TCP/IP matters

Hi to all
I was just wondering if it is necessary to close TCP/IP connection after an error(e.g connection lost) had occured. Is it ok if I just reopen another connection to the same IP and port without closing the existing connection(that connection which the error had occurred)? Will this lead to any conflicts in my program?
Another matter is, is it possible to query the IP of an device connected to my computer?
Thank you.
Solved!
Go to Solution.

rdtttttttttttttt wrote:
Thanks for all your answers.
I meant finding unknown Ip address of some device connected to comp.
There is no standard way a TCP/IP device (server) would announce its availability on a network. So each device/server employs its own method. This could be an UDP broadcast inquery to which it will listen on a well known port and send back an UDP packet to the requester with information such as its IP address.
Or there is a well known service in the network which can receive service registrations and cancelations and stores all registered services internally. Then a client can inquiry at that registrar service for a specific service name and receives the according information to be able to connect to it.
There are probably 500 other ways to skin this cat and all have for sure been tried by some device manufacturers.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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rwengr wrote:
My problem is that tomcat/servlet is not releasing its TCP port after my servlet closes the port. Next time a servlet tries to use the port it gets an error "Port already in use". Using netstat I can see the port is still in use. If I stop tomcat and restart it, the port is released. I have not had this sort of problem writing C programs that use sockets.Nice.... Not sure that matters though.
>
My setup is Fedora Core 6 with JDK1.5_14 and Tomcat 5.5.26. I know it's not the latest, but sockets and streams have been around for a long time.
Actual implementation uses a trivial javaserver page to instantiate a class to create/accept connection from a client (JApplet). Bleah! Don't use a JSP for that. Use a servlet at worst. At best use a Servlet to start some other socket manager class which you can/have tested outside the Servlet Container environment.
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Error Details LOCATION: SAP-Gateway on host <hostname> / sapgw<instance no>
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Error Details    COUNTER: 77326
Error Details    MODULE: gwr3cpic.c
Error Details    LINE: 1778
Error Details    RETURN CODE: 679
Error Details    SUBRC: 0
Error Details    RELEASE: 700
Error Details    TIME:
Error Details    VERSION: 2
Procedure Tried
1) This procedure is for Linux OS - Similarly we tried in Windows OS ( If any procedure is wrong also, Please correct us)
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2)
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Edited by: saptest2011 on May 20, 2011 5:36 PM

Hello SM,
Thanks for your quick reply.
Thanks for sharing link for document ie Configure the MDM Administration_cockpit. It is helpful. I read that document.
But still issue remain there.
The same RFC connection works between SRM sandbox to MDM sandbox.
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difference between MDM Prod and MDM sandbox.
MDM Prod runs: Windows server 2008 OS
MDM Sandbox runs: Windows server 2003 OS
Landscape: PI7.1, MDM 7.1 and SRM 5.5, SRM-MDM Catalog 3.0
Even i did os01 tcode ping test using host name (specific IP address) from SRM prod to MDM prod, it is fine.
Thanks a lot for your help.
I checked these notes also
Note 353597 - Registering a server program
Note 44844 - No connection to registered RFC program
Note: in smgw tcode in SRM system, the required program id is not showing in logged on clients
Thanks
Edited by: saptest2011 on May 23, 2011 5:00 PM
Edited by: saptest2011 on May 23, 2011 5:39 PM

XModem via TCP for Java

I am sure that many of you experienced developers have read requests in the past concerning implmentation of Ward Christenen's XModem protocol over a TCP socket. If not, well... you are about to...
This is a major hack... but it is starting to come together... thanks to Fred Potter for his source code to start this project...
Objective:
Basically, I want to create a console application which accepts an incoming connection and starts the receive mode for a XModem file transfer. I am using CGTerm (for Commodore retrocomputing) but can test with HyperTerminal as well...
The user who connects to the server selects SEND and the FILE to send for a XModem file transfer... and the transfer begins...
The incoming blocks of 128 bytes are written to a file
After the transfer is over the server disconnects the client terminal.
Here is what I have so far:
import java.net.*;
import java.lang.*;
import java.io.*;
// X-Modem Server implementation via TCP/IP socket
public class XServer {
public static FileWriter fw;
public static void main(String[] args) throws IOException {
// define the file
try {
fw = new FileWriter("filename.txt");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
int port = Integer.parseInt(args[0]);
ServerSocket server = new ServerSocket(port);
System.out.println("X-Server v1.0 - waiting for connection");
Socket client = server.accept();
// Handle a connection and exit.
try {
InputStream inputStream = client.getInputStream();
OutputStream outputStream = client.getOutputStream();
new PrintStream(outputStream).println("Go to send file mode!"); // sent to client
System.out.println("Ready to receive file via X-Modem...");
* BEGIN TRANSFER HERE!
// set the debug flag
XModem.debug = true;
* Here we are instantiating a new InputStream that represents the remote
* file that we are receiving. In this single line we are attempting to
* start the flow.
* Behind The Scenes: We're sending a NAK across the serial line repeatedly
* until we finaly start seeing the data flow. If we don't see the data
* flow, then we throw an exception.
System.out.println("Sending NAK to start receive mode...");
InputStream incomingFile;
try {
incomingFile = new XModemRXStream(inputStream, outputStream);
} catch (IOException e) {
System.out.println("ERROR! Unable to start file transfer!");
e.printStackTrace();
return;
System.out.println("Starting file transfer...");
* Here we are reading from the incoming file, byte by byte, and printing out.
* Behind The Scenes: Internally, the read() method is handling the task of
* asking for the next data block from the remote computer, processing it (i.e.
* parsing, running checksums), and then putting it in an internal buffer. Not
* all calls to read() will request a new data block as each block contains at
* least 128 bytes of data. Sometimes you will only hit the buffer.
try {
for (;;) {
int c = incomingFile.read();
if (c==-1)
break; // End of File
// print character / byte
System.out.print(c+",");
// write to file
try {
//System.out.print(".");
fw.write(c);
} catch (Exception e) {
System.out.println(e);
System.exit(0);
} catch (IOException e) {
System.out.println("error while reading the incoming file.");
e.printStackTrace();
return;
// done
System.out.println("File sent.");
new PrintStream(outputStream).println("");
new PrintStream(outputStream).println("transfer successful!");
} finally {
//client.close();
// save the file
try {
fw.close();
System.out.println("file saved.");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
* XModem keeps track of settings that the Receive and Transmit Stream classes will
* reference.
* <p>Copyright: Copyright (c) 2004</p>
* @author Fred Potter
* @version 0.1
class XModem {
public static boolean debug = false;
* XModemRXStream is an easy to use class for receiving files via the XModem protocol.
* @author Fred Potter
* @version 0.1
class XModemRXStream
extends InputStream {
// CONSTANTS
private static final int SOH = 0x01;
private static final int EOT = 0x04;
private static final int ACK = 0x06;
private static final int NAK = 0x15;
private static final int CAN = 0x18;
private static final int CR = 0x0d;
private static final int LF = 0x0a;
private static final int EOF = 0x1a;
// block size - DON'T CHANGE - I toyed with the idea of adding 1K support but the code is NOT there yet.
private static final int bs = 128;
// PRIVATE STUFF
private int ebn; // expected incoming block #
private byte[] data; // our data buffer
private int dataPos; // our position with the data buffer
private InputStream in;
private OutputStream out;
* Creates a new InputStream allowing you to read the incoming file. All of the XModem
* protocol functions are handled transparently.
* As soon as this class is instantiated, it will attempt to iniatate the transfer
* with the remote computer - if unsuccessful, an IOException will be thrown. If it
* is successful, reading may commense.
* NOTE: It is important not to wait too long in between calls to read() - the remote
* computer will resend a data block if too much time has passed or even just give up
* on the transfer altogether.
* @param in InputStream from Serial Line
* @param out OutputStream from Serial Line
public XModemRXStream(InputStream in, OutputStream out) throws
IOException {
this.in = in;
this.out = out;
// Initiate the receive sequence - basically, we send a NAK until the data
// starts flowing.
init:for (int t = 0; t < 10; t++) {
if (XModem.debug) {
System.out.println("Waiting for response [ try #" + t + " ]");
long mark = System.currentTimeMillis();
out.write(NAK);
// Frequently check to see if the data is flowing, give up after a couple seconds.
for (; ; ) {
if (in.available() > 0) {
break init;
try {
Thread.sleep(10);
catch (Exception e) {}
if (System.currentTimeMillis() - mark > 2000) {
break;
// We have either successfully negotiated the transfer, OR, it was
// a failure and timed out. Check in.available() to see if we have incoming
// bytes and that will be our sign.
if (in.available() == 0) {
throw new IOException();
// Initialize some stuff
ebn = 1; // the first block we see should be #1
data = new byte[bs];
dataPos = bs;
* Reads the next block of data from the remote computer. Most of the real XModem protocol
* is encapsulated within this method.
* @throws IOException
private synchronized void getNextBlock() throws IOException {
if (XModem.debug) {
//System.out.println("Getting block #" + ebn);
// Read block into buffer. There is a 1 sec timeout for each character,
// otherwise we NAK and start over.
byte[] buffer;
recv:for (; ; ) {
buffer = new byte[bs + 4];
for (int t = 0; t < 10; t++) {
System.out.println("\nReceiving block [ #" + ebn + " ]");
// Read in block
buffer = new byte[buffer.length];
for (int i = 0; i < buffer.length; i++) {
int b = readTimed(1);
// if EOT - don't worry about the rest of the block.
if ( (i == 0) && (b == EOT)) {
buffer[0] = (byte) (b & 0xff);
break;
// if CAN - the other side has cancelled the transfer
if (b == CAN) {
throw new IOException("cancelled");
if (b < 0) {
if (XModem.debug) {
System.out.println("Time out... NAK'ing");
out.write(NAK);
continue recv;
else {
buffer[i] = (byte) (b & 0xFF);
break;
int type = buffer[0] & 0xff; // either SOH or EOT
if (type == EOT) {
if (XModem.debug) {
System.out.println("EOT!");
out.write(ACK);
break;
int bn = buffer[1] & 0xff; // block number
int bnc = buffer[2] & 0xff; // one's complement to block #
if (
(bn != ebn) && (bn != (ebn - 1)) ||
(bn + bnc != 255)) {
if (XModem.debug) {
System.out.println("NAK'ing type = " + type + " bn = " + bn +
" ebn = " +
ebn + " bnc = " + bnc);
out.write(NAK);
continue recv;
byte chksum = buffer[ (buffer.length - 1)];
byte echksum = 0;
for (int i = 3; i < (buffer.length - 1); i++) {
echksum = (byte) ( ( (echksum & 0xff) + (buffer[i] & 0xff)) & 0xff);
if (chksum != echksum) {
out.write(NAK);
continue recv;
out.write(ACK);
if (ebn == 255) {
ebn = 0;
else {
ebn++;
break;
// We got our block, now save it in our data buffer.
data = new byte[bs];
for (int i = 3; i < (buffer.length - 1); i++) {
data[(i - 3)] = buffer;
dataPos = 0;
public synchronized int read() throws IOException {
// If at the end of our buffer, refill it.
if (dataPos == bs) {
try {
getNextBlock();
catch (IOException e) {
throw new IOException();
// If we're still at end of buffer, say so.
if ( dataPos == bs) {
return -1;
int d = data[dataPos];
if (d == EOF)
return -1;
dataPos++;
return d;
* A wrapper around the native read() call that provides the ability
* to timeout if no data is available within the specified timeout value.
* @param timeout timeout value in seconds
* @throws IOException
* @return int an integer representing the byte value read.
private int readTimed(int timeout) throws IOException {
long start = System.currentTimeMillis();
for (; ; ) {
if (in.available() > 0) {
return (in.read());
try {
Thread.sleep(10);
catch (InterruptedException ex) {
//if (System.currentTimeMillis() - start > timeout * 1000) {
if (System.currentTimeMillis() - start > timeout * 5000) {
return -1;
Here was the output...
Original file:
(Commodore CBM SEQ file exported to PC using DirMaster)
��
� �
� ��
� ��
� ��
��
� ��
� � ��
��
� � ��OWERED BY �OLOR 64 �� V8
�UNNING �ETWORK64 V1.26A
�
�UPPORTING 38400 �AUD �ATES
��/��/��
�
�ESTING �CHO-�ET V1 BETA
�
�EATURING �ESSAGES, �ILES,
�ET�AIL, AND �NLINE �AMES!
�YS�P: � � � � � � � � �
�
�RESS ANY KEY TO LOGIN\C�
The result when the file was uploaded and received by my XServer:
? ? ??OWERED BY ?OLOR 64 ??? V8
?UNNING ?ETWORK64 V1.26A
?UPPORTING 38400 ?AUD ?ATES
?ESTING ?CHO-?ET V1 BETA
?EATURING ?ESSAGES, ?ILES,
?ET?AIL, AND ?NLINE ?AMES!
?YS?P: ? ? ? ? ? ? ? ? ?
?RESS ANY KEY TO LOGIN\C?
The result is different!
Can someone help me along here... I have been trying to figure out how to do this for approx. a year or so... it has been a very slow process.
I could use a guru to help me out so I can write the upload and download routines for my Commodore BBS PETSCII Emulation Server.
Visit http://www.retrogradebbs.com for details.
Thanks.
Please help out a dedicated developer who is in over his head...
-Dave

Ok. Fair enough. What about general information about Xmodem. This is a hard project because of how obscure the legacy technology is that I am having to implement using Java and MySQL.
I have two major issues which I have to figure out how to troubleshoot and debug, if possible.
1. The 23+ blocks exception when a file is being received
2. The exception which is thrown immediately if I try to receive a binary file instead of an ASCII file.
I read that telnet is a 7-bit technology and that is why Xmodem, which is an 8-bit technology is not that popular as a viable protocol via telnet, whereas Kermit is, since it was developed for 7-bit systems, i.e. mainframes and minicomputers.
Is this correct?
If that is the case, why does www.serio.com have a viable X-Y-ZModem library available (for several hundred $$$ of course) which can be used with both RS-232 serial ports and TCP socket ports? Obviously, it can be done. They are the ONLY company with this library for sale for Java to do this. I cannot justify that $$$ amount for a mere hobby (writing the BBS emulation server for supporting Commodore PETSCII (CG) callers via CGTerm or a native C-64 terminal program using Jim Brain's TCPSER middleware, which emulates a Hayes modem via telnet for telBBSing/retrocomputing.
I really want to learn how to implement a file transfer protocol, since back in the 80s, I used Xmodem, Punter, Y/Z Modem, etc., a lot to upload and download files via modem at baud rates of 2400, 14.4, 19.2, and 38.4, respectively.
It's fun to learn how the old skool gurus of telecommunications technology did it. It is one thing to run a BBS which supports these technologies and features, and it is an entirely other thing to learn how to design and develop them yourself for implementation into a project such as I taken on.
It CAN be done. It WILL be done. However, I have just started my exhaustive research on how it needs to be done. I have read up as much as I could on XModem by Ward C., the father of the protocol.
But, I have no information to help me figure out why the communications are acting as they do so far.
Can someone please download the xserver.zip file on my website at:
www.retrogradebbs.com/projects/xserver.zip
Compile it. Run it. Connect using HyperTerminal, Netrunner, or another telnet terminal emulation program which supports Xmodem file transfers using WinSock.
See what happens. With finals due in the next two days, this project will have to be put on hold until after I submit my two final projects.
If anyone knows what needs to be done to support both ASCII and BINARY file transfers via Xmodem via a socket instead of a modem with RTS/CTS hardware flow control, please respond.
I know for a fact that this can be done.
- Dave

Getting the data from a TCP/IP packet

I am dealing with an industrial network that sends and recieves data over TCP/IP between a sort of supervisory system running on Unix and some machines via a bridge that converts messages onto other non TCP/IP networks. This is all old legacy equipment and the bridge now need upgrading. However the original source code is not availiable and no-one is very sure of the messages being sent. I thought it was going to be easy knocking something together in Java to intercept these messages and test various things but have come up against big problems.
The main problem being that all the data is binary meaning I cant use any of the reader or writer classes I am used too. I am trying to use either DataInputStream or BufferedInputStream to read data in but am struggling. Idealy I need to be able to read (once) the complete data content of each packet that is sent and I need to tell each time a new packet of data arrives so that I can process it as a complete packet. As far as I know there are no eof or eol or any other details that tell me how many bytes of data there are, and they do vary in length, but each packet is a seperate message or message reply.
I was hoping that there might be someway of getting this information from the TCP/IP layers but cant see how to do it as that all seems to work invisibly. Nor can I see any methods to call on the stream classes that indicate how to tell the lenght of the latest packet or when a new packet has arrived. I am not sure how some of the methods like mark() and reset|() are supposed to be used so am not sure if I couuld use these but am desperate for any help or pointers in the right direction.

The TCP/IP packets can represent complete messagesThere is no guarantee to this effect anywhere in TCP/IP. Consider the case where a single message requires multiple writes. Consider the case where a write contains the end of one message and the beginning of another. Consider the case where there are multiple messages in a single packet. Consider ... There are just too many of these cases.
The TCP/IP takes care of numbering the packets so that they can be reasembled in the correct order. Each TCP/IP packet contains information about the size of data the packet contains ...Thank you, I do know how TCP works.
so in theory if we could get at the TCP/IP layers we should be able to get this information.No. You can get all the packet information out of packets. What you can't get is message information, because it isn't in there. It's in the application protocol, which to TCP/IP is just a stream of bytes. You can get the stream of bytes that the application sent. What it means is up to you.
I really need to be able to read each packet of data seperately to be able to do anything with itWhy? Given the lack of correlation between writes() and packets and reads() due to TCP streaming, what is the point? And if you want packets you already have them via your sniffer.
From your first post:
each packet is a seperate message or message reply.You can't rely on that. There is no guarantee of this anywhere in TCP/IP.
I also direct your attention to the Nagle algorithm, which coalesces outgoing packets under common conditions.

TCP/IP does not let me enable or disable.

Hi,
I am trying to enable TCP/IP in order to access my SQL server remotely but when I select tcp/ip and want to enable = Yes or disabled = no it does not give me the option, it appears a gray empty rectangle.
Any idea what might happen?, I will like to post a picture but it does not let me at the moment
Thank you,

This one may help.
Enable Named Pipes and TCP/IP Connections
Might also ask them over here.
SQL Server forums on MSDN
Regards, Dave Patrick ....
Microsoft Certified Professional
Microsoft MVP [Windows]
Disclaimer: This posting is provided "AS IS" with no warranties or guarantees , and confers no rights.

Lync 2013 mobile app does not work internally, SIP domain is Different than users UPN. not sure if that matters.

using the lync client connectivity tester on a pc on the same lan as my mobile client everything is green and it says its ready for use.
using my android galaxy s5 client on wifi on the same lan i get a screen with waiting to sign in spinning and an error at the top "we cant connect to the server check your network connection and server address, and try again."
i have uploaded the full client log files
here: client log file
some errors that stand out from this log file are:
1. ERROR HttpEngine: Certificate check fails: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.
2. <h2>401 - Unauthorized: Access is denied due to invalid credentials.</h2>
<h3>You do not have permission to view this directory or page using the credentials that you supplied.</h3>
i am using the correct creds, same creds i used on the analyzer tool.
in the analyzer tool i did have to fill in the username field because my sip domain is different then my users UPN. which from what ive read its required to use the username field.
i also filled in the username field in the mobile app with domain\username
3. ERROR LYNC: ERROR TRANSPORT /Volumes/ServerHD2/buildagent/workspace/200604/tps/ucmp/platform/networkapis/privateandroid/CHttpConnection.cpp/295:CHttpConnection exception: java.lang.NullPointerException
Jan 14, 2015 8:40:49 AM INFO LYNC: INFO TRANSPORT /Volumes/ServerHD2/buildagent/workspace/200604/tps/ucmp/ucmp/transport/requestprocessor/private/CHttpRequestProcessor.cpp/173:Received response of request(UcwaAutoDiscoveryRequest) with status = 0x22020001
Jan 14, 2015 8:40:49 AM INFO LYNC: INFO TRANSPORT /Volumes/ServerHD2/buildagent/workspace/200604/tps/ucmp/ucmp/transport/requestprocessor/private/CHttpRequestProcessor.cpp/201:Request UcwaAutoDiscoveryRequest resulted in E_ConnectionError (E2-2-1). The retry
counter is: 0
4. Jan 14, 2015 8:40:50 AM ERROR LYNC: ERROR TRANSPORT /Volumes/ServerHD2/buildagent/workspace/200604/tps/ucmp/ucmp/transport/authenticationresolver/private/CAuthenticationResolver.cpp/431:Failing the original request as we weren't able to get the token
this is the same type of error i was getting in the lync connectivity analyzer until i filled in the username field. but its filled in, in my client.
again you can see the full log file is `HERE
thank you in advance for any help. im trying to get internal working before i try external.

Eric,
I am trying to configure a reverseproxy on my netscaler which is in a 2 arm mode(dmz/internal) but I keep getting an error when configuring the monitor.
i used this guide to configure it
http://www.lynced.com.au/2014/04/configure-citrix-netscaler-vpx-as.html
but continue to get this error in the netscaler monitor "Failure - TCP connection successful, but application timed out"
so the virtual server is never up, thinking about just changing it to tcp as a monitor so it stays up and i can at lesat get the vip up.
Also your link to the diagram shows it going to the reverse proxy but the one im using has it going directly to the front end servers.
http://www.lync-solutions.com/Documents/Lync_2013_protocol_poster_v6_7.pdf
I'm guessing Microsoft's is the correct one but wonder why the config differential?
I see that your diagram says "mobility url", what is the mobility url? i though that was the lyncdiscoverinternal.internal.com
current setup is
2 fe servers on internal
1 edge server on dmz
1 almost done reverse proxy netscaler load balancer.
also this ms link i used to configure dns entries, along with the pdf linked above.
http://technet.microsoft.com/en-us/library/jj945644.aspx
i currently have these external dns entries and they all point to the edge server on the dmz.
dialin .external.com
lync .external.com
lyncweb .external.com
lyncdiscover.external.com
meet .external.com
sip .external.com
webconf .external.com
av .external.com
_autodiscover._tcp.external.com.
the internal dns links point to 1 of the front end servers
1. lyncdiscoverinternal.internal.com
2. lyncdiscover.internal.com
3. _sipinternaltls._tcp.internal.com
4. _sipinternal._tcp.internal.com
5. sipinternal.internal.com
6. sip.internal.com
thanks again for your help.

Async tcp client and server. How can I determine that the client or the server is no longer available?

Hello. I would like to write async tcp client and server. I wrote this code but a have a problem, when I call the disconnect method on client or stop method on server. I can't identify that the client or the server is no longer connected.
I thought I will get an exception if the client or the server is not available but this is not happening.
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
How can I determine that the client or the server is no longer available?
Server
public class Server
private readonly Dictionary<IPEndPoint, TcpClient> clients = new Dictionary<IPEndPoint, TcpClient>();
private readonly List<CancellationTokenSource> cancellationTokens = new List<CancellationTokenSource>();
private TcpListener tcpListener;
private bool isStarted;
public event Action<string> NewMessage;
public async Task Start(int port)
this.tcpListener = TcpListener.Create(port);
this.tcpListener.Start();
this.isStarted = true;
while (this.isStarted)
var tcpClient = await this.tcpListener.AcceptTcpClientAsync();
var cts = new CancellationTokenSource();
this.cancellationTokens.Add(cts);
await Task.Factory.StartNew(() => this.Process(cts.Token, tcpClient), cts.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
public void Stop()
this.isStarted = false;
foreach (var cancellationTokenSource in this.cancellationTokens)
cancellationTokenSource.Cancel();
foreach (var tcpClient in this.clients.Values)
tcpClient.GetStream().Close();
tcpClient.Close();
this.clients.Clear();
public async Task SendMessage(string message, IPEndPoint endPoint)
try
var tcpClient = this.clients[endPoint];
await this.Send(tcpClient.GetStream(), Encoding.ASCII.GetBytes(message));
catch (Exception exception)
private async Task Process(CancellationToken cancellationToken, TcpClient tcpClient)
try
var stream = tcpClient.GetStream();
this.clients.Add((IPEndPoint)tcpClient.Client.RemoteEndPoint, tcpClient);
while (!cancellationToken.IsCancellationRequested)
var data = await this.Receive(stream);
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
private async Task Send(NetworkStream stream, byte[] buf)
await stream.WriteAsync(BitConverter.GetBytes(buf.Length), 0, 4);
await stream.WriteAsync(buf, 0, buf.Length);
private async Task<byte[]> Receive(NetworkStream stream)
var lengthBytes = new byte[4];
await stream.ReadAsync(lengthBytes, 0, 4);
var length = BitConverter.ToInt32(lengthBytes, 0);
var buf = new byte[length];
await stream.ReadAsync(buf, 0, buf.Length);
return buf;
Client
public class Client
private TcpClient tcpClient;
private NetworkStream stream;
public event Action<string> NewMessage;
public async void Connect(string host, int port)
try
this.tcpClient = new TcpClient();
await this.tcpClient.ConnectAsync(host, port);
this.stream = this.tcpClient.GetStream();
this.Process();
catch (Exception exception)
public void Disconnect()
try
this.stream.Close();
this.tcpClient.Close();
catch (Exception exception)
public async void SendMessage(string message)
try
await this.Send(Encoding.ASCII.GetBytes(message));
catch (Exception exception)
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
private async Task Send(byte[] buf)
await this.stream.WriteAsync(BitConverter.GetBytes(buf.Length), 0, 4);
await this.stream.WriteAsync(buf, 0, buf.Length);
private async Task<byte[]> Receive()
var lengthBytes = new byte[4];
await this.stream.ReadAsync(lengthBytes, 0, 4);
var length = BitConverter.ToInt32(lengthBytes, 0);
var buf = new byte[length];
await this.stream.ReadAsync(buf, 0, buf.Length);
return buf;

Hi,
Have you debug these two applications? Does it go into the catch exception block when you close the client or the server?
According to my test, it will throw an exception when the client or the server is closed, just log the exception message in the catch block and then you'll get it:
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.Invoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
Console.WriteLine(exception.Message);
Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
By the way, I don't know what the SafeInvoke method is, it may be an extension method, right? I used Invoke instead to test it.
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Jabber 9.2 Failback from TCP 5222 to TCP 443

Hi all,
if i check the deployment guide for J4W i see that it supports failback to https, if XMPP (TCP 5222) is not available.
http://www.cisco.com/en/US/docs/voice_ip_comm/jabber/Windows/9_2/JABW_BK_C9731738_00_jabber-windows-install-config_chapter_010.html#JABW_RF_P3E0FDE4_00
We have noticed that the feature is not available in our cloud based deployment.
Do i have to enable eny specific setting in Webex Connect Admin?
Any other experiences?
Steffen

One of us does not understand the feature.
Of course is 5222 blocked, because I want to see jabber doing a fail back to https.
Do I misunderstand the fail back?
Sent from Cisco Technical Support iPad App

ASA 5505:Static Routing and Deny TCP connection because of bad flag

Hi Everybody,
I have a problem. I made a VPN site-2-site with 2 ASA 5505. The VPN works great. And I create a redondant link if the VPN failed.
In fact, I use Dual ISP with route tracking. If the VPN fails, the default route change to an ISDN router, situated on the inside interface.
When I simulated a VPN fail, the ASAs routes switch automatically on backup ISDN routers. If I ping elements, it works great. But when i try TCP connection like telnet, the ASAs deny connections:
%PIX|ASA-6-106015: Deny TCP (no connection) from 172.16.10.57/35066 to 172.16.18.1/23 flags tcp_flags on interface interface_name.
the security appliance discarded a TCP packet that has no associated connection in the security appliance connection table. The security appliance looks for a SYN flag in the packet, which indicates a request to establish a new connection. If the SYN flag is not set, and there is not an existing connection, the security appliance discards the packet.
thanks!
EDIT: On the schema, The interface of the main asa is 172.16.18.148...

Check if the xlate timer is set greater than or equal to what the conn timer, so as not to have connections waiting on xlates that no longer exist. To minimize the number of attempts, enable "service resetinbound" . The PIX will reset the connection and make it go away. Without service resetinbound, the PIX Firewall drops packets that are denied and generates a syslog message stating that the SYN was a denied connection.

TCP/IP matters

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