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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.

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Checking Nagle Algorithm on opened socket

One of the platforms we use opens TCP sockets (No source code available). I need to check if the Nagle Algorithm is disabled or enabled on those sockets. The operating system used can be Windows or ...
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Why is my TCP connection attempt via PHP acting weird?

I'm not sure if this is better here or on SO but since the issue isn't in the programming I figured it applies here (or on U&L or on serverfault, but I guess/hope I'm fine on here). I want to ...
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Wifi-Lan Port blocking

I'm writing a paired (windows) server and (android) client application suite that uses TCP connections over wifi on a funny port number. The Server advertises its availability using Bonjour/Zeroconf. ...
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1answer
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why can't we just upload a file and it reaches its destination without the other device downloading it? [closed]

when we have to view or get some content off the internet. We have to download it on the other hand the server uploads it So here's my question => Why can't the server simply upload the file and it ...
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Does HTTP as a protocol include any mechanism for guaranteeing information?

I asked this question on networkengineering.stackexchange, without realizing that any protocols on top of TCP were off topic (i.e. that only OSI layers 4 and lower are on topic there). The question ...
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1answer
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Does a remote TCP Server has to run on Public IP address only

I have interfaced a GSM (Uni4 SIM800) module to a Raspberry-pi-3B module using AT commands to run a simple TCP server, and another pair of GSM and Rospberry-pi to run a TCP client. Now the Telecom ...
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1answer
23 views

VPN not connecting to a specific site

I've been using NordVPN for quite some time, but sometimes when the VPN is on certain websites become unreachable with a timeout error. For example, https://g1.globo.com is only accessible when the ...
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Does TCP Nat hole punching requires both router to support

I've heard that TCP Nat Hole punching only support some type of router. For example ZyXel won't support TCP Nat hole punching while Linksys support it. What happened if I try to connect between a ...
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1answer
68 views

Getting a UDP-only VPN to work over TCP

For a project of mine, I'm searching for possibilities to have a UDP-only VPN working over TCP (preferably on port 443 or 80). I have found the following while doing some research: This is possible ...
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48 views

Changing the TCP initial congestion window value in Windows 10

I would like to do some testing with the TCP Initial congestion window on Windows 10 Pro, but it seems the settings are disabled in the Pro version: Set-NetTCPSetting -SettingName InternetCustom -...
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19 views

Frames above 2000 bytes not acknowledged by the client/receiver

I working on adding a jumbo frame functionality to my application. My problem is that I receive no ACK for frames with payload above 2000 bytes. My system looks as follows: the server sends requested ...
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Need help figuring out a random connection timeout issue on a server

I discovered this issue trying to loadtest a custom node.js websocket server, where some sockets are failing to connect (they hit the connection timeout). It does not appear to be related to the ...
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Short description of the difference between TCP and IP [closed]

I am learning about TCP and IP but there is a lot to each of them and it will take a while to organize the concepts around them. I'm wondering though if one could briefly describe how TCP and IP ...
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30 views

TCPView: [System Process]

In TCPView I get a lot of connections listed under the Process column as [System Process]. These connections cannot be terminated, and cannot be whoised. How can I find out what programs started ...
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47 views

RTSP - continue recording after network issue

I have a problem with capturing RTSP stream over TCP from IP Camera. I tried many options like timeout, stimeout, other flags related to key frame etc, nothing helped. FFmpeg is capturing stream ...
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How to create persistent TCP connection “proxy”?

I need to create some kind of TCP proxy to maintain persistent connection from one side. CLIENT --[persistent]--> MY_SERVER --[reconnect]--> THIRD_PARTY MY_SERVER should maintain persistent ...
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Changing the TCP Destination address using WinDivert or PyDivert

I'm trying to "route" TCP traffic by using WinDivert to change the Destination Address (and port) of certain outbound traffic. I began with using PyDivert as I am a total and complete programming ...
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TCP traffic not working through Iperf tool in ubuntu

I am using system-A(interace name:tun0; IP: 192.168.3.1) and system-B(interface n ame:ss200; 192.168.3.2) which run on ubuntu. When I try sending traffic in TCP mode from A to B or vice versa, by ...
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1answer
48 views

Practical (vs theoretical) max limit of TCP packet size

I'm a web developer who is pretty new to the industry. I was presented with a coding challenge for a job interview where I need to design a messaging system and architect a system for how it deals ...
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1answer
197 views

TCP reset (RST) flag

I am trying to stream a video between 2 hosts also I am trying to simulate changing IP scenario, the client started listening to the server then I moved the client to the new switch and it is got 192....
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297 views

netstat Foreign Address shows my hostname, TCP sockets refuse connections

I am attempting to establish a TCP connection to a Windows machine running some third party software, unfortunately, I can not make the connection succeed. Running: netstat -an Shows my service is ...
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0answers
22 views

HTTP Video streaming failed because TCP re-transmission

I am trying to stream a video between 2 hosts but I am trying to simulate changing IP senario by listing to an IP (192.168.2.3) instead of the real IP(192.168.2.5), I am using mininet and Ryu ...
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1answer
540 views

How to immediately kill orphaned TCP connection?

Closing orphaned TCP connections is surprisingly difficult in Linux. This issue has been raised here, here, here, and here; however, neither of the approaches worked for me. Calling close() doesn't ...
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1answer
104 views

how to open tcp connection in fish shell

I am looking for a way to open TCP connections in fish shell. In bash, I can do the following to open a TCP connection. This is quick telnet type test when telnet is not installed. $ echo > /dev/...
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2answers
133 views

How to use nc to listen on a TCP port indefinitely?

I want to read the data arriving on a specific TCP port indefinitely and dump the data into a file. I have tried many different variations of nc but it is not working out for me. For the most part I ...
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1answer
198 views

Which protocols (TCP or UDP) consume more %CPU?

I'm sending data from the client to server using IPERF3, fist I used TCP and then UDP. I observed that maximum time TCP consumed more %cpu than UDP. Generally which one suppose to consumed more %CPU? ...
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Can't stablish TCP connections into a Hyper-V Centos VM

I've set up an internal network with a VPN gateway on Hyper-V on Windows 10. It works fine in the sense that all VMs can communicate with one another and with the external world. The problem happens ...
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1answer
76 views

OpenVPN doesn't forward HTTPS traffic, HTTP works fine

I have an OpenVPN server running on a Raspberry Pi, and I'm encountering issues trying to connect to HTTPS sites using it. I can connect to HTTP sites (confirmed via nc example.com 80). From the ...
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33 views

Cannot Connect With PC Which Is Using VPN Through TCP

I am working on simple client and server program to make communication between devices. The scenario is: PC1: This PC is running server version of program. This PC connected with Internet (...
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1answer
32 views

How to configure OS to re-assemble TCP segments

I have an application that is reading in TCP data from a socket. The sending device is sending out a full 1400 bytes of data to the server's socket on the other end. Somewhere along the way, the ...
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24 views

Why TCP scan is more reliable that SYN scan?

I heard that the TCP connect (-sT) scan in Nmap is much sure than the TCP SYN (-sS) scan. But why ? Does the TCP SYN scan generate false positives which is not the case for the TCP connect scan ?
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1answer
28 views

Port forward traffic from restricted network with home unrestricted

Here is the scenario: I have an enterprise e-mail whose SMTP server listens on port 2525. I can configure an e-mail client like thunderbird in my home without any problem. I also have another job, ...
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in Debian server, IPTABLES PREROUTING behave differenty for different ports

I have following three rules in my iptables firewall -A PREROUTING -i eth0 -p tcp -m tcp --dport 12346 -j DNAT --to-destination 11.207.2.4:12350 -A PREROUTING -i eth0 -p tcp -m tcp --dport 12348 -j ...
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How do I make ppp reliable over lossy radio modems using pppd and tcp kernel settings on debian? [closed]

I am having a lot of trouble establishing a reliable ppp / tcpip link between two debian systems over radio modems. My hardware topology is a little complex. The system uses: Raspberry Pi 3B at ...
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28 views

TCP sessions limit over bridge mode

I have an iDirect satellite modem (X5) which is limited by only 1500 TCP sessions and it doesn't support bridge mode, but they have other modems that support it that I could purchase. My Question is, ...
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What is TCP's three way handshake response to old connection?

Lets say we have two hosts (A and B). How does the three way handshake process prevent a old SYN-segment from A to connect to B. It starts with A sending a SYN to B, and then B responding with?
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Destination Host Unreachable between linux boxes

I have a home wifi network with 2 linux and 1 mac system. I can reach each linux from mac and other way round, but an attempt to ping a linux from another linux results with "Destination Host ...
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1answer
45 views

tcp session - http request [ x out of y] in wireshark capture

As below, i am seeing this [HTTP request 1/2] and [HTTP request 2/2] in 2 separate payload, are they separate GET request in a single tcp session or are they the same GET request ??? ==== Added full ...
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1answer
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Redirect with a port

We want to launch a little Minecraft server community, With one server for a forum, another for the Minecraft server. I know how to make a subdomain for the MC server but what I want is to have the ...
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1answer
646 views

What means “Communication administratively filtered”

I am facing a problem in a foreign country reaching a special server per TCP/IP. ICMP is no problem but it looks like the dialup access provider is somehow filtering the TCP port 25 (SMTP). I get a ...
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1answer
459 views

TCP spurious retransmission and duplicate ACKs for Virtualbox guests when bridged

Using Virtualbox 5.2.8 on Windows 10 Pro 64 Bit I noticed that sometimes TCP connections stall. The guests are Linux (various distributions). When I investigated the issue I found that this happens ...
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1answer
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What are network ports internally? [closed]

I know there will be multiple ports in the host/computing machine for each of the services that i hosts on the network. But i want to understand what are these ports internally? Below is my ...
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4answers
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How to send binary data in netcat to an already established connection?

I can do the following to send binary data in netcat: echo -e '\x80' | nc host port But I don't want to do it like this, what I want is to connect to a server: nc 192.168.1.115 12345 And then send ...
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383 views

How to make tcpdump display only source IP, destination IP, ports and timestamps

I am running tcpdump to track traffic on 2 interfaces, one input and one output. The sole purpose is to measure the latency between the time when the input interface receives incoming TCP traffic and ...
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38 views

RST hijacking good ACK number

I'm trying to perform a RST hijacking sur on my Virtual Machine. I have 3 Vm's: -attack : 172.10.10.11 -victim : 172.10.10.21 -pirate : 172.10.10.31 First, I connect from attack with telnet to the ...
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TCP Selective ACK (SACK) never works and Delayed ACK (DelAck) only occasionally works on inbound traffic, but OS is configured to support both

Performance graphs from Windows Performance Monitor show that: For all Internet connections tested only except my ISP’s speed test page, the number of segments sent (nsend) ≈ the number of segments ...
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1answer
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How many connections can OSX support?

I'm using FTP software and it has an option of using 1-30 connections for uploading. How many connections (internet) can an operating system like OSX make and how do I know what value to choose? I ...
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1answer
93 views

Can I bypass layer 3/IP to send a TCP packet?

As I know We can just use a Ethernet/layer 2 address to communicate with LAN device. But for a WAN device IP/layer 3 address is required. so TCP is in OSI 4th layer above IP layer. my question is can ...
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1answer
88 views

sudo netstat -antp not showing PID

i am testing stuff with sockets and i encountered that strange case : i coded i very simple tcp server in c, i made it block after accept(), just to see what happen when accepting multiple connection ...
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1answer
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identify individual devices from aggregate traffic of router

Is it possible and if yes how to identify individual devices (laptop vs. mobile phone vs TV) when listening to the aggregate traffic of a wifi router? Assumption: all devices of interest are ...