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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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 ...
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1answer
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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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96 views

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 ...
3
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579 views

graph TCP connection performance based on `ss -i`

A nearby question has brought to my attention the ss utility on Linux, another utility to investigate sockets. It would appear that it may be a great tool to monitor the performance of, say, an ssh ...
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25 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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120 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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198 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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371 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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116 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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195 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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136 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 ...
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298 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 ...
2
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0answers
482 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 ...
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88 views

Why isn't hydra being disconnected?

I have SSHD running on port 5800 on some machine. (It is a my machine at home.) If I run this manually in a terminal: # ssh someIP -p 5800 The connection is lost because I am disconnected after 3 ...
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20 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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41 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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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 ...
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106 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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75 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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104 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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107 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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567 views

Improving TCP performance over a gigabit network

I have two machines both network cards speed is 10Gbps. The inbound bandwidth between the two machines is 10Gbps, the outbound bandwidth internet bandwidth is 500Mpbs. Both machines are using public ...
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362 views

Command for finding open ports

On my linux servers I have this alias set: alias ns="sudo lsof -Pi|grep -v ESTABL|grep -v CLOSED|grep -v -e '->' | tr -s ' ' '\t' | awk '{print $3 "\t" $8 "\t" $5 "\t" $9 "\t" $1}'| column ...
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630 views

How to redirect/forward between a tun/tap device and a socket using linux tools?

I have a socks5 proxy that is bind to eth0. It opens two ports, Port1 is used to connect to remote (for example a http server), Port2 is to listen for clients to connect. Then I created a tun device. ...
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84 views

configure allowed_tcp_congestion_control via config files in linux kernel

I am trying to come up with a custom set of TCP congestion control variants as part of the tcp_allowed_congestion_control. I do have multiple variants on my tcp_available_congestion_control list but ...
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59 views

Can we Bring Up eth1 after removing e1000e modules?

I am trying to setup TCP in RTnet. I am not sure whether its possible. I read that RTnet is not supporting TCP. Is that so? So now I am trying to setup rteth0 as server and eth1 as client. To setup ...
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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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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. ...
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11 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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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 ...
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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: ...
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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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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 ...
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8 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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105 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 ...
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54 views

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 ...
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73 views

Too many “ESTABLISHED” connection

I have a setup where my client talks to the server via CORBA connection. Both client and server runs on different machines. When I start my client a connection is "ESTABLISHED" with the server. Once ...
0
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0answers
86 views

Optimizing kernel TCP stack / parameters for services running on one host and communicating over TCP

I have a dual server {} block setup for my webapp running on nginx. For learning purposes I want to play around with performance tuning: Questions: What happens to a request going from one server ...
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247 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 ...
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90 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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203 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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428 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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181 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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136 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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109 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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164 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 ...
0
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90 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?
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210 views

How to make Network alive but speed low, slow for upload, download?

I have own application written (Python, Java) which does upload/download for streaming. Now in my local office network and home network setup i can't simulate slow/low latency network (as a result i ...
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0answers
247 views

No ports can be found using port scan

Problem: I have a laptop and a server (Home-Server) with fc17. They are both using the desktop environment. I am trying to set up a VNC server on Home-Server so that I can set everything up without ...