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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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Minecraft server using ngrok for port forwarding stopped working

So I built a PC using pieces I had laying around to make into a Minecraft server. I installed Ubuntu on it (I think it's the latest version because I installed it like a week ago. I didn't manage to ...
Chickenwings2x4's user avatar
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ARP request is successful, but TCP SYN is not visible in output of Wireshark

I was redirected from Network Engineering, hopefully below is in scope of on-topics. I have a TCP server, its properties are the following: It runs within a virtual machine (VMware). The host OS is ...
user94749's user avatar
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Linux netfilter: How to capture, modify and retransmit packets that my host is sending to a specific destination?

I am trying to write a linux service that captures the packets that go from my personal server to a specific destination and performs necessary changes to them. More specifically, i want to find all ...
hirad davari's user avatar
2 votes
1 answer
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Are extra flags discarded in TCP exchanges?

A "normal" TCP handshake looks like this: MachineA → SYN → MachineB Machine B → SYN,ACK → MachineA MachineA → ACK → MachineB This means that for each step, a flag (or set of flags) is ...
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How to explain sequences of FIN,ACK instead of FIN - FIN,ACK?

Context: newly installed Debian 12, I get a bunch of strange logs related to ssh: root@square:~# journalctl -u ssh -f May 07 11:13:00 yop-square sshd[766]: error: kex_exchange_identification: ...
WoJ's user avatar
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PowerShell: Diagnose timeout vs. connection refused on TCP port with Test-NetConnection

I frequently need to diagnose network connectivity issues and I'm currently using Test-NetConnection in PowerShell (Version 5.1). The output tells me if a port is reachable. In case it's not, I would ...
everdream's user avatar
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Delivery of packets to the correct web servers when they run in same machines

For example, I run two web servers in a single machine (only a single NIC available). They use different ports (let us say: 1200 and 1201) Now when a client (say from a mobile device or a browser from ...
user3103957's user avatar
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How does HTTP Keepalive handle multiple requests along with EOF from same origin?

says a client has multiple files to post to a server via HTTP Post method, there will be two api calls. since I don't want to create two TCP connections and I want to reuse TCP connection, so I use ...
user22155685's user avatar
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Linux 6.5 netfilter NAT reuses TCP ports in TIME_WAIT status?

In my understanding, Linux (netfilter)'s NAT doesn't reuse TCP ports in TIME_WAIT status, but seemingly Linux >= 6.5 reuses TCP ports in TIME_WAIT, even if the destination is the same. For example, ...
turgenev's user avatar
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How TCP handle mutiple concurrent requests from same host

Say there is a web server that exposes port 80 with two endpoints, one for returning datasetA, the other for returning datasetB. I have an application that does multithreading so I might send two ...
user22155685's user avatar
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How can I fix this? “XRAY: transport/internet/websocket: failed to serve http for WebSocket > accept tcp [::]:8443: use of closed network connection.”

Recently I bought a Germany based VPS server to create my own VPN using v2ray because I live in Iran and the internet is heavily censored here. I connected my domain to CloudFlare CDN to avoid my ...
Hamed's user avatar
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Explicit Congestion Notification (ECN), Why isn't the notification done by the Router?

Quoting from Wikipedia: "When both endpoints support ECN they mark their packets with ECT(0) or ECT(1). Routers treat the ECT(0) and ECT(1) codepoints as equivalent. If the packet traverses an ...
ConventionalProgrammer's user avatar
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1 answer
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Connecting delay on local network (SYN RETRANSMISSION)

Somebody knows what could be the issue? More often than not I can not connect instantly to my IP camera or local server and have a initial delay of around 10 seconds before it connects to the camera (...
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Ethernet connection loses upstream UDP and TCP packets but downstream UDP packets are fine

2 of my PCs are connected to my router like so: Both PCs' ethernet cables -> Switch -> ethernet cable -> ethernet socket -> ethernet cable from socket -> switch -> ethernet cable to ...
Molten Ice's user avatar
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Pgbouncer: Multiple Instances on same host receiving same TCP connection when using SO_REUSEPORT

I was able to setup two pgbouncer instances for database connection pooling, on a single VM (CentOS 7.0) listening to same port (6432) on two different TCP socket (I believe) using Linux Kernel ...
mediocre's user avatar
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Linux Server - Bandwidth test doesn't change during TCP Tuning process

I'm new to network administration and have a question. I am conducting research on whether it is possible to carry out TCP tuning using the genetic algorithm method. To do this, I wrote a Python ...
Mono Toad's user avatar
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Proxy tunnel without ssh?

I've gone down a bit of a networking rabbit hole recently, and I've seen people make their own proxy with ssh. I was wondering if I could do the same with raw tcp?
Theo Marcos's user avatar
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VirtualBox internal network will allow ping and traceroute but not nc

Update: tcpdump shows only ARP traffic with nc generating ARP traffic who has 192.168.254 tell 192.168.1.64 but tracepath says tell Fedora who has 192.168.1.5. 192.168.1.5 is pingable but 264 is not. ...
ArrowInTree's user avatar
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1 answer
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Difference between 100Mbps 1000Mbps INITIALIZATION-state

What is the physical difference between 10Mpbs, 100Mbps and 1000Mbps (BASE-T) INITIALIZATION. 10Mbps and 100Mbps does not use all of the 8C8P(RJ45) pins. Does 1000Mbps utilize the full 8 pins for ...
Aard's user avatar
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What kind of data structure is used by TCP to keep track of received and missing bytes for purposes of forming correct SACK numbers?

Say I have a client that successfully receives packets from server in the following bytes ranges: 0-99, 100-199, 200-299. The next packet 300-399 gets lost but the final one 400-499 is successfully ...
miran80's user avatar
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3 answers
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Understanding how ports work and how are they different from processes?

I've been a part of a network operations team for quite some time now and was extracting a certificate using this command: openssl s_client -connect <IP>:<PORT> </dev/null | sed -n -e '/...
Keshav Sehgal's user avatar
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Wireshark showing packet exchanges with unconnected IPs

Running Wireshark on a PC for network monitoring and I noticed something strange. Application data is being exchanged with websites that are not open in the browser, or on any other device on the ...
Instream's user avatar
1 vote
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Gateway responding with ACK instead of server. Causes RST

I have a service running on my LAN which works very intermittently. It serves a webpage just fine right after I restart the server running macOS 14.1 (I noticed this happening on multiple versions of ...
user1967944's user avatar
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2 answers
90 views

Can two client browsers use the same port to talk to a web server? [duplicate]

When a socket is created between a client and host, it includes the IP address, protocol used and port number of both. Suppose I have socket A (10.0.0.1, TCP, 50000) and (10.0.0.2, TCP, 50000) each ...
Jossie Calderon's user avatar
1 vote
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179 views

How to remove several Active Connections established by Firefox in the background to seemingly some local API server

When I checked active connection on my Windows with netstat -ab command, I found that Firefox has established several active connections to this seemingly local API. It had the name of a software ...
dashakol's user avatar
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1 answer
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TCP Port 999 Garcon

I did an NMAP today on Desktops at different sites. Some of those Desktops show TCP port 999 being open with Garcon. I then ran wireshark (5-10 mins) and saw no traffic going to/from it. Does anyone ...
NewGuyDavid's user avatar
1 vote
1 answer
1k views

Disable TLS 1.3 over TCP

After you create a website in Internet Information Services (IIS) Manager, in the config file in the path below, C:\Windows\System32\inetsrv\config\applicationHost.config You can modify the following ...
Codename K's user avatar
1 vote
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114 views

Why is TCP connection on Windows machines, retransmitting after receiving a correct ACK from HTTP server

Using two different Windows laptops, one with Win 7 and the other Win 11, I'm trying to connect to the HTTP GUI of a device (cell phone booster) that's connected directly to my laptop through an ...
Frank's user avatar
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What happens between a TCP handshake and HTTP CONNECT?

When you have a system making HTTPS requests through a web proxy, my understanding is that there is the TCP handshake between the client and the proxy, then the client sends a HTTP CONNECT to ...
andyc's user avatar
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1 vote
1 answer
510 views

Retransmission of TCP packets

I have device A (10.10.25.1), which is connected to device B(10.10.25.52) via unmanaged switch. Device A is a computer. Device B is measurement instrument. Device A is continuously(every 1sec) sending ...
Pablo's user avatar
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Windows can't connect more than 64k concurrency outgoing connection

I'm trying to make 100k concurrency outgoing connection from one pc to my local server. My program can use specific ip on each connection. Goal : 1 pc have around 100k concurrency outgoing connection. ...
ekomonimo's user avatar
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1 answer
563 views

How to disable TCP SACK in Windows XP?

Device 1 Windows XP. 192.168.101.173, I have access to the application code, but it is massive. Device 2 Embedded device. 192.168.101.205. I don’t have access to the code or even to logs from this ...
Beto's user avatar
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How to enable Windows 10 TCP keepalive?

As per this answer TCP keepalive can be enabled by three registry values. However, setting KeepAliveInterval=KeepAliveInterval=30000 miliseconds and TCPMaxDataRetransmissions=5 definitely does not ...
Pyotr Baykalov's user avatar
1 vote
1 answer
2k views

Print Related Communication - RPC over TCP vs RPC over Named Pipes

In Windows 11, version 22H2. Microsoft made some changes to enhance security, one of those is the change in the communication of print related operations. Making RPC over TCP the default for client – ...
Sergio Yepes's user avatar
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Miktrotik: disconnect TCP connection

I am working on a mobile device project. I have the mobile device connected on a local USB Wifi hotspot on an Ubuntu PC and I can WireShark the TLS connections which the mobile device creates towards ...
René Heuven's user avatar
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1 answer
791 views

How do I run a permanent tunnel in localxpose?

I am able to create a localxpose tunnel in ubuntu with this command: :loclx tunnel tcp but when I close my local connection to my server, the tunnel closes with it. Is there a way to keep a tunnel ...
Ddunlavy09's user avatar
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0 answers
60 views

TCP Receiver's Window stop increasing

I'm debugging a high-bandwidth TCP connection whose throughput is significantly lower than the capability of the device and the network. The network between these 2 hosts is expected to be high ...
Alex's user avatar
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1 answer
753 views

is it possible to OpenVPN connection UDP through SSH tunnel?

Hi i search a lot on the Internet, especially in this site and read more post and articles about using OpenVPN connection through SSH tunnel but all tutorials about using TCP protocol to do that. in ...
minttux's user avatar
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0 answers
677 views

wazuh agents cannot connect using cloudflare tunnel

I installed wazuh in docker on my synology which exposes the following ports: 0.0.0.0:1514-1515->1514-1515/tcp, :::1514-1515->1514-1515/tcp On the same machine (also in docker) i am running a ...
Felix D.'s user avatar
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Seeing several thousand retransmits every 10 sec. via iperf3 on TCP traffic through a propritary network bridge device

What is the most likely cause of TCP packet fastACKretransmits when testing with iperf3 on a small 5-7 node Linus AutoIP network running on a TI AM5728 board? Where and what setting should we check ...
RichardDQE's user avatar
1 vote
1 answer
3k views

UDP client to listen to a multicast group/port without setting its own IP?

I have a small microcontroller device that I program via USB using Python. The device has an Ethernet connection, which can be configured either with DHCP or by manually setting the IP/Subnet via USB. ...
Miki's user avatar
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5 votes
1 answer
808 views

Iptables Fail to block inbound from specific ip

Hi I Have a online server which i use like gateway and iptables is acting weird -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT -A INPUT -p icmp -j ACCEPT -A INPUT -i lo -j ACCEPT -A INPUT -i ...
denn0n's user avatar
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1 answer
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Http proxy server for unit test to connect to sftp through java

I am successfully able to connect to sftp over http proxy using paramiko library in python using ncat —proxy command Now I want to test it using java junit test. I am able to successfully create ...
abhishek bhardwaj's user avatar
2 votes
0 answers
422 views

TTL getting changed while pinging local network printer

When i'm pining a local device (NW printer) from win-10 PC using cmd, the TTL changing from 64 to 255 and again back to 64 continuously. Kindly share the probable cause for this. see below.. Reply ...
Yogendra's user avatar
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120 views

TCP splicer/splitter (proxy)

There's a big problem with satellite ISP's, that is shaping any TCP-connection to 4 Mbps. Since alomost any software uses single TCP-connection, resultinhg speed is limited. I've encountered ...
Nick Ali's user avatar
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0 answers
41 views

Teardrop detected from TCP ACK from myself

I'm experimenting with linux (Debian 5.10) networking to allow me to connect two networks (eg. 192.168.0.0/24 with 172.17.0.0/16) together. Setup In my case it is a small server with one NIC, hosting ...
0xCDCDCDCD's user avatar
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2 answers
307 views

Why do we need L7 reverse proxy for increasing the limit of max TCP connection to the backend?

I stumbled upon a YT video- 5 mins which explains that there's technically no limit to the number of connections that can be opened between the clients and servers even if there's a reverse proxy ...
asn's user avatar
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1 vote
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Windows8 drops network connection shortly after boot (but works if I wait)

I have a test lab which runs tests against Windows8 machine, more specifically a Pytest project which generates TCP traffic from my Ubuntu machine to Windows8 machine, and from the Windows8 machine ...
caffein's user avatar
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2 votes
1 answer
2k views

How to force `telnet` (in TCP mode) to send bytes immediately?

In Linux, when I run telnet <address> <port> and then type things, it buffers data and only sends collected line when I hit Enter. Furthermore, it buffers up to 4096 characters and ...
Nikita Kipriyanov's user avatar
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30 views

File service latency is high, How to troubleshoot?

This service is a file upload service and the request packet capture in the live network is as follows: The data uploaded by the client is halfway through, and then it will not be sent The server ...
zpzhuang's user avatar

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