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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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
39 views

ubuntu IPTables

I started hosting my game-server on Ubuntu Linux 14.04 I am having an issues ، some enemies/bug abusers log in 2+ characters in the same second then they spam a certain spell/word that lags/stops my ...
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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 ...
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0answers
17 views

Why select do not tell me that a client wants to connect? [migrated]

I've made a simple tcp server that I can test with telnet program. When running it on windows, it works as expected, when running it on linux, the behavior is strange: telnet clients understand ...
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0answers
24 views

Netid in ss output is confusing

I'm on an Ubuntu 14.04 x64 machine. I have something running on port 51236 and I want to know whether it's TCP or UDP. So I ran ss -an | grep 51236 and got the following output. tcp ESTAB ...
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0answers
17 views

Half-close netcat connection

How can I have a netcat connection terminate the sending half of a TCP connection if its input reaches EOF? I have a (non-standard) TCP service which reads all its input (i.e. until the client sends ...
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0answers
10 views

Changing the Retransmisson Timeout (RTO) estimation in Fedora

Retransmission Timeout(RTO) in a TCP plays a vital role in the internet. There are many algorithms proposed for calculating the Retransmission timeout. RFC 6298 is used for the estimation of RTO. I ...
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0answers
34 views

nginx server never resolves

I have set up an nginx server which is a proxy for port 80 to http://127.0.0.1:3000, but the request never gets through. It just infinitely loads. I have tried sudo /sbin/iptables -I INPUT -p tcp -m ...
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0answers
27 views

Cannot access server outside of server`

I have a node server listening on port 80. If I send a request to it like this: request('http://127.0.0.1:80',function(err,res,data) {console.log(data)}) It works. It returns what I would expect. ...
7
votes
4answers
20k 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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0answers
8 views

Claiming node on swiftstack times out

I am trying to connect a node that I have installed CentOS on using SwiftStack. To make this connection, both port 443/TCP and 1194/UDP will need to allow outgoing traffic on your firewall. I have ...
0
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0answers
18 views

WARNING: at net/ipv4/tcp.c:1654 tcp_recvmsg

Our Linux based device (3.7.2) experiencing following issue when we try to do FTP or SCP over WiFi Connection. Same will work on Ethernet Connection or on TFTP. Here is the dmesg log for this issue: ...
0
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1answer
53 views

pfsense tcp connection between openvpn and lan is broken

I am trying to connect openvpn clients into an internal lan, so they can access a http server. pfSense as well as my http server are running on a virtual machine of my home proxmox node. Both are ...
6
votes
4answers
245 views

Writing a TCP server in bash

So, I recently found out about how you can send TCP packets through the /dev/tcp/hostname/port file, but my main problem here is how I receive them. I want to make a bash script that can host a TCP ...
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vote
2answers
75 views

How to know if port 25 is blocked?

I am running Debian Jessie 8.1. The VPS provider says that port 25 is open. However, when I installed Rainloop and am not able to use it with the System users. Under the RainLoop admin panel I went ...
1
vote
1answer
29 views

Can nmap display only hosts with specific ports open?

Can nmap list all hosts on the local network that have both SSH and HTTP open? To do so, I can run something like: nmap 192.168.1.1-254 -p22,80 --open However, this lists hosts that have ANY of ...
0
votes
2answers
36 views

Unable to connect remotely to custom application

I've built an application that listens on the localhost address and a specific port, lets say port 11001. Its on a remote machine with CentOS. I currently have a python script on my local machine that ...
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0answers
17 views

is it possible to read a process's incoming TCP RecvQ?

I have a process running which has a number of incoming TCP connections, all of which show a non-zero RecvQ bit for some reason the process has not gone to read the incoming data. netstat -nap ...
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1answer
38 views

Netstat Listen Queues

What information can I gather from netstat listen queues? Looking at the man page I can see that using "-L" in netstat it shows me the size of listen queues. It tells me information about each ...
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0answers
13 views

Can't get websocket- answer from client browser in gawk

I want to make websocket server with gawk. I can pass handshake and send many messages to client, but when i'm trying to listen host to get client's dataframe gawk stops and cant do it. What i'm doing ...
0
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0answers
7 views

how to remove Queue in send_Q-part of netstat?

I have a tcp-server or may be it is lazy tcp-server because sometime the program dose not take the data from socket and i see some number is send_Q/recv_Q column of 'netstat -tn' command. is there a ...
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vote
1answer
48 views

Delay FIN-ACK sent on linux

For a project I need to delay the FIN-ACK sent in an SSL connection on Linux. Is there any way to do this? I can send an https request by using curl https://www.google.com, but how do I modify the TCP ...
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0answers
13 views

How to limit my bandwidth at linux? [duplicate]

which parameter I need to configure at "ls /proc/sys/net/ipv4/tcp*" to limit my bandwidth to receive less packages from my TCP connection?
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0answers
40 views

SIGSEGV: 0x0000000000000000 in ?? ()

I am executing an iperf connection between two UML machines running the following kernel: Linux client 4.1.0-ga61e56d #55 Mon Nov 30 13:51:59 CET 2015 x86_64 GNU/Linux I am working on the TCP/IP ...
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2answers
42 views

tcpdump bassed datalogger

I am building a datalogger with raspberry pi. I have used a Shell script in rc.local, I am capturing the bytes using tcpdump. The Problem am facing is that the log file is getting replaced each and ...
0
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3answers
320 views

open port 8080 for listening

My question is very simple, how can I open 8080 port for listening? In normal situation, I have tomcat7 that listens on port 8080. sudo netstat -tanpu | grep ":8080" tcp6 0 0 ...
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5answers
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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 ...
10
votes
1answer
629 views

/dev/tcp not found

When I try to run the following command: echo -e "GET / HTTP/1.1\n\n" | /dev/tcp/74.125.225.19/80 I get the following error message: bash: /dev/tcp/74.125.225.19/80: No such file or directory ...
27
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3answers
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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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votes
4answers
101 views

Is any solution to make interactive TCP/UDP server under Linux?

I need some tool like this one for Linux. I need not a GUI (i.e. GUI/CLI -- this is not so important), but I need to be able to make a server which can listen at any port, receive and send a raw (i.e. ...
1
vote
1answer
29 views

How do I store the data in disk directly in kernel module? [closed]

I capture the TCP packet in function of netif_receive_skb , I want to store the playload of TCP packet. we can't read/write the file in kernel module, so store in disk directly maybe a way? ...
0
votes
1answer
49 views

How to load balance mutiport traffic using HAProxy

I have 2 servers that host an application that listens to mutiple ports. Is there a way to load traffic between these servers using HAProxy? I tried this in configuration, but it didn't work: ...
0
votes
1answer
55 views

How to force TCP packets to use a specific NIC

My Linux (kernel 3.17) computer has more than one NIC: eth0, eth1, (and/or eth2...) I have several PC connected to each of them: PC0 <---> eth0 (192.168.1.100) PC1 <---> eth1 ...
0
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0answers
246 views

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

I would like to create a pseudo 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 ...
2
votes
2answers
339 views

How to use lsof to identify incoming TCP connections?

I want to know if my server establishes a connection to a remote server or if the remote server tries to reach my server. I tried to read the output of lsof and obtain this information: lsof -i ...
4
votes
1answer
80 views

Why are IPv4 TCP connections showing as tcp6?

Here's the output of netsat -tupn on my Debian Jessie server: Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program ...
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0answers
103 views

does NFS overrides TCP keepalive time?

NFS server somehow disconnect NFS client detect server is disconnected client tries to reconnect server reappears and reconnect successfully it seems that TCP keepalive, connection timeout is ...
3
votes
1answer
38 views

How to call lsof properly to retrieve all TCP connections?

# lsof -n -itcp | wc 92 919 10212 # lsof -n | grep TCP | wc 2482 27222 373861 What I'm doing wrong with lsof -itcp ? Such calling is skipping part of connections, looks like this ...
2
votes
1answer
320 views

Why do I have Established TCP connections with no owner PID?

Both ss --processes and netstat --program (with sudo) list some ESTABLISHED TCP connections to local port 6514 with non-zero Recv-Q values and no owner process (netstat output shows - where ...
14
votes
4answers
2k views

TCP dies on a Linux laptop

Once in several days I have the following problem. My laptop (Debian testing) suddenly becomes unable to work with TCP connections to the internet. The following things continue working fine: UDP ...
2
votes
1answer
35 views

Alternative of ArpRetryCount in CentOS

ArpRetryCount Implemented by Microsoft and the following is its descritption : Determines how many times TCP sends an Address Request Packet for its own address when the service is installed. ...
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1answer
39 views

Iptables dropping HTTP 302 packages contain suspicious domain string

The HTTP 302 packages I want to block have: Header HTTP/1.1 302 Found Location: ...
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0answers
83 views

How to download a video from rtmp protocol from behind proxy using rtmpdump

I am trying to download video from rtmp://flash.dce.harvard.edu/bounce/mp4:2015/01/14328/L01/14328-20140902-L01-4-h264-av1248-16x9-852x480.mp4. My college internet runs behing proxy, Is there a way I ...
12
votes
3answers
19k views

How do I reserve ports for my application?

How do I reserve a list of ports for my custom applications? To be specific, the product I'm creating has a lot of processes and a lot of intercommunication between them. The problem I'm having is ...
4
votes
1answer
139 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?
2
votes
1answer
2k views

Changing the TCP RTO value in Linux

I want to alter the TCP RTO (retransmission timeout) value for a connection, and some reading I have done suggests that I could do this, but does not reveal where and how to change it. I have looked ...
2
votes
2answers
35 views

Using remote XServer

I recall seeing a tutorial on setting up Xorg to be a vnc replacement without installing anything, but I cannot find it. I was hoping someone here could help out. Scenario: Machine A no monitor ...
0
votes
0answers
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How do I increase my network perform on Centos 7

I am doing some research and I find that I have to configure the sysctl.conf file if I want to increase the network performance. So, I want to configure the default maximum Linux TCP buffer sizes ...
31
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7answers
38k 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?
1
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1answer
251 views

Read “/proc” to know if a process has opened a port

I need to know if a process with a given PID as opened a port without using external commands. I must then use the /proc filesystem. I can read the /proc/$PID/net/tcp file for example and get ...