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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Using socat to Tunnel/Proxy TCP want to split send/receive into separate files

I'm using socat to dump plain TCP (e.g. HTTP) traffic: socat -v tcp-listen:$PORT,reuseaddr,fork,keepalive tcp:$TARGET_HOST:$TARGET_PORT At the moment all send and receive traffic is dumped into ...
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2answers
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Distinguish TCP server from client within netstat output

I have a socket connection between a client process and a server process, both running on my machine. There are two entries shown for the connection as, sudo netstat -ntp | grep 56442 tcp 1 ...
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1answer
323 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 ...
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1answer
62 views

TCP Westwood implementation available?

Is there a way to install TCP Westwood congestion control algorithm module for FreeBSD? If not, maybe there's a source code available that could be compiled into a loadable Kernel module? Thank you ...
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0answers
43 views

Difference between MTU for a route and MTU for an interface

There is a server I connect to over the WAN and somewhere over the route there is packet loss unless I set the interface MTU to 600: ifconfig eth0 mtu 600 Doing this causes problems with ...
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1answer
653 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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3answers
11k views

Killing tcp connection in linux

I have some dead connection in one application which is in hanged state if client machine is dead. ->192.168.1.214:49029 (ESTABLISHED) Is there a way to terminate these option from linux ...
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3answers
112 views

How to create a TCP listener?

Introduction: I have created a bash function that is able to check whether a port is available and increments it by 1 if false until a certain maximum port number. E.g., if port 500 is unavailable ...
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1answer
43 views

Effect of limiting tcp connections through iptables to limit ssh sessions

I have limited no. of tcp connections through iptables to limit total number of ssh connections. Now when i am adding a rule with maximum limit of tcp connections lesser than currently opened ssh ...
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4answers
13k views

Logging outgoing connections as they happen

Is there a way to log to file all the outgoing connections that a process creates? I am aware of netstat but that seems to be more of a snapshot of a point in time rather than something that runs and ...
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2answers
52 views

lsof to identify incomming TCP connection

I which to know if my server establish a connection to a remote server or if the remote server tries to reach my server, I try to read the output of lsof and obtain this: lsof -i TCP:25 USER FD ...
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1answer
191 views

Changing the TCP RTO value in Linux

I will like to alter the TCP RTO (retransmission timeout) value for a connection, and some reading I have done suggests that I could do this, but I don’t where and how. I have looked at the ...
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39 views

Transparently Relay TCP Socket to Serial Port (and vice versa)?

I would like to create a psuedo serial device (such as /dev/ttyXXX0) that I can use to make transparent serial connections to an arduino that's on my wifi (via an esp8266 serial bridge). I would like ...
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1answer
55 views

Meaning of 'netstat -anto' output

I did netstat -anto and got following result: Proto Recv-Q Send-Q Local Address Foreign Address State Timer tcp 0 0 127.0.0.1:1169 ...
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2answers
55 views

Linux kernel parameter “net.ipv4.tcp_workaround_signed_windows”

I am seeing some intermittent network issues when sending large amounts of data over a network and it has been suggested to me that setting this option to a 1 may possibly resolve the issue. ...
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2answers
140 views

Different Congestion Control algorithms in FreeBSD

Is there a way I can run a different (than the default) TCP congestion control algorithm in FreeBSD? I am trying to modify an existing TCP congestion control algorithm with some ideas published in ...
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1answer
37 views

What ports will an ssh daemon use outbound?

I am making a bastion ssh server. When I use the following rules in its ip tables, I am able to connect to the server just fine: Inbound Rules Allow traffic on port 22 from my client's IP Block all ...
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6answers
29k views

Linux: allowing an user to listen to a port below 1024

I need to allow an user (different from root) to run a server listening on port 80. Is there any way to do this?
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0answers
51 views

Netstat command lists only 256 connections when I do SYN flood on my server

I have been trying to do SYN flood on one of my servers from an other machine. And I am sure that I causing a DOS on it, but it actually shows only few connection. That is when I type netstat -a | ...
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1answer
90 views

socat duplicate stdin to each connected client

ncat (from the nmap folk) has a neat default action of duplicating any input to all connected clients. E.g.: Start a server on terminal 1: % mkfifo messages % exec 8<>messages # hold the fifo ...
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3answers
306 views

Tool to generate TCP traffic

I want to generate a TCP traffic starting from the port 0 to the port 65535. 1 tcp packet for each port with 1ms between 2 packets. The generator should not care if there is a TCP ACK or not. Are ...
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2answers
66 views

Binding two incoming TCP connections

I have a client to connect multiple devices. For not paying monthly static IP fee per device. We plan to change the architecture. In this new architecture devices connect to a server. Instead of ...
16
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2answers
55k views

Orphaned connections in CLOSE_WAIT state

I've got a SLES machine that accumulates TCP connections in a CLOSE_WAIT state for what appears to be forever. These descriptors eventually suck up all available memory. At the moment, I've got 3037 ...
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53 views

How to enable Tcp\Ip remote connections in Centos 7.0

I am running Centos 7.0 using VMPlayer . I have set a private network shared with the host (Windows 7) . On my Centos Server i have opened a tcp listener on port 10102 . I could not connect to this ...
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1answer
33 views

How to enable SYN Cookies on Debian 7.5?

How do I enable SYN Cookies on Debian 7.5? nano /etc/sysctl.conf #net.ipv4.tcp_syncookies = 1 remove here the # sysctl -p service network restart Is that the correct way? Or what must I look ...
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1answer
28 views

Unexpected netstat output in DNAT conditions

So, here I have a basic setup with SOCKS5 proxy listening on, oh, say 8123 I redirect TCP to the proxy via iptables From iptables perspective everything looks peachy, iptables -t nat -v -L shows ...
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373 views

D-Bus authentication and authorization

I'm trying to set up remote access to D-Bus, and I don't understand how authentication and authorization are (not) working. I have a D-Bus server listening on an abstract socket. $ echo ...
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84 views

What does an inode for a socket contain?

I read somewhere that the inode for a TCP socket would contain the buffer space. Is that true, and if so, does it mean that the inode contains a memory address for the buffer space used by the ...
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1answer
6k views

Is it better to set -j REJECT or -j DROP in iptables?

There's an example of iptables rules on archlinux wiki: # Generated by iptables-save v1.4.18 on Sun Mar 17 14:21:12 2013 *filter :INPUT DROP [0:0] :FORWARD DROP [0:0] :OUTPUT ACCEPT [0:0] :TCP - ...
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1answer
51 views

check tcp packets reception below tcpdump level

I am having an issue with my smartphone device and packets monitoring: I am trying to find a reason why I cannot establish a VPN connection via PPTP protocol. I have the following successful ...
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1answer
51 views

Linux drop packets if received from another equipment

Problem description : When I establish a VPN connexion between a VPN client and my home server, if the connexion are both across my firewall (pfSense) or are established directly, the connexion is ...
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votes
2answers
14k views

Fast way to copy a large file on a LAN

I am having some trouble with NFS, and I'd like to try using just plain old TCP. I have no idea where to begin, though. Hardware-wise, I am using an ethernet crossover cable to network two netbooks. ...
0
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1answer
133 views

How can I edit /proc/net/tcp?

I need to edit 1 line in /proc/net/tcp while the file is also used by the linux kernel for updating other lines of it by the kernel. Background: Each line in /proc/net/tcp represents a TCP socket. ...
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1answer
100 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
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1answer
30 views

What happens to TCP when a write fails to enqueue with the device tx ring?

Lets say the device tx ring is full and you do a normal C non blocking write(fd, buff) to enqueue data in the TCP SND buffer. What happens when this fails? In UDP - the packet would be dropped but ...
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0answers
36 views

How much of Linux's recent TCP bufferbloat remediation also applies to SCTP?

I am looking at rebuilding an existing communications sub-system within a shared-nothing cluster. The current message protocol is built on UDP but layers on reliable, in-order delivery and ...
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2answers
205 views

tcpdump captures network-wide UDP traffic, but not TCP

When observing traffic with sudo tcpdump udp, it behaves like it should: I can see all traffic which is happening in the network, even when the machine which I am using is not involved. However, when ...
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votes
1answer
60 views

Close the neccessary Ports [duplicate]

I am using Linux Mint and I am newbie. Someone is trying to access my computer via my MAC Address and open port. I have some questions: I know that there are different type of port like TCP and UDP. ...
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92 views

Linux, dev/tcp validation and kill the process with timeout

I have this part of code, I need to validate if the connection was ok or not, AND, if the process is running more than 3 seconds, it will be killed. But, I dont know how to keep the value of the ...
2
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1answer
349 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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votes
0answers
169 views

Opening a TCP port in Linux

I am trying to establish a TCP socket between my linux server and my client running on my laptop. The TCP server code I am running is, from socket import * HOST = '' PORT = 1999 ...
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votes
1answer
237 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
85 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
149 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 ...
0
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0answers
47 views

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
66 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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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 ...
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1answer
55 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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votes
4answers
3k 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
138 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 ...