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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TCP congestion control

I was curious to know which are the default TCP congestion control method used in latest version of MacOSx, linux kernal, windows 8, windows 7 and windows xp. Does it use newreno or anything newer?
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DrayTek Vigor 2830 open port issue

We're using a Vigor2830 for routing VoIP/SIP traffic. One of the ports required to be open is 5090 for TCP/UDP. Going into the open ports section of the Vigor menu we have opened all the ports ...
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7 views

Reason for TCP Slow Start in Subsequent Connections

From my understanding TCP slow start is used to compensate and prevent congestion and loss. When a connection is successfully established and used for a while, the bandwidth of the TCP connection is ...
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pfSense does not close connections coming from LAN

I created a NAT rule that redirects external_ip:1234 of modem (pfSense itself) to 192.168.1.100:1234. I also wrote a server application which listens for connections on 192.168.1.100:1234. When I ...
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19 views

Socat not closing tcp connection

I use socat 1.7.3.1-r0 and run following command on an alpine 3.3 linux server: socat -d -d -d PTY,link=/dev/ttyFOOBAR,echo=0,raw,unlink-close=0 TCP-LISTEN:7000,forever,reuseaddr Socat will listen ...
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11 views

Connecting from WAN to LAN

I'm developing an app for my family that uses sockets to comunicate between devices in LAN or WAN. As IP addresses change constantly I am planning an FTP server for address book and TCP/IP for ...
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2answers
18 views

TCP: Disable pure ACKs?

I have a scenario where I wish to disable pure ACKs (TCP ACKs with no data), but I can't find how to do this. Is there an option that I can set so that ACKs are always piggybacked onto the next data ...
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30 views

ping works but iperf3 doesn't show any traffic for TCP

machine A has IP (eth0: 192.168.1.1, eth1: 10.10.xxx.yy) machine B has IP (eth0: 192.168.1.2) A and B are connected through RJ5 on eth0, both sides. ping works fine on both side, but when running ...
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58 views

Why game latency fluctuates aggressively during day?

I play World of Warcraft (uses TCP) from India, on a server located in France. I get 180-200ms in-game past midnight which is quite comfortable for me, and unfortunately the best I can get due to the ...
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21 views

How to add latency to TCP packets?

I have tried netem and wanem neither seem to be affecting the TCP packets. How can I add latency to TCP packets?
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34 views

RST sequence number and window size

RFC793 states the following about RST processing: In all states except SYN-SENT, all reset (RST) segments are validated by checking their SEQ-fields. A reset is valid if its sequence number is ...
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25 views

Can two different applications bind the same port on a host if they use different protocols?

 my question is quite clear I think. If two applications use different transport layer protocols (e.g. TCP and UDP or something else) can they open the same port number? How does the OS do the ...
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tcp sesssion duplicate acknowledgement and retransmission

Please help in understanding why the receiver keeps sending duplicate acknowledgement yet the senders keeps sending old packet sequence (re transmitting of old packet seq)
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22 views

Duplicate and retransmission

Please help me understand why the receiver keeps sending duplicate acknowledgements, yet the senders keeps sending old packet sequence (re-transmitting of old packet seq) in the below capture: Please ...
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1answer
17 views

A bunch of tcp unseen segments and duplicates on wireshark?

Recently, my Mac has been unable to use the internet well. Even though it said my ping was between the ranges of 10-20 ms and my download speed was around 20 Mbps along with around a 10 Mbps upload ...
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1answer
32 views

TCP RST Connection - Netflix - Only on Linux

I wouldn't have asked this here, but I am at wit's end, this makes absolutely no sense at this point. I have been trying everything. I have a single iptables rule: -A POSTROUTING -o eth0 -j ...
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45 views

Drop resilient tcp tunnel

I'm looking for a tcp tunnel that can provide connection drop resilient TCP connections to my VPS. Currently when I have some tool connected to my VPS and I switch from Wifi to LAN or my internet dies ...
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78 views

No connection could be made because the target machine actively refused it

On Windows machine, I start a server on port 62325 $ netsh firewall show state shows: Ports currently open on all network interfaces: Port Protocol Version Program ...
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Is it necessary for an RST packet to have an acknowledgement number?

I am studying about TCP reset attack. I know that some RST packets have an acknowledgement number (with the ACK bit set), and some RST packets do not have an acknowledgement number (the ...
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18 views

Acknowledgement number of an RST packet

This question states that the acknowledgement number of an RST packet should be 0, but I have found it to be other than 0 when I captured some HTTP packets using Wireshark. So when does the ...
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1answer
15 views

Can't get windows host file to forward HTTPS headers

I'm currently trying to write a proxy in C# using the host file to redirect requests (specific request). I only want it to intercept one address. It's on Windows and the proxy is run locally on the ...
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22 views

Still Lost on Blocking TCP Port Connections form Terminal

I'm still not 100% understanding what to do in Terminal to block certain URLs for specific ports. And I don't want to use Little Snitch. I really want to wrap my head around this. So if someone can ...
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2answers
78 views

Send TCP with incorrect checksums

I'm having trouble sending large files to an OpenStack machine. Our Internet connection is over LTE so bad packets are to be expected. However, even sending data over TCP results in corrupted data ...
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2answers
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what distinguished OSI from TCP/IP in practice?

so i am going through cisco ccent/ccna. working through the text on my own just for general useful knowledge. so in the early part of the book it goes into describing the different layers of the ...
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37 views

Close a TCP connection using nmap

I am trying to close connections in command line. For instance, I am trying to close my SSH connection with this Nmap command: $ sudo nmap -p 22 --scanflags RST <mySSHServerPublicIP> $ sudo ...
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18 views

Where do I start to troubleshoot this strange activity from my firewall?

I noticed that my firewall yesterday blocked outgoing attempts starting at port 61494 and worked its way up to 62381, making a TCP outgoing attempt at each port once. The remote IP address seems ...
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TCP and UDP do not work with firewall

I can not connect my TCP-Client to my TCP-Server. Here is my Code: http://stackoverflow.com/questions/35661591/tcp-server-does-not-work-with-firewall I have already opened my TCP-Port "8888" in the ...
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During queuing delay, do TCP, IP, and Data Link headers act as a packet or 3 different packets?

According to the definition from wikipedia, I found processing delay to be the delay caused by router processing the packet header. I am just wondering are TCP, IP, and Data link Headers all ...
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36 views

Why ICMP is different that TCP and UDP? [closed]

what is the difference between Internet Control Messaging Protocol over Transmission Control Protocol and User Datagram Protocol
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48 views

Can HTTP deliver video over the internet or is that TCP?

The post below talks about delivering video content to users via HTTP. Is it confusing it with the TCP protocol? ...
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44 views

How to simulate TCP simultaneous open and close conditions?

I am learning TCP/IP protocol. I want to see simultaneous open, close, half open/close, etc conditions in practice. I have created simple TCP server and client program. How can I simulate simultaneous ...
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36 views

Is there a way to completely disable TCP keepalive?

I'm trying to disable TCP Keepalive in a linux machine. If I set the three keepalive parameters to 0, the machine refuses connections. sysctl net.ipv4.tcp_keepalive_time=0 sysctl ...
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Ubuntu IPTables

I started hosting my game-server on Ubuntu Linux 14.04 I am having an issues ، some enemies/bug abusers log in 2+ characters in the same second then they spam a certain spell/word that lags/stops my ...
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How to know that I passed the firewall from the TCP connections?

In my company, in order to access some intranet-sites, I have first to login to webpage (which I suppose is a firewall or something) with my account. If I login from FF for example, I can access the ...
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NAT doesn't allow TCP ACK for sent TCP SYN

We are using TCP Simultaneous Open for connecting TCP socket. Lets call one SideA and other SideB. From the wireshark log I see that first two SYN sent from SideB is blocked by SideA NAT. Then SideA ...
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41 views

How does a Router/Modem obtain the Port Number from an IP Datagram?

The IP datagram header is a layer below the TCP segment which contains information on the port. Therefore before a firewall can inspect a port number, must the IP datagrams be rebuilt into the TCP ...
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Wireshark FTP multiple ACK?

I'm trying to visualise somes frames that correspond to a file transfer between two machines on Wireshark. The thing is that there are multiple ACK for each FTP-DATA segment and I don't understand ...
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62 views

Replay captured TCP packets

I captured a tcp traffic using wireshark and saved the traffic in pcap file. I did two tests: Test 1: sudo tcprewrite --infile=capturedtraffic.pcap --outfile=temp.pcap ...
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64 views

Connection remains flagged as ESTABLISHED even if host is unconnected

I am working on a Linux embedded distribution and I need to monitor incoming and outcoming connections (if they are still actives etc.) and I am experiencing issues because I noticed that, even if the ...
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41 views

Windows 7 pc opening port 139 from random IP addresses

When I run CurrPorts (a TCP monitoring tool for nirsoft) I get the expected output plus entries that I do not understand. My LAN is 192.168.1.x. My pc is set to a static IP of 192.168.1.12. But I find ...
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40 views

Ways in Which TCP/IP Stack Fails?

In a variety of books and learning materials, we're told that if pinging the localhost/loopback address fails, this is a sign of a malfunctioning TCP/IP stack. What we aren't told is why/how this may ...
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47 views

TCP slowstart by threshold value

I was doing excercises out my book. But there are no answers in the book. This Question is very interesting to me. Does somebody now the answer and why it that answer? A lonely sailor on the Pacific ...
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50 views

Unstable Transmission Rate in TCP by Packet Loss

Is it true that TCP does not provide a stable transmission rate, because TCP always keep increasing the bandwidth until there is a packet loss?
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61 views

TCP on the same (server side) source port to multiple (different destinations)?

Question 2 Is it true that a TCP server may send segments with the same (server side) source port to multiple (different destinations)?
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60 views

Windows 10 dropping TCP connections after 30 seconds

On my Laptop (DELL Latitude E5530) with a completely fresh Windows 10 Enterprise installation any TCP connection gets disconnected after close to exactly 30 seconds. I noticed it first when Skype for ...
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216 views

Relation between TCP conversations and TCP streams in Wireshark

I have read about Conversations and TCP Streams but I'm still a bit unsure how they relate to each other if they are on the same layer. For different layers, it's clear to me that e.g. an IP ...
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1answer
57 views

Connection timed out when connecting to a remote tcp port

I have deployed my application on Linux CentOS. The app connects to a remote TCP port but it throws a connect timed out exception. I tried to connect it via telnet but the port doesn't respond. I am ...
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637 views

How to increase RWIN Value in Windows 10?

We all know that a lot of things have been deprecated and there was also the introduction of auto scaling in earlier windows versions. Right now after using this analyzer ...
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1answer
66 views

TCP connection only working one way on my local network (trying to connect with Synergy)

I am using Synergy to connect my desktop (GNU/Linux. connected via cable to router) to my laptop (OSX ElCapitan. connected via WiFi). It works like a charm if I use the laptop as the server; From ...
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How to list socket options of running processes?

Is there a convenient way (e.g. a readily-available command or a program that I can write using standard system calls) to list socket options (e.g. TCP_NODELAY) of an open TCP socket of some running ...