TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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Outgoing traffic using Local(internal) PC IP address to a DDNS hostname

Sorry if the title is confusing. I have two devices connected through the internet. I need device A (Windows Server 2012) to send data down to device B, but unfortunately device B does not have a ...
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1answer
26 views

Is ICMP port unreachable error generated by both TCP and UDP?

I have doubt ! Problem is A program on machine X attempts to open a UDP connection to port 5376 on a machine Y, and a TCP connection to port 8632 on machine Z. However, there are no ...
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24 views

Can someone give me full instructions to open ports required by Starcraft 1 [on hold]

The ports (6112 UDP and TCP) are open in my router, and in the windows firewall yet, I still can't host a game. It does say in netstat that the ports are opened but this webpage says they are not, so ...
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28 views

OpenVPN working with TCP not with UDP

I have successfully set up an OpenVPN server on Debian (raspberry pi model b+). With the protocol set to TCP it works exactly as desired (internet routed through VPN, access to local network ...
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1answer
20 views

Serial over TCP

I have a serial device connected to a remote computer and would like to transmit the serial data from this machine over tcp to another computer, both linux machines. Ideally, I would like to link two ...
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One side TCP ESTABLISHED connection

On the Server 10.10.3.171 I use netstat to find clients : $ netstat -ant | grep 24225 | grep 10.10.3.169 tcp 0 0 10.10.3.171:24225 10.10.3.169:58591 ESTABLISHED tcp 0 ...
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42 views

How come LAST_ACK doesn't enter CLOSE_WAIT?

When a TCP connection is closed at one end of the connection - the other end receives a FIN and responds with an ACK. This end of the connection then enters the CLOSE_WAIT state. Once close() is ...
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On the Performance of TCP implementations of Linux and Windows

I understand the implementation of TCP stack in windows and Linux are different. Windows uses a congestion control algorithm known as the TCP Reno while Linux uses Cubic. How do the 2 protocols ...
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2answers
5k views

Remotely push DNS server to client via OpenVPN

When I try to push a DNS server via the OpenVPN server-config I don't get that server to be the first DNS server on the connected client system. It ends up being specified as an alternative DNS ...
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15 views

How much upstream traffic should a transfer over TCP produce

When a file is downloaded via some TCP-based protocol, there is also data flowing in the other direction – acknowledgement packages etc. Now if I watch some network monitor, I wonder if all of the ...
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50 views

Does Fast Retransmit and Retransmission Timer work at the same time?

When Fast Retransmit is implemented, if I received packet 1, then I will send an ACK that says I need packet 2, and then if I received packet 3, I will send a duplicate ACK that says that I need ...
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25 views

TCP Retransmission on the receiver side

How does Wireshark knows that a packet on the receiver side is being retransmitted. I mean it makes sense on the sender side: Wireshark sees two identical packets (with the same sequence number) being ...
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22 views

How to change the current TCP timestamp value for Linux?

Linux normally sends a TSval field that corresponds to the current uptime. I would like to overwrite this with a user-specified value. # 4 hours after boot: > outgoing TCP packets have TSval ...
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88 views

Why is the FIN flag in TCP called FIN?

There are some flags in TCP. I already understand what other flag names come from, such as SYN stands for synchronization. I also know that FIN is used to close a connection. What I don't understand ...
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1answer
44 views

How much time does TCP waits before retransmission?

If I have a window size of 8 KB, then when 8 KB are sent to the other side and no ACK has been received, TCP will not send anything more until an ACK is received. But what if an ACK is not going to ...
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5answers
15k views

Access Methods to a computer Using MAC Address

I have my own wifi network at home & recently when I checked the active clients on the wifi I found out the there is one active client. Router shows the MAC address of this client and I want to ...
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73 views

haproxy- setting up an TCP connection cache for an HTTP server

I am trying to setup a local TCP connection cache to provide access to a remote HTTP server for multiple local applications. I have started to configure haproxy to do this: global log ...
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1answer
16 views

Not able to login to Tuleap after full installation due to TCP IP port configuration

Not able to login to Tuleap after full installation, as all the ports are in listen mode and 9091 port is not visible in ports.How to over come this and solve. With IP address we are getting tuleap ...
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1answer
28 views

Linux TCP buffer simulation

I would like to run simulations on the Linux TCP receive buffer to find out how big my buffer has to be. Is there any software available to perform such simulation? It would be handy to be able to ...
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1answer
65 views

Why does firefox send TCP packets even when idle?

I run firefox on Debian. I made a clean install with no cookies, or no information input from my side. I've also disabled all mumboo-jumboo healthy and crash report tracking. I've disabled 'shared ...
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3answers
80 views

How to manually send an ARP request

I recently sniffed with Tcpdump a packet "ARP, Request who-has 192.168.2.3 tell 192.168.2.2, length 28". I would like to reproduce this message, and to send an ARP request from my laptop to any IP I ...
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35 views

Tcp connection target machine actively refused

I have a simple TCP client/server program on two laptops. The server should work fine as I use "netstat -anb" and the server shows up as listening, "0.0.0.0:102", then my client connection failed, ...
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1answer
100 views

Which congestion control algorithm is used by the TCP stack in OS X?

What congestion control algorithm is implemented in TCP in OSX 10.9? I would like to know if it uses NewReno, or something newer like Cubic in Linux.
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1answer
46 views

TCP socket to serial port

Is is possibile to remotely access a serial port by tcp socket server? Exists this kind of software? It is the opposit of this question: Any free application to redirect serial communication to ...
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15answers
61k views

How do I kill a process that is dead but listening?

I'm developing an app that listens on port 3000. Apparently there's an instance of it still listening to the port because whenever I start it, it can't create a listener (C#, TcpListener, but that's ...
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Connection interruptions on Debian router, possibly due to excessive duplicate ACKs?

I have a Debian server as a house router, which for a year has been working flawlessly. However, I recently moved and switched service providers from FiOS to Comcast, and possibly as a result am ...
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1answer
50 views

Decrypt SSL at the TCP level

I'm trying to decrypt SSL at the TCP level for data that I'm sending to a remote server. The reason I'm doing this is because the remote host intermittently sends me RSTs, and I'm trying to identify a ...
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1answer
28 views

TCP socket communication from client to server

I am trying to test the performance of a client/server application that uses TCP communication. If I trigger multiple requests from the client, would it flow through the same connection/pipe to the ...
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6 views

Route only on output chain?

I have two machines A and B. I want to send iperf traffic from A to B, but first have it route through a userspace program on A. I did this with a tunneling device: therefore, I used the command ip ...
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47 views

iptables block access to all ports except 53 (tcp,udp) from one IP address

how can i block all ports from one IP address except the port 53 TCP,UDP? example: ip 192.168.0.15 access only port 53 (udp,tcp). thank you.
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69 views

How to tunnel UDP traffic over Tor?

I know that Tor does not support UDP for now . But I came upon certain application Onion Cat .But I don't know if it work or not . Is there any other procedure ? Is that even possible ? Please guide ...
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3answers
2k views

How to monitor TCP connections over time

I have an application which is a windows service. It accesses a number of other services using TCP/IP. E.g. sql server databases, informix databases, mail servers, etc. For instance it will also ...
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2answers
277 views

Data retransmission and WSAECONNABORTED (10053) socket error

Say I have two sockets that are connected to each other (Socket A and Socket B). If the computer that have Socket B is unplugged from power, then if Socket A tries to send some data to Socket B, the ...
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Simultaneous TCP Keep Alive requests no second ack

I have a TCP server running on port 6524 and a client running on port x11 on the same system (Linux sys-111 2.6.32-431.29.2.el6.x86_64). Both these send TCP Keep alive messages to keep the connection ...
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1answer
106 views

ISP Issues - TCP Out-of-Order

Accessing any webpage (basically any TCP connection), results in multiple retries before and long loading times before it loads a page with missing elements (reload might fix it). Google Chrome throws ...
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2answers
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Are FIN packets guaranteed to arrive?

In the 4-way handshake, we have the following: FIN -------> <------- ACK <---x--- FIN (what if this packet is lost?) ACK -------> What happens if the third packet is lost, will it be ...
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3answers
14k views

what is TCP Half Open Connection and TCP half closed connection

I am trying to understand what is the difference between TCP Half Open Connection and TCP Half closed connection can any one tell what exactly are they?
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Monitor TCP port traffic and get a sound alert when a specific text string is found on Windows

I need to watch a port for several hours and make an audible alert whenever a specific string comes through. Windows only. Is this possible with Wireshark or another sniffer tool or maybe a sniffer ...
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1answer
91 views

Bittorrent client makes multiple connections upon its start to amazonaws

I have this weird situation that every time I open my bittorrent client application, upon its start, it starts to make a lot of multiple connections(more than thousands) to amazonaws servers and as ...
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1answer
71 views

How to share via TCP serial port CAT

I want to connect my amateur radio transceiver to a linux (Ubuntu) computer with USB cable (serial port (in windows should be COM3 or COM4) like /dev/??? ) and share it locally with TCP, Is it ...
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124 views

Should I disable Netbios over TCP/IP for printing throught Samba+cups?

I have a domain with 100+ machine which are reparted on two IP ranges. On this moment, computers are using netBIOS over TCP/IP or SMB over TCP/IP. It seem that two requests are send ...
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1answer
3k views

What happens to TCP connections when I remove the ethernet cable?

For a TCP connection, when I remove the cable and reconnect after 30-40 seconds there is no packet loss issues. But when the reconnect time is more than a few minutes all the packets are lost. I know ...
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5answers
783 views

What ports are used by an application [duplicate]

I'm testing an application which opens its own ports (acts as a server for these ports, hence listens at that ports) and where the same application connects to ports bound by other applications (acts ...
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1answer
67 views

Man in the middle using iptables

I wish to test a subsystems which communicates with another subsystems via tcp. I have used the following: "iptables -A OUTPUT -p tcp --dport "+port_number" -j DROP" to stop the traffic on a port ...
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2answers
194 views

If HTTP runs on a port, does that mean TCP can also run on that port?

I'm building an app that needs to run on a mobile smartphone over a GPRS/3G network. I'm doing bit ops, so every byte wasted through HTTP headers is bad. Mobile providers in my area make heavy use of ...
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51 views

What is the primary function of the transport layer in the Internet protocol networking code [closed]

I am not sure if I have answered this question right, so would appreciate it if someone could correct me. The question is: What is the primary function of the transport layer in the Internet protocol ...
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1answer
109 views

VMware TCP port mapping not working - port not accessible via public IP address

Simply speaking, the forwarded port 45922 is accessible on the host via 127.0.0.1:45922, but not accessible on the host itself via its public IP plus port number 45922. Details are as follows. Host ...
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61 views

List all open sockets in /dev/tcp/localhost/

Is it possible to list all open sockets in /dev/tcp/localhost/ on a Linux machine? I want to list all sockets where the following command would return 0: timeout 2 bash -c "cat < /dev/null > ...
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211 views

TCP congestion control Windows 7

Based on what I read, Compound TCP is disabled by default in Windows 7. If so, which default congestion control algorithm does windows 7 use? Is it TCP RENO or NEW RENO? Could you give me some links ...