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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Application Layer PDU size, guaranteed to pass without fragmentation on to the TCP layer below?

I have doubt ! Problem is What is the maximum size of data that the application layer can pass on to the TCP layer below? any size . $2^16$ bytes - size of TCP header I ...
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Does the sequence number of TCP packet headers wrap around?

I was wondering, since the sequence number in a TCP header field is randomly chosen during the handshake and is gradually incremented as packets are exchanged, what happens after 2^32 - initial_seq_no ...
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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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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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Can someone give me full instructions to open ports required by Starcraft 1 [closed]

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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30 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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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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21 views

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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44 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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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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51 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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23 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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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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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
29 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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38 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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3answers
83 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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44 views

How do I find out which process is using up all the TCP connections?

I can only sort by bytes or port or protocol, not number of connections.
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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
47 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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1answer
66 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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39 views

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
29 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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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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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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72 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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32 views

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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2answers
294 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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1answer
108 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
66 views

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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36 views

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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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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131 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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784 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
69 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
202 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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53 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
63 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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112 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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219 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 ...
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1answer
54 views

Wget not getting cookies, not pulling back results in check.

I'm having a couple of issues when porting check scripts between a couple of servers. The script. #!/bin/bash hostname=$1 port=$2 retstatus=0 retStr= st=`date "+%s.%N"` if [ $# -ne 2 ]; then ...
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2answers
72 views

How are Internet connections differentiated from each other by an operating system?

Given this example, how would my operating system differentiate between each request. Let us say I have 3 tabs open, and at the same exact time, they all go to http://google.com. How would my ...
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50 views

How can one redirect to a new host all traffic destined for an old host?

We're moving a bunch of services, say from 1.2.3.4 to 5.6.7.8. In order to test that the new services are correctly configured, we'd like to redirect (to the new host) all traffic destined for the ...
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92 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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734 views

TCP Dup ACK/Retransmission, bad configuration?

I'm currently investigating network issues of a friends LAN (again). The Internet connectivity is very slow and unreliable and sometimes services simply don't work. I've monitored the traffic for ...
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69 views

iptables TCP flags

I'm beginner with iptables and networking so please excuse me for such dump questions. I found in Internet part of filtering malformed packets: /usr/bin/sudo /sbin/iptables -A tcpchk -p tcp ...
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113 views

iptables TCP flags

I'm beginner with iptables and networking so please excuse me for such beginner questions. I found on the Internet part of filtering malformed packets: /usr/bin/sudo /sbin/iptables -A tcpchk -p tcp ...