Docker-plugin on Jenkins fails to Test Connection

I have ubuntu server with installed docker on it.
I have deployed Jenkins on Docker with installed docker-plugin on it.

I am trying to add Cloud-docker, with params:

jenkins.version is 1.597

name: docker
Docker Url: 172.17.42.1:4243
connection timeout: 5
read timeout: 15

But I am getting all the time Connection refused error during Test Connection:

javax.servlet.ServletException: javax.ws.rs.ProcessingException:
java.net.ConnectException: Connection refused at
org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796) at
org.kohsuke.stapler.Stapler.invoke(Stapler.java:876) at
org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249) at
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746) at
org.kohsuke.stapler.Stapler.invoke(Stapler.java:876) at
org.kohsuke.stapler.Stapler.invoke(Stapler.java:649) at
org.kohsuke.stapler.Stapler.service(Stapler.java:238) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:848) at
org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686)
at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1494)
at
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:123)
at
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:114)
at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48) at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164) at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at
org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at
hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at
org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
at
org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
at
org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
at
org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
at
org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
at
org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
at
org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
at
org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
at
org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
at
org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
at
org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java:370) at
org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
at
org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960)
at
org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)
at
org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
at
org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
at
org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
at
org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
at
winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745) Caused by:
javax.ws.rs.ProcessingException: java.net.ConnectException: Connection
refused at
org.glassfish.jersey.client.HttpUrlConnector.apply(HttpUrlConnector.java:184)
at
org.glassfish.jersey.client.ClientRuntime.invoke(ClientRuntime.java:227)
at
org.glassfish.jersey.client.JerseyInvocation$3.call(JerseyInvocation.java:693)
at org.glassfish.jersey.internal.Errors.process(Errors.java:315) at
org.glassfish.jersey.internal.Errors.process(Errors.java:297) at
org.glassfish.jersey.internal.Errors.process(Errors.java:228) at
org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:422)
at
org.glassfish.jersey.client.JerseyInvocation.invoke(JerseyInvocation.java:689)
at
org.glassfish.jersey.client.JerseyInvocation$Builder.method(JerseyInvocation.java:405)
at
org.glassfish.jersey.client.proxy.WebResourceFactory.invoke(WebResourceFactory.java:318)
at com.sun.proxy.$Proxy51.version(Unknown Source) at
com.nirima.docker.client.DockerClient$System.version(DockerClient.java:116)
at
com.nirima.jenkins.plugins.docker.DockerCloud$DescriptorImpl.doTestConnection(DockerCloud.java:341)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606) at
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161) at
org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:121) at
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746) … 48
more Caused by: java.net.ConnectException: Connection refused at
java.net.PlainSocketImpl.socketConnect(Native Method) at
java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at
java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at
java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) at
java.net.Socket.connect(Socket.java:579) at
sun.net.NetworkClient.doConnect(NetworkClient.java:175) at
sun.net.www.http.HttpClient.openServer(HttpClient.java:432) at
sun.net.www.http.HttpClient.openServer(HttpClient.java:527) at
sun.net.www.http.HttpClient.(HttpClient.java:211) at
sun.net.www.http.HttpClient.New(HttpClient.java:308) at
sun.net.www.http.HttpClient.New(HttpClient.java:326) at
sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:996)
at
sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:932)
at
sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:850)
at
sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1300)
at
java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:468)
at
org.glassfish.jersey.client.HttpUrlConnector._apply(HttpUrlConnector.java:276)
at
org.glassfish.jersey.client.HttpUrlConnector.apply(HttpUrlConnector.java:182)
… 70 more

what could be wrong?

thanks