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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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Do DNS queries always travel over UDP?

I've spent a bit of time researching this topic and can't seem to find an exact answer, so I'm fairly confident it's not a duplicate, and while my question is based on a security need, I think it's still safe to ask here but let me know if I need to…
Caderade
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Random TCP RST's on certain websites, what's going on?

Short version: One Windows Server 2012 machine on my network is getting persistent but intermittent TCP RSTs when connecting to certain websites. Dunno where they're coming from. Check out the wireshark log for my analysis & questions. Long…
Morty
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"Possible SYN flooding" in log despite low number of SYN_RECV connections

Recently we had an apache server which was responding very slowly due to SYN flooding. The workaround for this was to enable tcp_syncookies (net.ipv4.tcp_syncookies=1 in /etc/sysctl.conf). I posted a question about this here if you want more…
Alex Forbes
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How to troubleshoot connectivity when curl gets an *empty response*

I want to know how to proceed in troubleshooting why a curl request to a webserver doesn't work. I'm not looking for help that would be dependent upon my environment, I just want to know how to collect information about exactly what part of the…
chad
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Under what circumstances is TCP-over-TCP performing significantly worse than TCP alone (2014)?

Many admins keep perpetuating - on ServerFault and elsewhere - how bad of an idea TCP-over-TCP is, e.g. in VPNs. That even the slightest packet loss will make one suffer from at least severe throughput degradation if not TCP meltdown, and that…
Nils Toedtmann
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traceroute TCP equivalent for Windows

I'm trying to determine where connectivity to an external host using a specific TCP port is being blocked. Traceroute for Windows only uses ICMP, and telnet will only tell me that the port is blocked and not where. Does anyone know of a Windows…
Lloyd Mangram
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Tuning iSCSI storage

This is a Canonical Question about iSCSI we can use as a reference. iSCSI is a protocol that puts SCSI commands as payload into TCP network packets. As such, it is subject to a different set of problems than, say, Fibre Channel. For example, if a…
Basil
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Finding cause of TCP retransmission within a LAN

Hello denizens of Server Fault I have an irritating problem with a LAN of about 100 computers, 2 Windows domain servers, and 12 VoIP phones. Since their installation around a year ago, every week or so, we notice a VoIP phone resetting itself -…
Surreal
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What is the "in-the-wire" size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP headers, which are 28 bytes (20 IP + 8 UDP). That…
chrisapotek
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How do I prevent TCP connection freezes over an OpenVPN network?

New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast packets, which doesn't seem to be possible with tun…
Jason R
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Sockets found by lsof but not by netstat

I have an application which is running out of file descriptors, apparently by opening sockets, but I can't find out exactly what these sockets do. These appear in the lsof output as java 9689 appuser 1010u sock 0,5 263746675 can't…
Robert Munteanu
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I'm designing a system to handle 10000 TCP connections per second, what problems will I run into?

I have a relatively new 8-core box running CentOS. I would like to develop a stats server that uses TCP. It's very simple, it accepts a TCP connection, increments a counter and closes the connection. The catch is it needs to do this at at least 10k…
Larry G
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What does "net_ratelimit: 44 callbacks suppressed" mean on a linux?

I'm trying to tune Snort performance on a Debian based router. I was seeing stuff like: snort packet recv contents failure: No buffer space available So I upped the buffers to 8M and when that didn't work I tried 16M, per the tuning guide at…
Antonius Bloch
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What is the best way to transfer a single large file over a high-speed, high-latency WAN link?

This looks related to this one, but it's somewhat different. There is this WAN link between two company sites, and we need to transfer a single very large file (Oracle dump, ~160 GB). We've got full 100 Mbps bandwidth (tested), but looks like a…
Massimo
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What is [PSH, ACK] doing during my connection to a global catalog server?

A linux server of mine is trying to establish a LDAPS connection to a global catalog server and the connection is getting dropped (presumably by the GC side). For the purpose of discussion, let's say that 1.1.1.1 is the Linux server and 1.2.3.4 is…
Mike B
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