TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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How do I optimize TCP stack for HTTP server?

I have a HTTP server that serves only two kinds of page: about 10 KB and about 16 KB (both compressed, other files are from CDN). As the latency is quite high (ping takes more than 300 ms), I want to ...
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Finding short-lived TCP connections owner process

Running tcpdump on local connections to an apache server, I found TCP connections being established and closed immediately every 2 seconds. How do I find which process is responsible for these? ...
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What is the meaning of “Treason Uncloaked” in Linux?

On a Linux Apache server, from time to time, there are messages saying TCP: Treason uncloaked!. There are previous questions on ServerFault explaining the fixes for this issue. However does anyone ...
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Is SYN flooding still a threat?

Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python ...
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Netstat -s showing (and growing) “packets pruned from receive queue” and “packets collapsed in receive queue”

we are seeing the following: [root@primary data]# netstat -s | grep buffer ; sleep 10 ; netstat -s | grep buffer 20560 packets pruned from receive queue because of socket buffer overrun ...
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better TCP performance over a “high delay network”

I’m trying to improve my TCP throughput over a “high delay network” between Linux machines. I set tcp_mem, tcp_wmem and tcp_rmem to “8192 7061504 7061504”. I set rmem_max, wmem_max, rmem_default and ...
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How to increase maximum connection backlog limit in windows 2008 server

I have a Windows 2008 Server. Its maximum connection backlog limit (TCP) is 200. Is there any way to increase this limit to a higher value – say 1000 or 2000? In this article you will find ...
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Network error with 65k of TIME_WAIT connections

We had some trouble with one of our image servers last week and need some help. See our munin monitoring graph: We are runing debian squeeze and we have lots of requests because this is one of our ...
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Too many TCP connections causes disconnections

I have a game server which runs with TCP connections. Server disconnects users randomly. I think its related with TCP settings of server. In local development environment written code can handle ...
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Forwarding linux terminal from serial port to TCP with socat

I'm working on embedded ARM platform, Slackware. I'm using G24 Java modem which is configured to forward data between ports /dev/ttyS1 and /dev/ttyACM0, so anything that goes onto any of these ports ...
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POST of MTU + ~798 bytes gets lost

I have a very weird issue with certain packets not arriving on the destination host. It happens when we transmit a POST that is somewhat larger than the MTU. We can reproduce it with this script: ...
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Where are my TIME_WAITs on Mac OS X?

No TIME_WAITs on Mac OS X Normally, when a TCP connection is closed, the socket on the side where close() is called first is left in the TIME_WAIT state. When one of the peers is a Mac OS X (Lion) ...
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Effect of distance from server on page load speed

I measured the load speed of a static image file severed by nginx from my server (using pingdom service). The server should normally process this request within few seconds. My server is located in ...
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Is there a way to see what is actually filtering TCP port communication?

nmap -p 7000-7020 10.1.1.1 Will output all the filtered ports Starting Nmap 6.40 ( http://nmap.org ) at 2015-03-04 12:18 EET Nmap scan report for 10.1.1.1 Host is up (0.00091s latency). PORT ...
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Should I use TCP or UDP to run a web server

I have just installed Apache web server on my computer. I have managed to use it locally (I can open index.php from my computer using my web browser). But I would like to make my web site available ...
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Which ports to use on a self-written tcp server

I am about to write tcp-server for a project my company is working on. The server will use several port for different tasks. During development we use just some portnumber we like: 1400, 1500, ...
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TCP sequence number

I would like to know if two segments of same sequence number arrive at the destination, which segment will get accepted ? For eg: A clients sends a packet to a server and wait for an ...
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Reduce firewall rules by half - one iptables rule for tcp and udp

I have a number of iptables rules on my firewall that look like this: iptables -A zone_lan_forward -p tcp -d 1.2.3.0/24 -j ACCEPT iptables -A zone_lan_forward -p udp -d 1.2.3.0/24 -j ACCEPT Is ...
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What are the ramifications of setting tcp_tw_recycle/reuse to 1?

I set both tcp_tw_recycle/reuse to 1 in my configuration file. What are the ramifications of doing this? If a tcp socket is re-used, does that pose a security risk? i.e. 2 different connections both ...
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Share one IP address with a simple router

We have just moved into a new office and have been given our 'internet connection' in the following form: One Ethernet cable in the corner of the room An IP address with subnet mask 255.255.255.0 ...
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What causes a delay of 100 ms in initiating an HTTP connection?

Settings: this is a quad CPU machine, plenty strong, not loaded at all (neither CPU nor network), the client is a Windows Server 2008 64bit, the server is a linux box. I have four threads that are ...
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VMXNET3 performance on Linux on ESX 5.0

What kind of performance can I expect from VMXNET3 adapter when running two Linux guests on the same VMware ESX private network defined between those guests? I use VMXNET3 adapter for communicating ...
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What happens to tcp packets when they are unable to finish the 3 way handshake?

Firewall for a virtual dedicated server. I was looking into how to prevent a FIN scan and it got me thinking about the consequences. A lot of people are using this rule: -p tcp --tcp-flags ...
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Karmic Koala (Ubuntu): enable remote x clients through TCP

It seems every version of Ubuntu has a different way to enable remote connections to the local X server. I'm asking this question, while I do my own research: how can I enable the X server listening ...
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Speed up rsync by running multiple instances at once?

I have to transfer a big directory to another server. My problem is that i cannot use the full bandwidth that would be available, because one concurrent tcp stream does not get as fast. Basically ...
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lots of packets pruned and packets collapsed because of socket buffer low/overrun

i've set up a test machine (debian squeeze 2.6.32 on a linode 2048 machine) that interact with an api that returns large chunks of json. It calls the API 3000/minutes asynchronously, the api is ...
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Can a TIME_WAIT connection be restored?

Is it possible to restore a connection that is in state TIME_WAIT? If not, I use raw packets (forgering the source), is it possible? (Please understand that I do not intend to do bad things, it's ...
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What does tcp_orphan_retries set to 0 mean?

Does setting tcp_orphan_retries to 0 mean there is no limit to retries, or does it mean that it won't retry at all?
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How to “silence” a TCP connection in one direction?

I have 2 applications that communicate through TCP. They keep their connection through a heartbeat of 30 seconds. I need to simulate a scenario where one side fails to send this heartbeat to test the ...
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Exhausting Linux machine TCP socket limit (~70k)?

I am the founder of torservers.net, a non-profit that runs Tor exit nodes. We have a number of machines on Gbit connectivity and multiple IPs, and we seem to be hitting a limit of open TCP sockets ...
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Server not sending a SYN/ACK packet in response to a SYN packet

Using iptraf, tcpdump and wireshark I can see a SYN packet coming in but only the ACK FLAG is set in reply packet. I'm running Debian 5 with kernel 2.6.36 I've turned off window_scaling and ...
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tcpdump output with iptables REJECT policy enabled

Quick question. I have a firewall with these simple rules: iptables -A INPUT -p tcp -s 127.0.0.1/32 --dport 6000 -j ACCEPT iptables -A INPUT -p tcp -s 192.168.16.20/32 --dport 6000 -j ACCEPT ...
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Why does the TCP Chimney Offload feature on some ethernet cards fail to pass some network packets to the OS?

In http://support.microsoft.com/kb/942861 Microsoft reports that in some situations Microsoft SQL Server experiences network issues due to the network card having a TCP Chimney Offload turned on. I ...
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(Why) does FreeBSD 'net.inet.tcp.always_keepalive' violate RFC1122?

While working on a server application that runs on FreeBSD and uses TCP, I noticed that TCP keepalive probes get sent even though my application explicitly disables SO_KEEPALIVE on TCP sockets. ...
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What characteristic of networking/TCP causes linear relation between TCP activity and latency?

The core of this problem is that our application uses websockets for real-time interfaces. We are testing our app in a new environment but strangely we're noticing an increasing delay in TCP websocket ...
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Increasing tcp slow start Initial Window in linux 3.0 kernel

I was checking the IW for my site and realized that its 4. [user~]$ sudo tcpdump -n -i any 'tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn and port 80' tcpdump: verbose output suppressed, use -v or ...
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Packet loss during TCP handshake

I have to implement a pseudo TCP handshake that leads into a file transfer. I have no problem doing the file transfer: simple send-acknowledge. What I can't wrap my head around is how to do the three ...
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Collect per-TCP connection statistics on Linux without promiscuous mode (e.g. without tcpdump)

Linux keeps per-interface statistics, ifconfig reports them just fine. But does Linux keep per-TCP connection statistics, specifically, how many rx/tx bytes this session? If it does, I sure can't ...
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All connections from this network get stuck in SYN_RECV state, connections from my home or phone properly get ESTABLISHED

My server (a linode VPS) suddenly started to timeout on every request yesterday. I'm pretty inexperienced in networking and would love to learn a process for debugging these connectivity issues. ...
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How to enable TCP for DNS resolution?

I've been doing some reading about this, according to what I understood this is possible, but HOW??, I know UDP is much much better for DNS resolution but because of so many issues an restrictions, ...
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Load Balancing long running TCP connections

I'm trying to research the best way to load balance long running TCP connections for the following scenario: We have multiple servers behind a redundant set of firewalls and clients establish long ...
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Should I limit end-user gigabit ports to avoid saturating uplink/trunk connections?

We have a campus with 16 buildings and older 850nm 1Gbps fiber links between the buildings, that all come to a core switch for our servers that also uses 1Gbps ports. We're finally starting to replace ...
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syn/ack sequence number confusion

I was looking at some random traffic in wireshark and came across this (using relative seq/ack numbers): 1. myIP -> 74.125.227.96 [SYN] seq=0 2. 74.125.227.96 -> myIP ...
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High Instances of Zero Window Messages

On my web servers I am seeing a high rate (106 over ~13 seconds or 300,000 packets) of zero window update messages sent form my web servers to my database servers during peak traffic. Firmware is ...
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10k-20k TCP connections on windows server(s)

What kind of configuration do I need for a Windows based server(s) to support 10K-20K TCP connections simultaneously. 99% of these connection will only send keep alive (but will remain active) signals ...
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Different versions of iperf for windows give totally different results

Measuring TCP output from a Windows client to Solaris server: WXP SP3 with iperf 1.7.0 --> returns an average around 90Mbit Same client, same server but iperf 2.0.5 for windows --> returns an average ...
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IPtables rate-limit, What are the differences between modules? Recent, Limit

I am doing some rate-limiting with IPtables, and i'm not sure if I should use "Recent" or "Limit" What are the differences between the two? If they both achieve the same result, which one has ...
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iptables redirect IP address

I have an application (mirth) on a server (10.2.2.200) that on port 6661 is receiving an HL7 feed from an egate server from 10.0.1.234 port 56789. For each message it receives/processes, its ...
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What is the best TCP congest algorithm to use for a mobile device?

Given the multitude of TCP algorithms available now and the rise of Linux based mobile devices, what are ideal algorithm(s) to consider? From reading of the various implementations, Veno and ...
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Optimizing OS for HTTP requests

We make a lot of HTTP requests. Recently, we've started thinking about optimizations at the OS level to make more requests from a single machine. In order to check the performance of our OS, I've ...