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Questions tagged [tcp]

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.

TCP is just one communications protocol on the web. Others include:

  • User Datagram Protocol (UDP)
  • Internet Control Message Protocol (ICMP)
  • Hypertext Transfer Protocol (HTTP)
  • Post Office Protocol (POP3)
  • File Transfer Protocol (FTP)
  • Internet Message Access Protocol (IMAP)

TCP on Wikipedia

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What does LAST_ACK mean, as a State value in netstat?

If a Windows server has several thousand ports open in LAST_ACK state (as shown by netstat), what could this mean? Is it because one endpoint is waiting for the other to respond?
Nick Bolton
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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? netstat -ctp did not help, the connections were too…
pmezard
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How to check TCP timeout in linux / macos?

I have a network problem on my MacOS that i need to troubleshoot. I know that TCP socket has internal timeout that will close connection if remote party is not responding (but no graceful disconnect either). Is it any command/tool i can use to check…
grigoryvp
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Under HTTP2, how often are new TCP connections initiated?

I understand that HTTP2 aims to keep everything under a single TCP connection, and I was wondering how often TCP connections would be torn down. For example, if I visit youtube, do some browsing, leave the site, and come back, will I be re-using the…
fruglemonkey
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Why are connections in FIN_WAIT2 state not closed by the Linux kernel?

I have an issue in a long-lived process called kube-proxy being part of Kubernetes. The problem is that from time to time a connection is left in FIN_WAIT2 state. $ sudo netstat -tpn | grep FIN_WAIT2 tcp6 0 0 10.244.0.1:33132 …
Adam Romanek
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What is the best way to measure latency via a "telnet to port" test, preferably with built-in Linux tools?

I'm writing a Graphite/Diamond collector measuring network latency. Specifically it should measure the time it takes to open up a connection to a port on a remote server. And it needs to work via script, i.e. no humans on the keyboard running this…
r3cgm
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Determining at what time a currently open TCP connection was created?

How can I find out at what time a currently open TCP connection was established on Linux?
opsguy
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How can I tune the initial TCP retransmit timeout?

The initial TCP RTO value of 3s is too long for most LAN-based applications. How can I tune it lower? Is there a sysctl?
claymation
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How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket pair that had its close() initiated on the server…
Pawel Veselov
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Is my TCP connections sabotaged by my country's government?

I am suspicious that my country's government is destroying the received ACK packet on TCP connections, somehow. When I try to establish a TCP connection to an outside host on ports other than 80 the TCP handshake will not be successful. I captured…
Mohammad
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What am I misunderstanding about calculating MTU?

Okay, I just finished resolving a jumbo frames issue between a few Xserves, a Netgear GSM7224, and a Drobo B800i. It turned out that the Xserves (Mac OS X 10.6.8 Server) and the Drobo B800i accept the MTU in bytes as normally expected (1500-9000),…
morgant
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Netcat fails to start in listening mode

I'm using CentOS 6.7 (Final) system, and when I try to run nc in listening mode it prints the following: nc -l 1234 nc: Protocol not available The port is not bound. I tried other port numbers too. This bug seem to have been reported already:…
Ilya I
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SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- | | ---o--- 172.16.11.5 …
nyzsirt
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Why is my web server dropping connections with a TCP reset at high load?

I have a small VPS setup with nginx. I want to squeeze as much performance as possible out of it, so I've been experimenting with optimization and load testing. I'm using Blitz.io to do load testing by GETing a small static text file, and running…
Erik Swan
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NAT Gateway - Maximum connection limit

I know just enough networking to be dangerous. The nitty gritty low level details of NAT are not something I am particularly knowledgeable about. I accidentally found myself in a discussion earlier today about placing a bunch of our nodes behind a…
Daniel Widrick
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