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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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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1answer
800 views

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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776 views

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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4answers
1k views

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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2answers
8k views

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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5answers
322 views

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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2answers
5k views

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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2answers
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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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1answer
936 views

HTTP, TCP, UDP and connectionless

I am a bit confused with HTTP lately. Some facts are that TCP can operate connection orientated or connectionless, this I understand. TCP though is connection-oriented while UDP is connectionless ...
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5answers
598 views

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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6answers
821 views

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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2answers
2k views

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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1answer
4k views

Unexpectedly shrunk window

I run a major media upload/download site and I noticed these: Is this serious or background noise due to the big file sizes and is there any tweaks I can add to /etc/sysctl.conf to improve and ...
4
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1answer
394 views

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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3answers
8k views

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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2answers
6k views

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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2answers
5k views

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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3answers
3k views

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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1answer
172 views

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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5answers
7k views

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 ...
4
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1answer
747 views

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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2answers
7k views

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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2answers
166 views

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 ...
4
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1answer
913 views

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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2answers
530 views

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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1answer
470 views

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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3answers
2k views

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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2answers
266 views

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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2answers
2k views

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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4answers
1k views

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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2answers
1k views

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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2answers
311 views

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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1answer
3k views

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 ...
4
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2answers
3k views

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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3answers
2k views

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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1answer
1k views

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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3answers
364 views

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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1answer
4k views

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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2answers
169 views

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 ...
4
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1answer
285 views

HaProxy for game servers, what's wrong with my configuration?

I host a website with a game client that uses TCP for connections. I am currently looking for a way to proxy my connections from one server to my origin server. I have tested Iptables forwarding and I ...
4
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1answer
550 views

Page allocation failures on iSCSI storage

We have a CentOS 6.3 iscsi server (16GB RAM) running on Infiniband bus (ipoib). When the load is high I can see multiple errors: Sep 3 23:22:20 stor4 kernel: tgtd: page allocation failure. ...
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3answers
538 views

How do I diagnose network corruption on an Internet path?

I run a few hosts on network A that make requests to servers (which I don't own) on network B, somewhere across the Internet. Unfortunately, many of these requests get corrupted. If I make the ...
4
votes
1answer
528 views

Behaviour of solaris tcp stack with relatively high RTT and bursty traffic

I have an application that is distributing data from New York to Tokyo over TCP running Solaris 10. Mean throughput is < 1Mbps, peak throughput can reach 20-30Mbps for seconds at a time though ...
4
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1answer
2k views

low latency TCP settings on windows 2008 R2

I am running a third party software on a W2008 server. This client connects to a server via TCP. The average ping times between the two are 1ms. However, when I check the tcp connection in resource ...
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1answer
618 views

Meaning of tcp_delack_min

the current Linux Kernel (e.g. 2.6.36) uses Delayed Acknowledgments (delack). In /include/net/tcp.h it says: define TCP_DELACK_MIN ((unsigned)(HZ/25)) So, for a Kernel using a HZ value of ...
4
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1answer
620 views

tcpdump and congestion window

Sniffing http traffic to my (linux) server it seems like it always responds advertising a window size of 14. It isn't affected if I change the default initcwnd size (with ip route), and it doesn't ...
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2answers
2k views

Remote server hangs, gets stuck. How to debug?

I have an vps running on VmWare ESX with Ubuntu 8.04 LTS. It has been running smoothly for the past 3 months, however recently we've notices two strange bugs. a. The server hangs, today was second ...
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1answer
3k views

TCP/IP & throughput between FreeNAS (BSD) server & other LAN machines

I have got a question for someone that knows BSD a bit better than me that are in regards to my LAN setup at home/work here outside Chicago. I can't seem to fully optimize my network's (LAN) ...
4
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1answer
133 views

Change TCP wait for ACK timeouts in Win7/WinServer

Is there any possibility to change default wait for ACK timeout in TCP network on Windows 7 or Windows Server ? I'm using very slow network ( 1200 bps ) and want to tweak TCP. When using default ...
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3answers
3k views

How to configure a redhat/centos/amazon linux server for 1million open tcp connections?

I've been reading the following article: http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-1 More than 65536 TCP connections on Linux And wondering if there's ...