl:connect({127,0,0,1}, 7000, ClientOpts, 5000),
     ok = ssl:close(DtlsSock1),
@@ -298,7 +318,7 @@ t_get_shutdown_count(Config) ->
     ?assertEqual([], esockd:get_shutdown_count({dtls_echo, 7000})),
     ok = esockd:close(dtls_echo, 7000),
 
-    {ok, _LSup2} = esockd:open_udp(udp_echo, 7001, [], {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_udp(udp_echo, 7001, [{connection_mfargs, udp_echo_server}]),
     {ok, UdpSock1} = gen_udp:open(0, [binary, {active, false}]),
     {ok, UdpSock2} = gen_udp:open(0, [binary, {active, false}]),
     gen_udp:send(UdpSock1, {127,0,0,1}, 7001, <<"test">>),
@@ -310,22 +330,42 @@ t_get_shutdown_count(Config) ->
     ok = esockd:close(udp_echo, 7001).
 
 t_update_options(_) ->
-    {ok, _LSup} = esockd:open(echo, 6000, [{acceptors, 4}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 6000,
+                              [{acceptors, 4},
+                               {tcp_options, [{backlog, 128}]},
+                               {connection_mfargs, echo_server}]),
     ?assertEqual(4, esockd:get_acceptors({echo, 6000})),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 6000, [binary, {active, false}]),
-    ok = esockd:set_options({echo, 6000}, [{acceptors, 16}, tune_buffer]),
+    %% Backlog size can not be changed
+    ?assertEqual(
+        {error, einval},
+        esockd:set_options({echo, 6000},
+                            [{acceptors, 8},
+                             {tcp_options, [{backlog, 256}]}])
+    ),
+    %% Number of acceptors haven't changed
+    ?assertEqual(4, esockd:get_acceptors({echo, 6000})),
+    %% Other TCP options are changeable
+    ?assertEqual(
+        ok,
+        esockd:set_options({echo, 6000},
+                           [{acceptors, 16},
+                            tune_buffer,
+                            {tcp_options, [{send_timeout_close, false}]},
+                            {connection_mfargs, {const_server, start_link, [<<"HEY">>]}}])
+    ),
     {ok, Sock2} = gen_tcp:connect("127.0.0.1", 6000, [binary, {active, false}]),
     ?assertEqual(16, esockd:get_acceptors({echo, 6000})),
+    %% Sockets should still be alive
     ok = gen_tcp:send(Sock1, <<"Sock1">>),
     {ok, <<"Sock1">>} = gen_tcp:recv(Sock1, 0),
     ok = gen_tcp:send(Sock2, <<"Sock2">>),
-    {ok, <<"Sock2">>} = gen_tcp:recv(Sock2, 0),
+    {ok, <<"HEY">>} = gen_tcp:recv(Sock2, 0),
     ok = esockd:close(echo, 6000).
 
 t_update_options_error(_) ->
-    {ok, _LSup} = esockd:open(echo, 6000, [{acceptors, 4}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 6000,
+                              [{acceptors, 4}, {connection_mfargs, echo_server}]),
     ?assertEqual(4, esockd:get_acceptors({echo, 6000})),
     {ok, Sock1} = gen_tcp:connect("127.0.0.1", 6000, [binary, {active, false}]),
     ?assertEqual( {error, bad_access_rules}
@@ -360,8 +400,8 @@ t_update_tls_options(Config) ->
                     , {cacertfile, esockd_ct:cacertfile(Config)}
                     , {customize_hostname_check, [{match_fun, fun(_, _) -> true end}]}
                     ],
-    {ok, _LSup} = esockd:open(echo_tls, LPort, [{ssl_options, SslOpts1}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo_tls, LPort,
+                              [{ssl_options, SslOpts1}, {connection_mfargs, echo_server}]),
     {ok, Sock1} = ssl:connect("localhost", LPort, ClientSslOpts, 1000),
 
     ok = esockd:set_options({echo_tls, LPort}, [{ssl_options, [{verify, verify_peer}]}]),
@@ -386,8 +426,7 @@ t_update_tls_options(Config) ->
 
 t_allow_deny(_) ->
     AccessRules = [{allow, "192.168.1.0/24"}],
-    {ok, _LSup} = esockd:open(echo, 7000, [{access_rules, AccessRules}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(echo, 7000, [{access_rules, AccessRules}]),
     ?assertEqual([{allow, "192.168.1.0/24"}], esockd:get_access_rules({echo, 7000})),
     ok = esockd:allow({echo, 7000}, "10.10.0.0/16"),
     ?assertEqual([{allow, "10.10.0.0/16"},
@@ -402,8 +441,7 @@ t_allow_deny(_) ->
 
     %% dtls
 
-    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{access_rules, AccessRules}],
-                                    {dtls_echo_server, start_link, []}),
+    {ok, _LSup1} = esockd:open_dtls(dtls_echo, 7000, [{access_rules, AccessRules}]),
     ?assertEqual([{allow, "192.168.1.0/24"}], esockd:get_access_rules({dtls_echo, 7000})),
     ok = esockd:allow({dtls_echo, 7000}, "10.10.0.0/16"),
     ?assertEqual([{allow, "10.10.0.0/16"},
@@ -418,8 +456,7 @@ t_allow_deny(_) ->
 
     %% udp
 
-    {ok, _LSup2} = esockd:open_dtls(udp_echo, 7001, [{access_rules, AccessRules}],
-                                    {udp_echo_server, start_link, []}),
+    {ok, _LSup2} = esockd:open_dtls(udp_echo, 7001, [{access_rules, AccessRules}]),
     ?assertEqual([{allow, "192.168.1.0/24"}], esockd:get_access_rules({udp_echo, 7001})),
     ok = esockd:allow({udp_echo, 7001}, "10.10.0.0/16"),
     ?assertEqual([{allow, "10.10.0.0/16"},
@@ -447,6 +484,16 @@ t_merge_opts(_) ->
              ],
     ?assertEqual(Result, esockd:merge_opts(Opts1, Opts2)).
 
+t_changed_opts(_) ->
+    Opts1 = [ binary, {acceptors, 8}, {tune_buffer, true}
+            , {ssl_options, [{keyfile, "key.pem"}, {certfile, "cert.pem"}]}
+            ],
+    Opts2 = [ binary, inet6, {acceptors, 16}
+            , {ssl_options, [{keyfile, "key.pem"}, {certfile, "cert.pem"}]}
+            ],
+    Result = [inet6, {acceptors, 16}],
+    ?assertEqual(Result, esockd:changed_opts(Opts2, Opts1)).
+
 t_parse_opt(_) ->
     Opts = [{acceptors, 10}, {tune_buffer, true}, {proxy_protocol, true}, {ssl_options, []}],
     ?assertEqual(Opts, esockd:parse_opt([{badopt1, val1}, {badopt2, val2}|Opts])).
@@ -470,8 +517,9 @@ t_tune_fun_overload(_) ->
     Ret = {error, overloaded},
     LPort = 7003,
     Name = tune_echo_overload,
-    {ok, _LSup} = esockd:open(Name, LPort, [{tune_fun, {?MODULE, sock_tune_fun, [Ret]}}],
-                              {echo_server, start_link, []}),
+    {ok, _LSup} = esockd:open(Name, LPort,
+                              [{tune_fun, {?MODULE, sock_tune_fun, [Ret]}},
+                               {connection_mfargs, {echo_server, start_link, []}}]),
     {ok, Socket} = gen_tcp:connect("127.0.0.1", LPort, [{active, true}]),
     receive
         {tcp_closed, S} ->
@@ -493,8 +541,8 @@ t_tune_fun_ok(_) ->
     LPort = 7004,
     Name = tune_echo_ok,
     {ok, _LSup} = esockd:open(Name, LPort,
-                              [{tune_fun, {?MODULE, sock_tune_fun, [Ret]}}],
-                              {echo_server, start_link, []}),
+                              [{tune_fun, {?MODULE, sock_tune_fun, [Ret]}},
+                               {connection_mfargs, echo_server}]),
     {ok, _S} = gen_tcp:connect("127.0.0.1", LPort, [{active, true}]),
     timer:sleep(10),
     Cnts = esockd_server:get_stats({Name, LPort}),
@@ -524,8 +572,7 @@ do_listener_handle_port_exit(Config, IsTls) ->
                    false -> []
                end,
     %% GIVEN: when listener is started
-    {ok, LSup} = esockd:open(Name, LPort, OpenOpts,
-                              {echo_server, start_link, []}),
+    {ok, LSup} = esockd:open(Name, LPort, [{connection_mfargs, echo_server} | OpenOpts]),
     {LMod, LPid} = esockd_listener_sup:listener(LSup),
     LState = LMod:get_state(LPid),
     PortInUse = proplists:get_value(listen_port, LState),
diff --git a/test/esockd_connection_sup_SUITE.erl b/test/esockd_connection_sup_SUITE.erl
index fd4365f..3d9ce91 100644
--- a/test/esockd_connection_sup_SUITE.erl
+++ b/test/esockd_connection_sup_SUITE.erl
@@ -114,7 +114,7 @@ t_handle_unexpected(_) ->
     {noreply, state} = esockd_connection_sup:handle_info(info, state).
 
 with_conn_sup(Opts, Fun) ->
-    {ok, ConnSup} = esockd_connection_sup:start_link(Opts, {echo_server, start_link, []}),
+    {ok, ConnSup} = esockd_connection_sup:start_link([{connection_mfargs, echo_server} | Opts]),
     Fun(ConnSup),
     ok = esockd_connection_sup:stop(ConnSup).
 
diff --git a/test/esockd_udp_SUITE.erl b/test/esockd_udp_SUITE.erl
index 5b7d97f..d21e885 100644
--- a/test/esockd_udp_SUITE.erl
+++ b/test/esockd_udp_SUITE.erl
@@ -68,8 +68,11 @@ udp_send_and_recv(Sock, Port, Data) ->
     ok.
 
 with_udp_server(TestFun) ->
-    MFA = {?MODULE, udp_echo_init, []},
-    {ok, Srv} = esockd_udp:server(test, {{127,0,0,1}, 6000}, [], MFA),
+    dbg:tracer(),
+    dbg:p(all, c),
+    dbg:tpl({emqx_connection_sup, '_', '_'}, x),
+    MFA = {?MODULE, udp_echo_init},
+    {ok, Srv} = esockd_udp:server(test, {{127,0,0,1}, 6000}, [{connection_mfargs, MFA}]),
     TestFun(Srv, 6000),
     ok = esockd_udp:stop(Srv).