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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TCP connection reset by RST during connect()

Does anyone have an idea why connect() would continue before the three-way handshake is finalized? According to what I captured by tcpdump the client sends a [PSH,ACK] with data before sending the ...
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connecting with external ip is extremely slow

To be clear, I am an extreme noob when it comes to networking, so please be kind. It takes an exorbitant amount of time to connect to my server (running on my home network) with an external ip (domain ...
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Is it possible to force Windows 10 to use higher TCP window scale?

I have two Windows 10 machines (bld 2004) I am trying to send data to between two sites. The sites average about 50ms RTT with no packet loss. I am having an issue where the max transfer rate I can ...
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How does tcp (on windows) decide which interface to use to route a connection to a server on the same subnet?

let's say I have a windows machine with two interfaces, ip1 = 192.168.1.10 and ip2 = 192.168.1.11 and I have a server listening for tcp connections on 192.168.1.12. if I have a program that makes a ...
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TCP 3-Way Handshake is merely OS responsibility?

While loadtesting an nginx (side B) with WRK (side A) i'm seeing a few TCPSynRetrans. For a 180sec run the number of TCPSynRetrans is less than 10 for around 400ish req/sec (according to wrk final ...
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Simulate network reset or failure in Windows

I have to check if my server application can recover from transient network failures. The application listens on some ports and is a client to backend services. I would like to run some command or ...
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How can I check if my wcf service is using NTLM or Kerberos?

My WCF service is hosted in IIS and communicates with it's clients via TCP (net.tcp binding), not http. I'm using Microsoft Network Monitor to monitor traffic on the server. I see the Protocol Name is ...
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How 2 dynamic (external) IP devices can talk to each other via 1 static (external) IP [closed]

I have 3 devices: Device 1 (Dynamic IP): A raspberry Pi sending UDP packets to Device 2 via 4G modem via Internet Device 2 (Static IP): My Ubuntu/Windows PC with static IP, successfully receives ...
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Creating VNC session on specific port fails even though the port is clear

Sorry in advance for the huge amount of command output text, I thought it would be more clear than paraphrasing myself. I am using CentOS 7 and tigervnc: (base) [carlos@pulsar .vnc]$ cat /etc/centos-...
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Network performance issues between Windows/Hyper-V and remote Linux VM

I'm in the midst of migrating an application away from a Win2k16 server but it seems the win server doesn't agree to the plan. When migrating the data, I realized that performance is incredibly bad, i....
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Two way handshake for WHOIS protocol? RFC 3912

From RFC 3912: 3. Protocol Example If one places a request of the WHOIS server located at whois.nic.mil for information about "Smith", the packets on the wire will look like: client ...
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Weird networking issue with TCP 3-way handshake

I am facing a weird behaviour while trying to connect to a HTTPS server. I have a PHP SOAP Client which runs throught Apache2 that can not connect to the server: 10:15:19.871149 IP 1.1.1.1.57038 > ...
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Why am I not receiving a response when the request is sent through a load balancer and the response is too big to fit into a single packet?

There's a certain condition where I'm unable to receive a response from an HTTP request to a particular service: the request is sent through a load balancer and the response is too big to fit into a ...
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Windows IIS to IOT cell device, am I able to cap TCP packets?

I am dealing with some IOT devices that I have little control over, but need to serve some files to. The IOT devices are initiating TCP/IP connections with order-of-magnitude too-optimistic window ...
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Telnet connects to server but cannot transmit data

Our client has a server and our web apps run on port 443 and 2000. Our client has two groups of IP addresses. One group is for the computers used in the company building. These computers can browse ...
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TCP/IP packet transmission through NAT

Why my TCP packets do not reach the destination? I send http requests from one PC to another PC, both behind NAT: PC1 behind NAT1, runs Wireshark. PC2 behind NAT2, this one sends http requests. To ...
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Are there STUN implementations that can sometimes handle symmetric NATs?

I've been working on connecting two devices that are each behind a symmetric NAT and managed to make it work quite consistently. However, it takes quite some time for the connection to happen (...
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Kernel TCP stack not forwarding packets immediately to remote server

I'm trying to figure out why a single HTTP POST request over a re-used TLS connection is still taking roughly twice the roundtrip time (RTT). The client is running on Debian 10.8 within a container on ...
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Connection and reception are slowed by FIN_WAIT

I am using mosquitto as a broker to exchange data between clients using the MQTT protocol. But recently I have the following phenomenon. My mosquitto sometimes connects very hard and sends it too. ...
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How to delete IPv6 DNS Servers via command line?

I can successfully delete IPv4 DNS Servers via command line on a Windows Server 2019 with the following command: netsh interface ipv4 delete dnsserver "My Ethernet" all After this command I ...
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When connecting from one subnet to another through a WireGuard VPN, why TCP requires NAT on both sides but ICMP works without NAT?

I encountered this issue today with the following setup: [Cloud Server] --> [Cloud Gateway Server] <- WireGuard -> [Home Router] <-- [Home Device] I have source NAT on my router. My home ...
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TCP: Why would I get a PUSH+ACK after sending RST

I'm rolling out my own web server and I rely on TCPDUMP to see whats happening behind the scenes. The server address is 192.168.7.2 and the client is 192.168.7.1. I used curl (and also tried wget) to ...
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SSH Port Forwarding not working on remote server

I am trying to SSH into a server for testing an API. I had been working on it for the past 2 weeks, and it was working fine. No issues as such. The command I was using to ssh was: ssh -L 8000:...
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TCP checksum errors between linux apps and NICs

I'm writing an internet application and I'm at the stage of crafting my own TCP packets. Except there is a major problem. According to the TCPDUMP utility in linux, every tcp packet that I send out ...
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huge difference in RX bytes vs TX bytes (ifconfig) on Syslog-NG server

we have a syslog-ng server acting as an intermediary logger. the server receives data from all devices on the network (from many different sources, on both UDP & TCP ports), filters them a bit, ...
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When a website is hit from two different browsers running on same computer. what are the properties that differ?

Here they are hitting the same DNS and port. how does the client know those are two different browsers. And how does the client differentiate those connections? I heard this question from one of my ...
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FTP rule for NACL in AWS

I need to connect to an external FTP service that resides outside of my VPC boundaries. I added an outbound rule to a specific IP address and both TCP ports: 20 and 21 Do I need to add and inbound ...
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tcpdump: invalid cksum from client to localhost interface even after disabling offloading

I'm having a strange issue. In linux I have two windows open. one running tcpdump and one running curl. I used curl to try to make a connection to local host and tcpdump logs invalid checksum errors. ...
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Apache keeps TCP Connection in CLOSE-WAIT state for 600 Seconds

My setup consists of two apache servers like in this diagram: |Apache | >==Reverse Proxy Connection====> |Apache | |Server1| <==Response through conntrack==< |Server2| After a successful ...
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Troubleshooting TCP (but not ICMP) packet loss

I have server A and server B, with A attempting to open TCP connections to server B. curl shows that approximately 5-10% of connection attempts time out. mtr shows 0% loss to B, and at intermediate ...
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Linux TCP stack does not send a RST after giving up on retransmissions

Several sources (one being my colleague and the other being TCP/IP Illustrated by Stevens) indicate that there should be a RST sent after the TCP retransmission attempts have been exhausted. I have ...
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How to limit the total volumn from a TCP connection

I have a particular application with one type of connection that mostly sends packets to clients while receives nothing but login request. (i.e. video streaming) Therefore I want to limit the Total ...
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Stunnel for Service IPC over TCP?

I am working with an application that consists of Windows Services on the same server sending messages to each other over TCP. Each service is assigned a port on which it listens for messages. I ...
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Use of :80 in proxy URL

Setting some Squid proxies up, and trying to figure out some behavior. Squid in a pass-all configuration, with the linux node set to forward 80 to port 3128, which Squid is listening on. I do have an ...
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10 NICs in 1U box - possible?

I am looking for a device with 10 NICs in one 1U box. The CPU can be anything even a microcontroller as long as it can process TCP packets. I would prefer a sort of Linux on it but is open to other ...
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Apache LB and huge amount of close_wait connections

I use apache as a loadbalancer for servers with some java apps. On the apache host I saw huge number of close_wait state which was around 2500. Is it a problem with apache itself or with app on the ...
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How to calculate average RTT of my clients

I want to calculate the average RTT of my clients when they are trying to establish a connection with my server (let's say a web server on port 3000), is there any ready tool or Linux command ? or is ...
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Which setting is limiting my active connections (ip_conntrack)?

I have a webserver with ispconfig (mysql & php & nginx). My munin statistic shows that there are the connecitons limited to about 9k. But I can't find a settings which is about 9000 which I ...
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nginx TCP forwarding with GeoIP

CentOS 7.8 nginx version: nginx/1.18.0 yum install nginx-module-geoip yum install GeoIP GeoIP-data Then, GeoIO runs well with HTTP(S). I need nginx to forward a TCP port, which is only open to CN add ...
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Using netsh to portforward to a VPN

I have a VPN client set up on my Windows machine connecting to a VPN elsewhere. I have a small embedded Linux device on the same local network as my Windows machine which needs to communicate through ...
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Delay TCP SYN retransmission on Linux

Our application connects to a device on a radio network. The network has to wake up the device before it can communicate which takes about 3 seconds. In this 3 seconds our CentOS (Linux 3.10.0-957.62....
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URL redirection and TCP proxy in haproxy

In a server with only one ipv4 and running haproxy, i want to redirect an url and proxy another in TCP level, for ssl passthrough purpose. frontend https-frontend bind *:443 mode tcp option ...
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What is TCP-over-TCP and how does OpenVPN under TCP mode avoid the issue?

This article explains why TCP-over-TCP could be a performance disaster. My understanding about the issue is that the 'outer' TCP connection deals with packet loss and congestion of the network and ...
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Redirecting all outbound traffic to loopback for VPN program

I haven't been able to find much information on how a VPN would work from a programming perspective. I figured you'd have to reroute all packets from localhost to a local application, and therefrom ...
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TCP modification in-the-middle and acknowledge number

For some private purposes I need to enrich HTTP header with additional information (which will be handled by app on the HTTP server side). The basic idea was to modify received packet, send it to ...
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How can I isolate a single TCP connection on Wireshark?

I just started using Wireshark for network troubleshooting purposes and I am a little confused about one thing. I requested a webpage and for the next 10s I monitored the data. I then used the filter ...
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“An existing connection was forcibly closed by the remote host” when trying to connect to azure sql server

I'm trying to deploy a SQL database to my azure SQL server. When I'm trying to connect to my target server, I get the error listed below. I'm using Microsoft SQL Server management studio 18 with ...
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How to investigate TCP memory leak

We are running a medium size AWS EKS cluster (~120 kubelet nodes) running mostly Go services. The services deployed in the cluster are quite busy, handling millions of calls per hour. Each kubelet ...
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TPROXY iptables with transparent-proxy and server in the same host

I'm trying to test a scenario as described below: Client[eth0] ----[eth0]Server Client's eth0 interface is configured with IP 10.10.10.1. Server's eth0 interface is configured with IP 10.10.10.10. ...
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apr_socket_recv: Connection reset by peer (104) with ab stress test

I've been testing the AB on a server at Digital Ocean for multiple concurrency using mpm_worker as the thread controller. mpm_worker config The AB has the error message: apr_socket_recv: Connection ...

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