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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Program running from a folder where a parent folder is not accessible wont be able to use tcp layer

This issue is one that has taken me and our IT department at our company many hours to pinpoint. The problem only appears on Windows server 2008, windows 7 and windows 8. On Windows XP or Windows ...
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1answer
255 views

Using tcpdump on displayed TCP data

If sudo tcpdump -i eth0 -X gives me tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes ...
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370 views

Ubuntu openVPN TCP no internet, UDP works. Win7 works on both TCP/UDP with same settings

I've recently purchased a VPN service which I'm connecting to with openVPN. On Windows 7 I can connect on both UDP and TCP settings, but when I'm trying the same thing on Ubuntu 13.04, it gives me ...
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I think that someone else is entering my computer for long, sth like back orifice. I then got TCPView. Now, what do I do?

I got some variations of the name of my own computer going on in TCPView, for instance. I wonder whether that means another computer, like in one instance the name appears in capital letters, in ...
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225 views

Can't telnet: TCP connection doesn't get established

I am having issues with telnet from a machine. TCP connection is not getting established. SYN gets sent out and SYN_ACK comes back but not sure why the ACK is not getting sent back. I am guessing ...
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588 views

Connection stays alive but endpoint is dead?

Does anyone have an idea what would cause a TCP connection (client side) to stay in the ESTABLISHED state for about 24 hours, even though the server was restarted? The client process stays on the ...
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How do IP answer packets reach their destination inside of a private LAN?

This is a little theory question that has been confusing me for a pretty long time. Basically, if we are inside of a private LAN, and we want incoming packets to reach, for example, an HTTP server ...
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136 views

Using and testing UDP data over the internet [duplicate]

I have a GSM modem that sends data via UDP (it appears) I have configured it to send all data to my public IP address over the internet but no data is arriving at my end so I need to troubleshoot. I ...
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349 views

Server response in TCP 3-way handshake

A server normally responds with SYN ACK in a 3-way handshake. What would happen if it just responded with ACK?
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400 views

Any free program for binary TCP communication?

I have a TCP server listening on a localhost's port so I need a software that can be used to establish a TCP connection to the server and then send binary data, not ASCII. For example, I want to send ...
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2answers
106 views

Does TCP care about the incoming port?

Does TCP care if the port changes on a SYN/ACK that comes back compared to the destination port asked for? I.E. If i have a port forward turning 80 into 8080, and the client sends a SYN on 80 and ...
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60 views

TCP freeze problems

I have a server which I am testing for functionality (not load, not stress) with tsung. 50 users / second, 100 total users. Judging from tsung (tsung is the testing framework) graphs, there TCP ...
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63 views

Are all internet file downloads using FTP protocol?

I heard, FTP is used to transfer files over a network. Also heard that it uses TCP port 20 and 21. So TCP is connection oriented. We have acknowledgments. If the transmission is lost, we should be ...
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4answers
624 views

Can't host any server, ports blocked from external requests by accessible via LAN

I am running a Minecraft server hosted at TCP 25565 which I can access via LAN, but cannot be reached externally. I am not using any router and it is connected to an RG-Box Allied Telesis ...
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82 views

How can I fire many HTTP requests using a single TCP connection?

I would like to know if there is a way to open a single TCP connection to a server and request several pages over HTTP on that connection. Is there a way to do this using common Linux client tools?
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61 views

Why is it possible to continue working in a ssh session after a network disruption?

What enables the Secure Shell client and server to resume communication after one or several network interfaces in the communication path between them is shut down and re-appears some moments later? ...
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1answer
77 views

Simple program to turn a server into a client and vice-versa?

What would be a simple to use program for Windows that would do the following: Computer A unknown TCP client wants to connect to computer B's unknown TCP server. Both are behind a NAT. Computer A ...
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1answer
36 views

Filter outgoing connections but allow incoming

I a computer on my local network that I want to have accessible from any computer on the local network as well as from the internet, but I don't want it to be able to connect to other computers. I ...
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2answers
136 views

Monitor Application Network Activity

I use TCPlogView to see all tcp activity of a software. for example: An app (sample.exe) downloads this file in background: google.com/dl/sample.txt when I track it with a TCP software I see this: ...
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What is “armtech daemon”?

I ran a netstap -p tcp on my machine (A macbook) and noticed a number of entries for something called localhost.armtechdaemo. Searching the web doesn't really give me anything useful. Does anyone ...
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548 views

have tcpdump show the 'conversation' as i would get from wireshark?

Is it possible to get the same output i would get from: tcpdump port 80 -w log.pcap wireshark log.pcap in wireshark Analyze > Follow TCP Stream and then in the bottom drop down Entire ...
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133 views

Load TCP New Reno protocol

I am doing some test of the congestion control protocols and I cannot find how to load the protocol New Reno. I loaded a lot of protocols like Reno, Vegas, Hybla, Bic, Cubic, etc using the sysctl ...
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Is it possible to suspend a socket (SSH session, specifically) to switch network devices?

When resuming a tmux workspace on my laptop, I regularly have to decide between the wired and WiFi connection. Ethernet has very low latency, but forces me to reconnect any time the laptop is moved. ...
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1answer
2k views

Wireshark - How do i filter the TCP[RST] packet?

I am looking for filter out the TCP[RST] packets on wireshark. I have tried tcp.analysis.flag but it didn't help.
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218 views

Firewall is blocking echo request on port 7 (TCP)

I have an app which needs to receive a message back from the server. With the firewall on, I do not get the message back. If I turn off the firewall I get the request back. I have added some rules ...
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1answer
5k views

Windows 7 firewall causing remote connection to time out; should refuse connection

The Windows 7 Firewall is running with default options to allow outbound connections and block incoming connections. I have a process trying to connect regularly from within my local network, which is ...
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355 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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345 views

How does a proxy know where to forward the requests to?

When a proxy receives a connection how does the proxy know where to forward the request to? For example in Java we can set a system property for proxy. So we set the IP of the proxy and the request is ...
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3answers
805 views

Network Traffic per process/application windows

I know that there are plenty of applications to do this (like procexplorer) but is there anyway to access the winapi (what method/reference is used) to retrieve the network traffic (TCP, UDP, etc) per ...
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150 views

Data corruption after upgrading broadband speed and modem/router

I'm using an ISP called Fibertel in Argentina, and I recently upgraded my connection to 30 down/3 up. With this change came a new modem+router: the Motorola SBG 6580. Before I had something like 1 ...
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TCP/IP on the transport level

I'm trying to understand what happens when I send a packet using a socket on the transport level. Do all packets which leave my computer go first to a geographical location designated by my ISP? Then ...
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1answer
257 views

What type of TCP connections are counted?

In Windows 7's Resource Monitor, in the TCP Connections graph at the top right -- how are those connections being counted? Does a "listening" state count, for example? Does it matter what state a ...
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2answers
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TCP: Maximum number of connections (client and server)

In the description of TCP in the Wikipedia, it is stated that The number of sessions in the server side is limited only by memory and can grow as new connections arrive, but the client must ...
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273 views

why TCP window scale values (scaling factor) are different in different hosts?

why TCP window scale values (scaling factor) are different in different hosts? why not make this value the same on all hosts? in theory, this value is between 0-14. what is the practical range for ...
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366 views

Are there any requirements for the sequence numbers on TCP Reset packets?

If there is a TCP connection between TCP program A and B, and its source IP address/port and destination IP address/port are known by an attacker, now the attacker wants to send a TCP Reset packet to ...
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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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TCP video streaming: TCP throughput(rate) and RTT

we know that a rough estimation of TCP rate is: WINDOW/RTT, where WINDOW is the min(CWIN, RWIN), CWIN is the congestion window size of the sender, while RWIN is the receiving window. nowadays, the ...
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TCP SYN does not reach TCP server

I have a TCP server listening on 10.10.10.101, port 2000, running on a Windows 7 machine. Below is the corresponding output line for the command netstat -aon: TCP 10.10.10.101:2000 0.0.0.0:0 ...
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Find processes listening on the wildcard address in `lsof`

Using lsof, I can find all of the processes with a TCP socket listening for connections: lsof -Pni -sTCP:LISTEN e.g.: COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME cupsd 662 ...
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581 views

Why does TCP sometimes not acknowledge the packets it receives?

I use firefox to visit a web server running on a computer on my LAN. I notice that sometimes TCP doesn't acknowledge the packets it receives. For example, in the following captured packets: ...
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3answers
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How exactly does a proxy work?

If I want to connect to say, IP 100.100.100.100, Port 80, my computer will send a tcp packet with this adress into the wire. Now If I use a proxy server say, 200.200.200.200 Port 8080 (such kind of ...
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2answers
5k views

TCP Slow start and congestion control, and how to modify them

I'm trying to change the behavior of the tcp slow start protocol on a CentOS5 box (uname -r => 2.6.18-238.12.1.el5). I have read that the following command will change my icwnd to 8: ip route change ...
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2answers
3k views

Detect what outgoing ports are bypassed by firewall

My school has a firewall which limits most outgoing ports. There're only TCP/80, TCP/443, TCP/21 allowed. Is there's a way to find out all the outgoing port allowed by the firewall? My current idea: ...
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969 views

Open TCP port in Windows 7 and read incoming data, what program to use?

I have an external device which can connect over GPRS to the Internet using a SIM card and I want to see what data it sends. I can program it to use my computer as a server and then use a program to ...
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1answer
414 views

about combinations of TCP flags

TCP FIN packet, ACK flag is always set? In TCP tear-down phase, there are usually 4 packets: FIN/ACK, ACK, FIN/ACK, ACK. Is it possible some of these packets may not be sent by a TCP peer? When there ...
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313 views

TCP: when in TIME_WAIT state, will TCP starts a new 2MSL time if it receives a retransmitted FIN with 2MSL

we know that when a TCP program is in TIME_WAIT state, it waits for a FIN for 2MSL. if it receives a retransmitted FIN with 2MSL and retransmits an ACK, will it starts another 2MSL timeout or not?
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256 views

How to intentionally delay TCP packets in one direction

I've looked at this already: How to deliberately introduce a delay for incoming UDP packets I am testing a server-client system, and need to delay messages from the server to the client by some ...
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196 views

Disable tcp slow start

I am looking for disable tcp slow start mechanism for high-speed network. Currently clients send 100MB flows to random servers with non-blocking 1Gbps link. In my math, the completion time of the ...
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736 views

TCP header option: SACK-permitted (Selective Acknowledgments) negotiation

I'm doing a research project, which needs to split tcp connection. so I have some pecular questions, which may happen in my development. The problem is understanding of TCP SACK-permitted ...
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if a TCP packet got partially acknowledged, how will the retransmission mechanism react?

if a tcp client send a packet, with sequence number from 10000 to 20000, to a tcp server. the tcp will respond with an ACK with seq_ack 20001. if I intercept the TCP packet from the client, and ...