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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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 ...
2
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1answer
66 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 ...
0
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3answers
70 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 ...
0
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0answers
19 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
33 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: ...
0
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0answers
49 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 ...
1
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0answers
27 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 ...
18
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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 ...
0
votes
1answer
53 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 ...
0
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2answers
67 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 ...
0
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0answers
28 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 ...
2
votes
1answer
89 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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0answers
68 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 ...
1
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1answer
155 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: ...
-1
votes
1answer
48 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 ...
0
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0answers
60 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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0answers
89 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 ...
2
votes
1answer
133 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
62 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 ...
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0answers
41 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 ...
0
votes
1answer
18 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 ...
3
votes
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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2answers
352 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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2answers
50 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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2answers
44 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 ...
1
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1answer
71 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
votes
1answer
58 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 ...
1
vote
1answer
35 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 ...
6
votes
1answer
330 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: ...
2
votes
1answer
134 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 ...
2
votes
2answers
119 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 ...
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0answers
38 views

Can spawn-fcgi be user for tcp/udp server

Spawn-fcgi by lighty labs It only uses unix socket functions socket(), bind(), connect(), listen(). Is it possible to use it not for FastCGI server, but TCP or UDP server?
1
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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
votes
1answer
60 views

Down single connection

There are many connections to the external interface(s) on the specified port e.g. ![netstat |grep 1521][1] tcp….1540….…0 172.17.40.33:36791……..172.17.40.90:1521…….…..ESTABLISHED tcp….1540….…0 ...
2
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0answers
50 views

Exclude a loopback interface or address from processes listening on the “any” address

I'm trying to create a setup where I can connect to some service running on a host only reachable through a SOCKS proxy by the host's actual name and the port the service actually uses (so that ...
1
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2answers
247 views

Drop TCP packets and prevent TCP retransmission

I have an application that sends TCP data to a server. My server is made to intentionally drop the packets sent by the application, and as a result the client retransmits the packets. I need to ...
3
votes
2answers
85 views

How can I determine what program or user connected to a particular port after the fact?

I am examining the egress IPTABLES log of my computer for yesterday and notice the following: IN= OUT=eth0 SRC=192.168.1.1 DST=69.46.36.10 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=12345 DF PROTO=TCP ...
1
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2answers
318 views

How to troubleshooting failing ping to router on a linux box?

I have a home network 192.168.0.x from which I am posting this message, on this network I have a CentOS7 host 192.168.0.3 which is running a DNS server for the network. I can ssh into 192.168.0.3 I ...
3
votes
1answer
81 views

Force application to use specific port on Fedora machine

I have an application on my fedora machine that sends SIP TCP requests to the server. The application chooses a random source port to send the requests. Is there some way I can force the application ...
1
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0answers
118 views

Rsync - Corrupted MAC on input

Background I have a script on my NAS which is a Synology DS212J which is running on a special distro where uname -a gives me Linux DS212J 2.6.32.12 #4493 Wed Jul 16 11:37:16 CST 2014 armv5tel ...
0
votes
1answer
17 views

tcpdump Filter with certain file types?

I use the unix command tcpdump with these extensions -A -s0 -ien0 port 80 I know how to add, for example a new host, that would be and \ host random.com Can I sniff for certain filetypes? I have ...
4
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6answers
712 views

How do I work out which port to log in on with SSH?

I have an Ubuntu 10.04 server setup remotely that I setup a while back. While I recorded the username and password, I seem to have been clever and changed the usual ssh port from 22 to... something ...
3
votes
1answer
157 views

Allow non-root unmodifiable sofware to bind to ports 80 & 443

The company I'm in uses the Java Secure Application Manager to "secure" non-internal connections their webmail and electronic collaboration software. Aside from using expired certificates, and ...
1
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1answer
59 views

Analyzing network traffic

I want to get a good overview what kind of network communication is going on on my computer. One way would be starting wireshark, which is fine for very low-level problems but is quite cumbersome to ...
2
votes
1answer
1k views

Kill any service running at a specific port

I am trying to write a script that kills service running at a specific port. This is my script: a=$(ps ax | grep 4990 | grep java | awk '{print $1}') kill -9 $a It's a java program. This script ...
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0answers
264 views

tcpdump not capturing http or tcp/ssl traffic

I have been trying to learn tcpdump and I am using this command to attempt to monitor my network: sudo tcpdump -I -i en1 But this gives me a bunch of stuff I don't want, so I used this version to ...
2
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1answer
193 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 ...
23
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5answers
4k views

How to close ports in Linux?

I have some question in closing port, I think I got some strange things. When I use execute nmap --top-ports 10 192.168.1.1 it shows that 23/TCP port is open. But when I execute nmap --top-ports ...
4
votes
1answer
474 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 ...
2
votes
1answer
419 views

how to connect ssh 'with' specified port?

I know how to connect 'to' a certain port when ssh'ing. ssh user@remotehostip -p XXX but is there a way to establish a ssh 'with' a certain port? I mean, is there a way to specify the port which ...