The Transport Control Protocol (TCP) is a low-level part of the protocol stack used by the Internet. It sits directly above the IP layer and is responsible for making sure that dropped packets are resent.

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Create new TCP Connection for every http requests in Python [migrated]

For my college project I am trying to develop a python based traffic generator.I have created 2 CentOS machines on vmware and I am using 1 as my client and 1 as my server machine. I have used IP ...
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1answer
501 views

How to investigate a random reset on TCP client port connected via loopback interface to a server

I have a test suite which initializes a server on the localhost and then runs thousands of stress tests which include starting and stopping clients connecting to this local server on same machine. I ...
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1answer
210 views

Socksifying a qemu-kvm using tsocks

I'm trying to socksify a qemu-kvm using tsocks, but I have no success. I don't know if qemu access directly the hardware, skipping the OS or something like that, but I wasn't able to do this feat. ...
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1answer
35 views

Test for open TCP port in bash script

I want to delay the script execution until a certain server process is ready, which it is once it accepts incoming TCP connections. How do I test if a local TCP port is open (I get a SYN/ACK answer)? ...
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1answer
48 views

How to artificially open many tcp connection on a host (testing)?

I'm trying to build a test setup which test my server's performance under high load. In order to do that I want to open thousands of tcp connection. The problem is that I only have two hosts, one is ...
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why do I have so many open socket handlers and netstat DGRAM entries?

I run on a RPi (Raspbian 3.12.35+ #730 PREEMPT Fri Dec 19 18:31:24 GMT 2014 armv6l GNU/Linux) a daemon in Python 2.7.8 which queries various APIs via requests and provides itself an API for another ...
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1answer
19 views

Transparent proxying of TCP connections on port (mostly, without root access)

I have the Client machine living somewhere on the Internet, and it needs to access a custom port of Target machine (or, initially any port on any reachable machine, but, eventually, particular port, ...
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5answers
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How to check whether firewall opened for a port but not listening on the port

We will be deploying a new application to a Server and the application will be listening on port 8443. We have asked Network team to open the firewall for the port 8443 on that server before deploying ...
3
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1answer
36 views

log PID of each connection attempt

Finding the PID of an established connection is trivial using netstat or lsof. However, I have a process which is creating a connection ever 60 seconds to our database and locking it up by maxing out ...
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4answers
2k views

Simple way to create a tunnel from one local port to another?

I have a development server, which is only accessible from 127.0.0.1:8000, not 192.168.1.x:8000. As a quick hack, is there a way to set up something to listen on another port (say, 8001) so that from ...
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1answer
71 views

Linux: monitor my own internet usage page by page

I have a monthly broadband subscription which rolls over on the 23rd of each month. I had arrived near the end of my usage so I was carefully checking that I didn't go over my limit - they crucify you ...
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3answers
103 views

Simple TCP server listening on a port but not returning SYN-ACK

I am looking for a command-line TCP server (preferably a one-liner), that will listen on a specified port and when received SYN, it will not respond with SYN-ACK as usual TCP servers do. The purpose ...
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41 views

telnet connection closes

I am running hdfs in one machine. I am trying to write into hdfs from my second machine. I got connection refused error and got this link in the error itself: ...
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0answers
25 views

cannot change tcp-segmentation-offload

I have been doing tests with tcp-segmentation-offload on and off, but now I cannot seem to change the parameter anymore, it is stuck on "off" (I can change generic-segmentation-offload) ...
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0answers
52 views

How to check number of connections

My server have high loads. CPU usage is low. Memory usage is low. IO is low. So I improve maximum number of connections in cpanel. Things are working. However, where can I see detail? How do I ...
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6answers
44k views

Determining what process is bound to a port

I know that using the command: lsof -i TCP (or some variant of parameters with lsof) I can determine which process is bound to a particular port. This is useful say if I'm trying to start ...
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2answers
3k views

Using tcpdump to extract NFS RPC contents

Fairly simple question... I'm running tcpdump and trying to analyze the contents of the TCP packets between server/client. I see the "GETATTR" RPC being received, which is great! However, I want to ...
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0answers
30 views

How can I log outgoing TCP traffic including the full path of URLs?

I use a program regularly on Linux that makes a TCP request when it starts up and updates a file with an access token before launching. I'd like to write a batch script that makes this request (using ...
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2answers
1k views

Is it possible to connect to TCP port 0?

Listening to TCP port 0 allocates me a free port number on the system. But what happens when I try to connect to TCP port 0? The obvious answer is: "It doesn't work": $ nc localhost 0 ...
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1answer
96 views

Which port to open for Google HangOut Video Conference

We need to open the necessary ports for Google Hangout VIDEO Conferencing in our firewall. Unfortunately my netmon trace shows Port 51355 and 51336 to be active; which is not at all what the Google ...
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2answers
148 views

Using Wireshark on Linux to observe coupled HTTP-request and HTTP-respond

I use Wireshark on Linux to observe my HTTP traffic. Other programms like Firefox Live Http Headers show coupled http-request from my browser and http-respond from any server. How using programs like ...
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2answers
84 views

Runs perfectly through the command line, will not work through systemd ExecStart

I've installed Butterfly http terminal server, written in python, on my Arch machine. I'm new to systemd, but I'm having an issue with one of the command line parameters. /usr/bin/butterfly.server.py ...
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0answers
32 views

How can I reduce the TCP connection time for web resource requests at the OS level?

I'm experiencing an issue where almost every request for a resource on a web application has a 100ms - 500ms delay in the "connecting" phase as reported by firebug, which is the time it takes to ...
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0answers
69 views

TCP, UDP, etc. works, HTTP(S) does not

I have been trying to set up Debian Jessie on an old Dell Inspiron 300m. Right now the problem I have is, the ethernet connection only works partially. ICMP works. I can ping IPs and FQDNs. UDP ...
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1answer
109 views

nfs mount works for tcp but not over udp

I'm connecting my raspberry pi (raspbmc) with my synology nas. I have 2 mounts 192.168.0.5:/volume1/video /mnt/video nfs udp,intr,noatime,rsize=32768,wsize=32768,nolock,nfsvers=3,async ...
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1answer
204 views

MPTCP doesn't create multiple subflows

I've installed MCTCP in one machine, and tested it in https://amiusingmptcp.com which gave a positive result. Now, when I do iperf -c multipath-tcp.org like they say here I only see one connection: ...
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1answer
62 views

Make TCP to reconnect automatically and quickly

In my Debian Linux system apt-get dist-upgrade is sometimes stalled with [Waiting for headers] message. To make it pass faster I press Ctrl+C and start the command again. How to tune the system to ...
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2answers
5k views

iptables port-mirroring

I need to be able to get a copy of packets received on port 8001 to port 8002. I have tried the following but I get an error that --tee is undefined. sudo iptables -t nat -A PREROUTING -p TCP -s ...
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72 views

different ways how Linux TCP/IP stack terminates connection

I have a Linux machine which connects to SSH server with SSH client(OpenSSH_4.1p1). SSH client machine has IP address 10.10.11.1 and SSH server has IP address 10.10.10.1. SSH client has kernel version ...
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1answer
100 views

Why are these connections not classified as “established” under conntrack?

I have the following rule for iptables: -A OUTPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT such that outgoing connections not classified as established will be logged. Occasionally, the ...
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124 views

Socat execute commands on remote

I am playing around with socat and wanted to execute commands to hosts that connect to my IP PORT running socat. In this case I am trying to dump a file on localhost and this is how I am trying to ...
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2answers
6k views

nc: bind failed: Address already in use

I am trying to execute nc command from a script , my script is executing nc command on different ports of Destination using the same source port. e.g: nc -p 8140 -z -v -n 10.X.X.9 9090 nc -p 8140 -z ...
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1answer
182 views

enable echo service and linux security loophole issues

in order to enable the echo service we need to add the echo lines as the following example : more /etc/inetd.conf echo stream tcp nowait root internal echo dgram udp wait root ...
2
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0answers
65 views

How do I find out how long a socket is in CLOSE_WAIT?

I have a server relatively with a high number of sockets in CLOSE_WAIT I want to know the age of each socket, to know if it's a real problem (sockets not getting closed) or that the sockets are ...
2
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0answers
42 views

Capturing data from a Fluke 1620a via Bash /dev/tcp file descriptor

I am currently trying to develop a script that will connect to a Fluke DewK 1620a Themo-Hygrometer and pull the current temperature and humidity readings from the device. While these devices have a ...
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2answers
50 views

Capturing data from a Fluke 1620a via netcat

I am trying to pull temperature and humidity data from Fluke DewK 1620a thermo-hygrometers and write the temp/humidity readings to a log. I can connect to the device via netcat with a simple 'nc ...
0
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1answer
19 views

Itcpdump output - why is it showing an Ethernet status?

tcpdump -i mlan0 -n tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on mlan0, link-type EN10MB (Ethernet), capture size 262144 bytes Why is this ...
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2answers
457 views

Redirect stdin and stdout to ports

I'd like to take a program P that reads from stdin & writes to stdout, but connect it to nc or whatever such that it reads from a certain port and outputs to another port. # The reading is easy, ...
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1answer
688 views

Port Mirroring in Fedora? [closed]

I have set up an application that listens constantly to a port for network packets, and I would like to create another one that receives the same network packets ( for use as a test bed). Getting the ...
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2answers
51 views

If I send SYN / ACK with one IP and other packets with another, what happens?

I'm learning about UNIX and network programming. I'm not yet sure how to implement this. But I'm wondering: If I forge IP packets of a TCP connection to a server, so that the SYN / ACK packets use ...
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1answer
82 views

Relay server for generic TCP traffic?

Here's my situation: I have a computer (Mac) on a school network that I want to port forward TCP 5222 to for ejabberd, but of course I can't. I have a server at home (Mac with FreeBSD VM) that I can ...
2
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1answer
65 views

bound, but not listening process

python code for simple daemon import socket import time import signal s=socket.socket() s.bind(('127.0.1.1', 20201)) def stop(*a, **k): global work work = False ...
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1answer
40 views

Start a service on a network request (socket activation)

I have a program that under normal activation listens on some port. I don't want the program running continuously. Is there a "quick and dirty" way to wrap the application in a shell script or ...
2
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2answers
1k views

Redirect the default HTTP port to an application

On my CentOS server at mydomain.com, I have an svn web application running on port 8880. I want to hide the port: at this moment, if anybody wants to access, they need to access through ...
2
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2answers
142 views

How to find out how many TCP retransmits are occurring?

I am running Debian Wheezy on an ARMHF platform and do most of the communications over fairly unreliable cell phone networks. Is there a way to read the no. of re-transmits the TCP stack has done ...
2
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1answer
153 views

What are the semantics of getting a EADDRINUSE when no listening socket is bound, but connections are open

Consider a parent process which completes a socket/bind/accept, and will fork children with that socket open for them to communicate with, while the parent continues accepting connections. That parent ...
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1answer
294 views

Networking issue in IBM x3650 after install Ubuntu 14.04.1

I have a problem making TCP connections after a fresh Ubuntu 14.04 installation. First of all, after booting the interface is always off. In my case the interface is manually configured and named em2. ...
2
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1answer
209 views

nc -l in background closes immediately (nc -l 1234 &)

When I put this nc -l 12345 >nc_out in a shell script, run it and then connect from other shell using telnet, it allows me to type some text and have it end up in nc_out. But if I start nc in ...
6
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1answer
340 views

Is there a way to see if process listening on TCP port receives a message?

According to tcpdump, my server receives the following TCP packet: 12:52:29.603233 00:19:e2:9e:df:f0 00:16:3e:6a:25:3f, ethertype IPv4 (0x0800), length 74: 10.10.10.65.38869 192.168.215.82.22: ...
28
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3answers
4k views

Can TCP provide more than 65535 ports?

Is it possible to setup a Linux system so that it provides more than 65,535 ports? The intent would be to have more than 65k daemons listening on a given system. Clearly there are ports being used ...