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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Increasing bandwidth with multiple NICs

If I have two NICs in my system and both are connected to different ISP with different IP addresses, can I distribute my network traffic on them to increase my Bandwidth. I have already looked at ...
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apache webserver unresponsive with server-status showing all child processes waiting for connection

My setup: i have 3 nearly identical webserver machines serving the same high loaded dynamic website with simple load balancing over dns. The service has been working for over two years with the same ...
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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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674 views

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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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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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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Is ECN (Explicit Congestion Notification) turned on by default on Windows Server 2012?

In a company network I noticed that all examined Windows Server 2012 machines had ECN turned on: > netsh interface tcp show global TCP Global Parameters ...
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Block all incoming DNS requests EXCEPT from IPs x,y,

I want to block all incoming requests on my two DNS servers APART FROM certain IP addresses e.g. IP of 1.2.3.4 will be allowed to make requests but NOBODY else will. How do you do this with iptables? ...
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SYN cookies on internal machines

Our system uses Cassandra running on Ubuntu 10.04 and during last spike in traffic we observed the following message in logs: possible SYN flooding on port 9160. Sending cookies. These machines are ...
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Allow X Client Display through TCP on Lucid

On Karmic, to allow other PCs to open and X-Window on a station, one had to edit /etc/gdm.conf and change DisallowTCP to false. That file no longer exists on Lucid. I tried changing an entry in ...
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TCP/IP routing: accessing a LAN device with wrong static IP configuration

I forgot to change the static IP of a network device before moving it from my datacenter network to my home LAN. Since it isn't configured properly for my LAN network, I'm not sure how to access it. ...
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How to change receive queue length of a network interface in Linux?

I have a server running Linux (kernel 2.6.18) which is dropping incoming network packets drastically. I thought it is suffering from this because the length of the receive queue of that interface is ...
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Improving TCP performance over a gigabit network lots of connections and high traffic for storage and streaming services

I have two servers, Both servers hardware Specification are Processor : Dual Processor RAM : over 128 G.B Hard disk : SSD Hard disk Outging Traffic bandwidth : 3 Gbps network cards speed : 10 Gbps ...
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FreeBSD Listen Queue Overflows - can't increase max queue size

I have a decently high trafficked FreeBSD Nginx server, and I'm starting to get a large number of listen queue overflows: [root@svr ~]# netstat -sp tcp | fgrep listen 80361931 listen queue overflows ...
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Why Packet Loss AFTER tcpdump has logged the packet?

We encounter some strange packet loss and want to know the reason for this. We have an imageserver and a server for stressing the imageserver. Both are located in the same datacenter First we run a ...
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1answer
409 views

TCP packet filter based on TCP sequence

I need to build a test environment with a very precise packet loss based on specific TCP sequence or, optionally, on payload content. I couldn't figure out how to do it with tc or iptables. What tool ...
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How to achieve multiple NFS/TCP connections to the same server?

I'm trying to maximize the NFS/TCP bandwidth between a Linux client and a single NFS server over a 10Gbps link. Although each NFS mount has its own device (major/minor), everything comes down to a ...
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240 views

How to fine tune TCP performance on Linux with a 10Gb fiber connection

We have 2 Red Hat servers that are dedicated for customer speedtest. They both use 10Gb fiber connections and sit on 10Gb links. All network gear in between these servers fully support 10Gb/s. Using ...
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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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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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FTP client/server failing on switching to PASV mode

Update The ISP said that they recently added the area where this computer is located to their IPv6 network. Coincidentally, ever since the day they added that area to their IPv6 network, no FTP ...
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1answer
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Does a growing number of TIME_WAIT connections affect server performance?

I have 2 servers, both running RHEL 6, one for Apache 2.2 and one for memcached (memcached-1.4.4-3). I noticed an increase in the number of TIME_WAIT connections on the Apache server netstat -n | ...
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Rotating outgoing IPs using iptables

I am trying to rotate outgoing IPs using iptables. I want to rotate outgoing connections between three IPs, one by one. Here is what I'm doing with iptables: root@server:~# iptables -t nat -I ...
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Why is iptables not dropping packets?

I have the following rule in our iptables config file /etc/sysconfig/iptables -A INPUT -s 84.23.99.97 -j DROP And when I do iptables --list I get the following Chain INPUT (policy ACCEPT) target ...
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1answer
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option http-server-close on HAProxy haproxy-1.5-dev19 will result in Connection: close header sent in response

I basically have the following issue: whenever I add option http-server-close to the haproxy config (either in frontend or backend section), haproxy will send a Connection: close header in the ...
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Server 2012: SYN, no ACKs, on TCP ports higher than 6000

Seems ridiculous to read it back out loud, but I'm at a loss here. Server 2012 Standard. Runs a daemon for an accounting package on TCP 12502; at some point, the server stopped accepting connections ...
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Ubuntu 14.04 TCP established hash table entries

A bit of background I am running two servers under high traffic one with ubuntu 12.04 (linux 3.2.0-69-generic) and one with ubuntu 14.04 (linux 3.13.0-52-generic). I am now trying to secure both. ...
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Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP ...
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Is it possible to run 2 concurrent tcpdump with different options?

I need to run 2 concurrent tcpdump commands with different arguments/options. Why ? Because we wrote some long long scripts compatible with following options : tcpdump -ixenbr0 -s 400 -n -A 'port sip ...
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Rsyslog not logging from remote server

I am trying to set up a centralized log server. I have central server (A) receiving logs via a remote server (B) on port 514. I know it is receiving these. Here are a few entries from a tcpdump on ...
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436 views

Is tcp_keepalive application dependant on Linux?

According to http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/index.html , the kernel keepalive function occurs at the OS level, and doesn't require an application to explicitly call it. However I also read ...
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Is the TCP checksum over the payload?

I was somehow convinced that the TCP checksum was a header checksum (similar to the IP checksum), but I'm now having doubts reading the Wikipedia article: The checksum field is the 16 bit one's ...
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SMTP server force outbound traffic

I'm having some trouble with setting up a SMTP server on a windows server 2003 machine, while trying to send emails using PHP through the internet, but to domain email addresses. Common info: ...
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How can I tell when a TCP connection was created on Linux?

How can I figure out at what time a given (as in currently-open) TCP connection was created?
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Please recommend an affordable cisco product capable of handling up to 100,000 plus simultaneous tcp connections [closed]

I am setting up my server lab, can you please recommend an affordable and very reliable router than can handle over 100,000 simultaneous open tcp connections without breaking a sweat? Thanks!
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Configuring keepalives with TOAD client communication

I have a scenario where long-idle sessions of TOADSoft client communication with the Oracle server seem to be torn down as they timeout on an intermediate state-full firewall. These sessions could ...
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What happens when connecting to port in TIME_WAIT state?

I'm trying to understand the effect of TIME_WAIT on subsequent TCP connections. I understand how TIME_WAIT behaves when net.ipv4.tcp_tw_reuse = 1, as explained by this answer. But what happens when ...
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REDSOCKS goes 'out of file descriptors' when trying to redirect all outgoing (TCP) traffic from my Linux machine

I'm trying to redirect all outgoing TCP traffic from my linux box to the remote SOCKS5 proxy server. Currently I'm using the following rule in the OUTPUT chain: sudo iptables -t nat -A OUTPUT -p tcp ...
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windows firewall , some ports not listening

I've added an inbound connection rule for my windows 8 firewall on windows server 2012: I've restarted the Windows Firewall. When I check that port using this program, it says that it is not ...
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Is an Apache use TCP port on each connection?

Our system admin said "Apache use a TCP port on each connection" so A server can serve 65534 (MAX) simultaneously. is it Right? I think Apache use only 80 or 443. But , he use many file descriptor ...