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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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TCP communication on port not responding on different Availability Zone or Subnet

I'm a little curious and confused about this situation. We setup a monitoring instance scraping an exposed endpoint on 2 different instances. Both on same VPC, same security group, same route table ...
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UFW route not responding

Hi i tried to make a server where every software running on it is in a vm. i tried using ufw to route the requests and it worked ... locally. when i tried to connect to one of my vm using a vpn i saw ...
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The packet goes through the other router

I want to connect two hosts in parallel with two different models of virtual routers. These are made redundant by VRRP. Originally, packets are sent through only one of the routers. However, when the ...
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TCP slow start and duplicate ack

In TCP slow start, what happens when 3 duplicate ack is received. I am aware of the recovery process in congestion avoidance, however I read a blog post that if 3 duplicate acks are received in slow ...
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Dangling ssh sessions when my laptop goes to sleep

When I get up from my laptop (a Mac with MacOS Big Sur) for long enough that it "goes to sleep", my interactive sessions with ssh servers are broken. That is annoying but I could live with ...
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2 votes
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Dovecot claims ports are in use, netstat disagrees

Attempting to start dovecot gives me this: Apr 28 13:37:00 master: Error: service(pop3-login): listen(*, 110) failed: Address already in use Apr 28 13:37:00 master: Error: service(pop3-login): listen(*...
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Having Trouble Identifying TCP Congestion Control Provider option: Default

I am running a Windows 10 (Version 1909) OS and when I am entering the following command in CMD ... netsh interface tcp show global ...I am able to see add-on congestion control provider set to "...
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Bytes-in-flight higher than receiver window in frozen client connections

I am dealing with sort of a "ghost issue". We have an endpoint URL that some people can use at all times with no issues but others have a frozen connection on the client side (checked with ...
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Could someone please explain the difference between these expressions

drop proto tcp and not (dst port 80) pass proto tcp and dst port 80 Is there a difference between them?
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haproxy SSL/TLS Passthrough Proxy not working?

I want to setup haproxy as simple tcp-proxy. Below is my configuration. When I try to send e-mail via Thunderbird(pointing smtp to ip_of_my_host:8123) or simple python script I get an error about not ...
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No SYN-ACK Packet from server

I have two servers and I used my own embedded system with LwIP to do connection to these server. My embedded system with LwIP is the client and I have server1 and server2. I connected to server1 and ...
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How to find the symmetric key algorithm being used for a TLS connection in Wireshark?

I'm doing a TLS Wireshark lab and I can't find any information in Wireshark, the lab, or online how to find this answer: What symmetric key cryptography algorithm is being used by the client and ...
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Windows Network Limited Throughput with Occasional Very Slow Start

We have a 1Gbps (up/down) Internet link at work and I noticed performance was terrible when communicating with our servers in the Cloud. By terrible I mean, out of the theorical 1000Mbps, we were ...
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HAProxy: Defer TCP connection to backend only after first data arrives

I'm trying to understand if haproxy 2.2 or greater has a specific configuration that allows to defer opening the tcp connection to backend servers only after the first data segment is transmitted from ...
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How to get syn flags, ack flags, sequence number and acknowledgement number in tcp packets with nfqueue?

I am working on a project which can redirect the network traffic in tcp (packets sent by client to server1 will be redirected to server2) with netfilterqueue, so I need to classify the packets by ...
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localhost loopback tcp connection in Windows: increase the bottleneck of 65535 bytes per segment

The scenario that I have is as such: I have a loopback TCP session and I want to improve its performance. I have my socket-like objects (System.Net.Sockets in .NET Framework, to be specific) sending ...
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Network drive on windows 10 host inaccessible to client using net view and net use commands

I apologize ahead of time, I am new to networking and I obviously don't understand everything yet. Please have mercy on me. Host is supermicro server running windows 10 pro build 19044.1466. The ...
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tcp client which makes many outgoing connections

My TCP client need to connect to thousands servers (in local network) all at once. Communication is simple. 10 bytes string TCP request, 20 bytes response. I have gigabit network. when client connects ...
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Drop connections with a mismatching client certificate CN in nginx TCP reverse proxy

I'm using nginx to add TLS functionality on top of an existing TCP server (Redis) by proxying it like so (please read on before saying "Redis has builtin TLS support"): stream { server { ...
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TCP servers on macOS Catalina 10.15.7 not sending a SYN/ACK

I have a macOS laptop running Catalina (10.15.7), using the built-in WiFi interface. I have a Thinkpad laptop running Ubuntu 20.04, and a Windows 11 Desktop. I'm trying to access a webserver on my ...
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Traceroute - Header Link CURL result Issue

We have systematic CURLs run every 15 mins - 2 hours from this system and logging their status. Every other CURL for the past 2 months has succeeded except this. Is there a way to identify why this ...
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1 vote
1 answer
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Load balancing: how to find the fastest route to a user

I’m thinking about it like a week. Consider that we have a load balancer server, and two storage servers, X and Y. A user connects to load balancer. Load balancer should decide which of that two ...
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High cpu usage over TCP

I'm running haproxy 2.4 and when the haproxy is configured in tcp mode i get a high cpu usage. Example: Running the stress tool to generated arround 30k connections: ./pst -c 100000 -r 100000 -u ...
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TCP DUP ACK/Out-of-Order/Previous segment not captured/Retransmission flooded on wireshark logs

Due to slow network, I installed wireshark on the device(laptop) to find this This is a log of the device using internet(Downloading a file),as you can see at the right end of the screenshot, the ...
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How to improve TCP tolerance to out-of-order delivery in Linux balance-rr bonds and/or FreeBSD roundrobin laggs?

I have 3 servers networ kwise configured as follows A is a DELL R710 is running Linux 5.13.19-1-pve Proxmox VE 7.1 and has 4 NICs teamed in a balance-rr mode bond. B is a DELL R610 is running Linux 5....
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AWS ALB Handshake resumption

I have a problem where the AWS ALB TCP is initiated and every request which causes unnecessary latency of 0-150ms Example from postman to show what happens at every request. DNS lookup, TCP Handshake ...
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2 votes
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What may cause TCP / HTTP request's delay / lag

We have a device that sends POST requests or TCP messages in fixed intervals, with a JSON payload, through the internet to our server running a node application, on another location. The JSON payload ...
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Traceroute works but nc fails - Where is my port being blocked?

I am trying to troubleshoot two Azure VNETs that have been peered together. Lets call these VNETs A and B. There are multiple services running on a VM in VNET A on different ports. I am trying to ...
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GCP TCP Load balance IP at some countries are failed to connect, TCP 80 443 connected to this IP frequently timeout, any limit of TCP connections?

Hi we create GCP server and load balance at Singapore and Germany, at recently, both this two data centers Load Balance IP at some countries are failed to TCP connection, sometime are OK, but sometime ...
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rsyslog - Lower throughput when using omfwd with TCP vs UDP

TLDR; I'm getting significantly lower throughput when forwarding syslog messages with rsyslog on a Redhat server with 32 cores and 128Gi RAM to a remote server using TCP instead of UDP syslog in the ...
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TCP handshake not completing intermittently to specific Cloudflare node

I have setup a webpage with Cloudflare that works nearly all of the time, except occasionally the TCP handshake fails with the SYN+ACK not making it to Cloudflare. On a packet capture from another ...
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Clamav is very slow with tcp

I'm using clamonacc on my desktop computer and servers. I use a raspberry pi as clamd server. The clamd process only uses ~25% of all 4 cores so with htop I see it's using like ~100% and 400% is the ...
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syslog-ng / telegraf : EOF occurred when idle - incompatible?

This is a follow-on question from this previous question, created because I found out more information and it's cleaner to pose this as a new question. I'm using syslog-ng OSE v3.31.2 to receive ...
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syslog-ng: How to reduce high latency when forwarding logs to a syslog tcp consumer?

UPDATE 2: I've answered this via my new question at the link below. The root cause is behaviour by telegraf where by default it disconnects the TCP connection 5 seconds after the last received message....
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netcat no reaction to syn packet crafted with gopacket

I want to do some experiments with TCP packets. Therefore I am using the gopacket (v1.1.19) to craft packets and send them onto an interface. I have this code for creating a SYN packet and putting it ...
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Understanding TCP receive window [closed]

I'm currently learning about TCP, particularly the receive window aspect. I've read from several sources about it, and there's something I want to make sure I understand. From what I've learnt, the ...
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TCP window scaling "proxy" for connection to cloud environment

We have a hybrid cloud/on-prem infrastructure connected by dark fiber at 10Gbps. Our on-prem stuff is pretty legacy so many of the devices use fixed TCP window sizes. Using the bandwidth delay product,...
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2 votes
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load balancing over single NIC to overcome per-connection limit

I have a strange setup where the ISP provides a very fast connection (10 Gbps) but limits each connection to 50 Mbps. This is fine for multi-threaded applications where I can just boost the number of ...
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So many TCP packets to domain server from domain clients

I have Windows Server 2012 R2 which controls my LAN. Everything was working fine (Shared Folders, Folder Redirection and so on) for a two months. But suddenly, there occured delay on communication ...
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Kernel TCP tuning for buffer overrun and packet collapse

We have a Nginx+Ruby application where the data between Nginx and the application are interfaced through a socket. As part of performance improvement, when we analyzed the netstat statistics on the ...
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Strange TCP sequence from a device

I'm debugging strange connection reset problem in Java and got the next Wireshark capture: What can be the cause of repeating that ACK? I'm sure that the device received data correctly as it is ...
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How to make bind force clients to connect via TCP only?

I want to set up an experimental nameserver that asks clients to send requests via TCP only by sending back packets with the TC bit set. For that purpose I tried to work with the rate-limit parameter ...
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network issue with wsl2, nslookup works, but ping fails

I am facing bad network issue with networking on windows10 machines. tried most of the solutions available over internet. yet there is no solution. Solutions tried - Solutions related to enabling ...
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NGINX TCP Load Balancing is ip-sticky when it should be random, per request

I have an NGINX server being used as a TCP load balancer. It is default to round-robin load balancing, so my expectation is that for a given client IP, every time they hit the endpoint they will get ...
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2 votes
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Spikes on softirqs RCU monitored with NetData on proxmox container

I have a server with the following characteristics: https://www.soyoustart.com/it/offerte/1801sysgame05.xml Processor Intel i7-4790K RAM 32GB DDR3 1333MHz Traffic Unlimited Anti-DDoS Included Disks ...
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Too many RPC connections make web socket closed

Several servers are connected via RPC. There are times when apps in OS have too many RPC calls, which causes the network to become closed. What is the best way to debug or configure my OS? "msg&...
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3 votes
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AMD EPYC 7413 slow down to arround 400mhz when running iperf

we are trying to setup a 40gbit connection between two servers and get weird cpu behaviour when using iperf. It is also only using around 10Gbit/s of the possible 40. Server specs: AMD EPYC 7413 8x ...
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Port 80 not open. Still gets 404 when curl

Weird issue I'm facing currently! There is nothing running on port 80. Still curl gives 404 page not found. I can telnet to port 80 and even start a container exposing port 80 (host). But no requests ...
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tc traffic shaping with HTB and CQB causes packet transmission gap inconsistencies

Problem: When the tc HTB or CQB is used to do traffic shaping, first two packet that are sent after some time gap are sent back to back as recorded in the pcap log. I have a intermediate computer with ...
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Troubleshooting steps when the server not responding to some SYNs

What are the troubleshooting steps that I can take if I see that my Linux server does not respond to some of the SYNs that are being sent to it? (I know this from PCAPs that I recorded on my server) I ...
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