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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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Is it possible that FTP makes any bit error?

I have been thinking so far that FTP deosn't cause any bit errors while transferring files. But recently, I met a problem that the files I sent through FTP between my two servers are sometimes ...
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Retransmission in less than one second

On my Linux machine I use nc to communicate with a echo server running on my android device. I use nc to send text to port 65303 of the android device. After entering test1 the same text is sent back ...
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Why does my internet connection only work properly with a UDP-based VPN?

My house is connected to the main router in another building via a single LAN cable that is run partially underground, partially outside (along the wall of the house). There is one switch on the route,...
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Where is the iptables MARK location in TCP package?

In my CentOS7 Server, I emptied all the iptables rules, and then add below rule: iptables -t mangle -N DIVERT iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT iptables -t mangle -A ...
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Conflicting netstat results

I'm doing a project where I'm trying to capture any process on Windows attempting to communicate through TCP ports 587, 465, and 2525. I have experimented with several parameters for netstat for this ...
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Protocol Mismatch ngrok & netcat

When I create a tcp tunnel with ngrok and I try to communicate with nc I receive a message saying "Protocol Mismatch" Explain Better: I use macOS 12.3. I launch ngrok tcp 9999 on a terminal ...
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2 answers
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unable to establish TCP connection with server (Java)

I have been trying to connect to my own Java TCP application, which is running on a rented server with static public IP. Scenarios that work: server runs host app, and servers from https://check-host....
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2 answers
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What is the corresponding TCP states for states in iptables? (NEW and ESTABLISHED)

The iptables manual says ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, NEW meaning that the packet has started a new connection, or ...
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How can I assign an ephemeral port range to a specific linux service and not the entire IP stack

For example: If I want sshd to listen on 22 but use ephemeral ports of tcp 50-60 for communication.
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1 answer
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Relay TCP upload traffic and make download traffic go directly to the client

This is a supplement for iptables SNAT for UDP rule is only applied to some traffic In fact, I have three machines: the client the target server the relay server What's my motivation for doing this? ...
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bitcoin-cli testnet : Could not connect to the server 127.0.0.1:8332

I've installed bitcoin-cli from here I run the bitcoin core on Ubuntu 20.04 (AWS EC2). mac-os also experiences similar problems. Ubuntu 20.04 screen capture for the error messages The commands I've ...
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Meaning of IPTABLE duplicate values

I'm new to IPTABLES and when I execute the following command /sbin/iptables --list -n | grep 16381 I could see multiple entries as shown below : ACCEPT tcp -- a.b.c.d 0.0.0.0/0 ...
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-1 votes
1 answer
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How do computers know how to use TCP

I'm asking from a Windows perspective but any perspective is great. Are NICs all a computer needs to interface with TCP? Wouldn't they also need some sort of software associated with TCP, or is that ...
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What ports range is safe from taking by Windows 10

I wrote small program and I would like to use some TCP ports. Same ports for a longer period of time. The problem is each time Windows 10 wakes up it makes its mind which ports to reserve for its ...
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is TCP handshake handled by web application flask or web servers like nginx?

if I run a simple flask application in development mode(so web server and web application is the flask library) on port 5000. is there a way to see SYN, SYN-ack, ack requests that are exchanged ...
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Sending PJlink commands with netcat

I have a projector that I want to control over TCP using a protocol called "PJlink", but I can't manage to get it working. I'm currently trying to do this through Windows Terminal in WSL ...
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Block outgoing connection from server to Internet, but enable specific TCP port access from outside

I am using Mikrotik RouterOS on a Mikrotik router. There is a server in my network from which every outgoing connection using every protocol should be disabled. I achieved this with a following rule: /...
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Server hello is not returned without SNI

I've setup a proxy server (squid) with https_port enabled. When I send requests to this server using a url like domain.com or even using a host alias (i.e. manually written in /etc/hosts), there's no ...
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2 votes
1 answer
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Terminated HTTP/2 connections on macOS in Inea ISP

We’ve had a discussion about my issue on Reddit, but I wanted to try here too. I have a symmetric 300 Mbps fiber connection at home and sometime in September/October 2021 I’ve started seeing weird ...
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What handshakes happen (or need to happen) when I connect my FPGA with Ethernet cable to my home router+modem device in one of its ethernet port? [closed]

I have a FPGA edge device. I want to send and receive ethernet packets to my laptop through the router+modem device at my house. My laptop is connected to the router+modem through the wifi (for ...
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Are there any alternatives to tracert command in cmd/PowerShell that doesn't suffer the request timed out issue?

The cmd tracert <URL> command, quite often, suffers the request timed out issue if the ICMP packets/port are blocked by the routers/ISP's firewall. Now I was wondering if there is any cmd/...
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What ends a TCP stream?

I am using WireShark and went to google.com. I got 23 TCP streams,23 TCP conversations, 23 handshakes right? I know that the TCP streams end with FIN Flag and that TCP segments are encapsulated in the ...
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Keep alive SSL client connection with socat

I want to know if it possible to detect a dead connection with socat openssl client. I am establishing a reverse shell with socat this way: socat "openssl-connect:api.hoposhell.com:10000,verify=0,...
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The handshake operation timed out

I've mbedtls nonRTOS server device. I'm trying to communicate with PLC Client. But before the using PLC, I'm trying to use python tls client. I've a problem with when I use below cert and key file ...
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iptables TCP oneway data

I need to set firewall to allow data in TCP connection in one way only (outgoing), back only ACK (incoming). What is the right solution? Some --tcp-flags or size of pockets or something else? Thanks ...
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1 answer
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TCPView (Windows) doesn't show any addresses

I'm using TCPView 4.16 for Windows 10 (downloaded from https://docs.microsoft.com/en-us/sysinternals/downloads/tcpview). Up until a few days ago it worked fine, but all of a sudden it simply stopped ...
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Device communicates with server through bridge, unable to capture all packages

I'm trying to reverse engineer a device to be able to access its API locally. Currently it is communicating with an online server, where I can log into to see its data. Set up The device connects ...
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Google and Youtube websites open even when Port 443 is blocked

I want to prevent internet access to one PC retaining the file and printer sharing. For this, in Windows Firewall, I created a rule for Outbound Connection and blocked Ports 80 and 443. After enabling ...
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What might be the easiest way to append a <CR> to the end of an ASCII-formatted command?

I am using a piece of NDT inspection software to communicate with a digital IO peripheral. The peripheral takes ASCII commands over the local network. Unfortunately, the software seems to be incapable ...
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Can TCP implementation send several packets without waiting an ACK for the first one?

I basically know who TCP works from sockets point of view, but I can't figure out some thing. Suppose I have now 1000 bytes to send, it comes for TCP-stack internal buffer and gets sent. These bytes ...
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How to determine what application is sporadically sending tcp/udp traffic (peerblock) via state changes?

I use peerblock (which isn't the best, but it's something). Anyways. When I'm not downloading anything. Peerblock activity drops to almost non existent, but occasionally I will see something pop up ...
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1 answer
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How can I identity which process is sending data to a certain host on Linux?

As per title, I want to figure out the process responsible for certain traffic. I can see the traffic in wireshark, but I don't know which process it is. Is there any straightforward way to do it? I'm ...
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1 vote
1 answer
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Prometheus Blackbox Exporter TCP probe returns value of 0, even when port is open (Iperf3 server)

I have a strange problem that I've been digging into the last couple of days. The setup I have an Iperf3 server running in Docker on this internal address and port: 10.10.2.2:5201 I also have ...
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6 votes
2 answers
8k views

how to access windows localhost from wsl2?

I have windows 11 with wsl2(ubuntu) installed on it. I've setup a gdb listener server on my windows localhost and want to access it from wsl2. but it seems my windows machine and wsl vm are using ...
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Wireshark is not display the packets between the client and server

On my machine there a TCP server is running @port 54000 which is a echo server it sends the same message which is sent to it. I have multiple clients which is connected to this server. Clients and the ...
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4 votes
2 answers
42 views

linux service TCP Gateway with service starting

Is there a service (linux) that starts the service on an incoming TCP request (if it does not already exist) and then forwards it to the application? For example, for a docker container that would ...
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How do I get traceroute to work like tcptraceroute?

On Mac OS 11 the man page for traceroute says you can set it to TCP mode with -P TCP. When I attempt to do this I get no responses: [me@laptop ~]$ sudo traceroute -f 6 -m 10 -e -P TCP -p 443 www....
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Block incoming TCP packets for Windows

I have a test setup requirement where I want to block incoming packets from the server to my windows machine. I am trying to do that using the following command netsh advfirewall firewall add rule ...
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Returning tcp/udp packets to sender

I'm using a Linux machine with WiFi hotspot to test the WiFi stack of an embedded device. For context, the embedded device is designed to send and receive encrypted packets to/from a remote server. To ...
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-2 votes
1 answer
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How to investigate why a computer stops a TCP connection?

I've just written this question on another StackExchange site, but I was advised to ask the same question here. I would like to broaden the question: how can I know why a host closes a TCP socket ...
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Kubeadm - unable to join nodes - request canceled while waiting for connection

Trying to provision k8s cluster on 3 Debian 10 VMs with kubeadm. All vms have 2 network interfaces, eth0 as public interface with static ip, eth1 as local interface with static ips in 192.168.0.0/16: ...
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1 answer
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Address of a Transport layer?

In TCP/IP protocol stack following protocol level addresses exists: Data Link layer - MAC address Network layer - IP address Transport layer - ? Application layer - Socket address which is ...
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1 vote
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TCP server device for USB access readers

I have a BarCode reader that spits out data over a Virtual COM port (RS232 Serial) through a USB cable. I have a server running and managing a facility, and I need to read data coming off the BarCode ...
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How can I do a bi-directional Port-Forwarding (flow encapsulation)?

I have two applications: a client and a server which communicate through port 1234. For some reasons this port is blocked on our system but everything works correctly on port 1235 (checked with two ...
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TCP ports of Windows 10 PPTP VPN server

I have installed the PPTP VPN server on Windows 10 machine (incoming connection feature), I have created the NAT on port TCP 1723 and UDP 1701 in the router. In the server machine there was an apache ...
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1 vote
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What's the minimum upstream bandwidth required for ACK packets in a TCP connection?

Consumer internet connections often feature asymmetrical bandwidth with just 10% of even 5% of upstream speed compared to downstream, for example 1000MBit/s downstream with 50MBit/s upstream speeds. I ...
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How to show a HTTP stream from VLC Player in Wireshark?

I just set up a HTTP stream of a video between my Server and Client system using the VLC media player (using the command line). Both the systems run Ubuntu 20.04 vlc -vvv <path to video file> --...
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0 votes
3 answers
124 views

Connect a socket to another PC in same NAT

Hey I've got two machines on the same network. They get their IP info back from an external webserver. Same IP due to NAT but different ports locally. Hmm that's weird.. they can't socket up or even ...
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2 votes
1 answer
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Why is the TCP MSS (Maximum Segment Size) 1460 bytes?

I'm wishing to know why the MSS value in the TCP header is 1460 bytes. I know that the MTU for Ethernet networks is 1500 bytes, that the IP header is 20 bytes and the TCP header is 20 bytes...but ...
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2 votes
1 answer
75 views

Mysterious TCP/HTTP issue accessing LaserJet Web Interface

I'm trying to diagnose a connectivity issue between my LaserJet M551dn (lj500) and my FreeBSD system (hal9k). The problem is that I can no longer browse the LaserJet's Web Interface (times out after ...
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