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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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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53 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 ...
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25 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
10 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
17 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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34 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
35 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
35 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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40 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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1answer
65 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
17 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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1answer
81 views

Different Congestion Cotntrol 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
43 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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2answers
122 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 ...
2
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1answer
51 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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20 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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33 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 ...
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3answers
126 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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1answer
130 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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78 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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1answer
65 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
72 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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27 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
34 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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1answer
42 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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1answer
83 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
254 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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47 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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118 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
62 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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0answers
43 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 ...
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1answer
227 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
127 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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39 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
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1answer
257 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
76 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
345 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
107 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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105 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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171 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
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1answer
346 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
votes
0answers
80 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
votes
1answer
68 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
27 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
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1answer
104 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
811 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
82 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
64 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
104 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 ...