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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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Difference between net.core.rmem_max and net.ipv4.tcp_rmem

What's the difference between net.core.rmem_max and the third value of net.ipv4.tcp_rmem? Which has the higher priority for tcp connections? For below two examples, what's the max buffer for tcp connections? Case 1: sysctl -w…
bydsky
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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 there a shortcut for having two rules - one for tcp and…
Big McLargeHuge
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Understanding Ports: How do multiple browser tabs communicate at the same time?

I realized today that I fundamentally don't understand how port communication works. If I fire up an instance of a webserver listening on port 80, it can respond to many requests from many different browser tabs, all communicating over port…
Marty Pitt
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Slow Transfers over Distance

From our NY Datacenter, transfers to locations that are farther away are having poor performance. Using speed test to test various locations, we can saturate our 100 mbit uplink to Boston and Philadelphia easily. When I use speed test to location…
Kyle Brandt
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tool for splitting pcap files by TCP connection?

Is there tool to split a packet capture file (in pcap format) into separate files for each TCP connection ? (other than a home grown shell script which probably needs to run twice over the capture...). Something like wireshark's 'follow TCP stream'…
Andre Holzner
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What causes duplicate ACK records?

We're reviewing Wireshark captures from a few client machines that are showing multiple duplicate ACK records which then triggers retransmit and out-of-sequence packets. These are shown in the following screen shot. .26 is client and .252 is…
Sam
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dump tcp connections without tcpdump

On a centos box, I like to dump tcp connections - I would like to see if a server tries to send requests to a certain IP. Usually tcpdump would do the trick - but tcpdump is not installed, and installing software is not an option (because of company…
Isaac
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How to expose a UNIX domain socket directly over TCP

I'd like to have a UNIX domain socket, say /var/program/program.cmd for example, exposed via TCP, lets say on port 12345. I'd also like this to be running full time in the background. What's the best way to do this? If its relevant the system is…
SimonJGreen
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Apache Tomcat chokes after 300 connections

We have an apache webserver in front of Tomcat hosted on EC2, instance type is extra large with 34GB memory. Our application deals with lot of external webservices and we have a very lousy external webservice which takes almost 300 seconds to…
john titus
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Troubleshooting Network Speeds -- The Age Old Inquiry

I'm looking for help with what I'm sure is an age old question. I've found myself in a situation of yearning to understand network throughput more clearly, but I can't seem to find information that makes it "click" We have a few servers distributed…
Univ426
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How can I search the info column in Wireshark?

Wireshark | Windows I want to search a packet capture of SMTP traffic for specific addresses/messages. Normally, I just sort the info column and browse but it would be nice if I could just run a search or filter for the specific string I'm looking…
Mike B
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Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is this necessary? Surely the error correcting…
Aditya K
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How does Intel AMT (Active Management Technology) not interfere with the TCP/IP host stack?

The Intel dev kit I've been using includes a remote management feature (also see the Ubuntu man page here) which allows remote reboots in case the operating system hangs. It has the capability of listening a handful of ports (16992 and 16993, to be…
mpontillo
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Why do some connections time out and others get refused?

I have noticed that sometimes while trying to telnet in some random port, I have observed two kind of scenarios: $ telnet example.com 3432 Trying 173.252.110.27... $ telnet example.com 3432 Connection Refused. Can someone explain me what is…
pradeepchhetri
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Proxy with netcat forever

I am proxying a VNC TCP server port with netcat. The proxy machine runs linux. This is the comand I use: mkfifo backpipe nc -l 5902 0backpipe 10.1.1.116 is the "remote" machine with the original VNC service running…
Alojz Janez
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