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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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Local web-server doesn't receive large HTTP requests [on hold]

I have web-server on my PC (nginx or apache, it doesn't matter). When someone sends HTTP request with summary length more than ~2800 chars, event tcpdump doesn't receive that request. I have SNR ...
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Running tcpdump starts ssh flood

I have runtime Linux running in a PLC. My development machine is running Ubuntu 14.04. The PLC and the development machine are connected through a five port switch. I ssh to PLC from my development ...
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Linux - Bound TCP connexion from remote host to localhost

I was wondering how to bounce the connexion from a remote host to my local tcp server (which is listening on port 5555). On windows, I hooked the program, first of all, I blacklist the remote ip's, ...
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Socket usage with Linux

I am wondering, does anyone know if there is a setting within linux that designates the max amount of time a socket is allowed open? I ask this because for whatever reason, no matter if there is data ...
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iptables block all traffic from a IP after TCP handshake completed

Other than writing a script that monitors the log file to see if a full TCP connection has been created to a certain port is it possible to create a rule using the recent table that will block all ...
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51 views

Connection refused for Java HTTP Server running on localhost

How would you investigate the following issue? On a specific server; any HTTP-Requests sent to a Java Server running on localhost fails with "Connection refused". (See the Java code here) In the ...
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How to use socat to a dynamic IP

I'm using socat to redirect TCP traffic to my home from a server. The problem is that my home changes IP every day. If I start socat with a url, it'll not update after some time, it'll just use the ...
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Can anyone explain what this packet capture log means?

I'm setting up a replacement network gateway and everything is working except I can't reach 1 address in 1 of the subnets... All other addresses in the subnet 192.168.251.0/24 are reachable except 192....
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Server does not respond to SYN [duplicate]

When I launch an FTP transfer from a client machine, it fails because it cannot connect to the server. With tcpdump I can see that the client sends a SYN to the server, and I can also see that the ...
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why linux assigns ephemeral ports out of its range

I have a server running mysql, ssh and other services. I want to see the range for ephemeral ports available for the OS running: cat /proc/sys/net/ipv4/ip_local_port_range which returns 32768 - ...
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lsof displays two connections from one port

I'm following lsof output for my process COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME AppName 79899 heximal 7u IPv4 0x6c18d5501d2e17c9 0t0 TCP 10.3.2.8:...
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some servers won't reply to SYN if client is on VPN

We have some ubuntu 18.04 servers (both physical and VMs) that will ignore pings and TCP connections coming from clients connected to our intranet via VPN. It is only fresh installs of 18.04 that are ...
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How to filter packets bigger than 80 bytes in ethernet bridge (RasPi Debian)?

I'm working with RasPi with configured a bridge between two Ethernet interfaces. More or less I followed this guide The bridge works fine. But now, I'm trying to filter tcp packets bigger than 80 ...
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How to debug IIS 8.5 TCP resets?

I have a Win 2012 R2 / IIS 8.5 server that has been running a handful of public-facing production websites for 2 years. Today, for about 6 hours, it started randomly dropping port 80 requests (but ...
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1answer
61 views

How to turn an ethernet port into a passive listener?

I want to capture ethernet packets with my raspberry pi's ethernet port. I know I could create an ethernet bridge between two ethernet ports on the raspberry and analyze the packets internally with ...
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42 views

Tcp/IP Latency on Ethernet peer to peer connection

I'm having 2 computers connected over the ethernet and communication with each other in a test setup. No for a round trip for a message to travel from computer A to B and back it takes about 12 ms for ...
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NGINX server not responding to new connections intermittently

I have a web server set up and it usually responds extremely fast (<100ms) and on repeated connections even with keepalive_timeout set to 0 has no issues connecting. However, occasionally on ...
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What is a TCP stream in a Nginx connection?

I'm working with Nginx and I'm searching what is a TCP stream. I haven't found relevant definition on the web, so please maybe someone has any answer to provide us ?
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For many different TCP hosts, how can I differentiate and route them from the same external IP?

I realize I may be asking the impossible here -- At the moment I use too many elastic IPs, and they cost money. Not only do they cost money...but in a disaster scenario, it takes time to reattach 25 -...
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Cisco ASA 5515 - huge amount of long running idle connections

I've got a Cisco ASA 5515 and it's come to my attention that the connections usage is quite high. Here's the result of running show resource usage summary Resource Current Peak ...
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What is the difference between net.core.netdev_max_backlog and net.ipv4.tcp_max_syn_backlog

Several docs on the net describe these options as following: net.core.netdev_max_backlog: Maximum number of packets, queued on the INPUT side, when the interface receives packets faster than ...
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1answer
23 views

Analyze Packet Loss Bursts

I need to analyze packet loss bursts in TCP streams. Given a number X a packet lost burst is when more then X consecutive packets got lost. So I have a pcap file and need to count how many bursts ...
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In Linux server - how to check if established TCP port connection supports TLS 1.2

I have a Linux server that has an established TCP port connection to a client. Can I somehow check if the connection on this port supports TLS 1.2 with any of the networking commands on a basic Linux ...
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Why a TCP connection fail faster on Linux closed ports than on Windows ones?

While trying the simple exploit described here I noticed that it doesn't works on Linux while it works on Windows (tried with several browsers). Apparently this is because, on Linux, the operating ...
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Is it possible for packets sent using TCP to ever arrive with different data? [closed]

Sometimes in my networking library when I send a packet the data arrives different than when I sent it. I assumed that TCP guarenteed exact delivery. Is this true? Or must there be something wrong in ...
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2answers
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iPhone OS 11_3 http connection flood

I have been trying to limit max TCP connections to port 80 of my server coming from the same IP. I have used iptables for this task: -A INPUT -p tcp --dport 80 -m conntrack --ctstate ESTABLISHED -m ...
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All TCP packets have the PSH flag set - who / what would be responsible for that?

On a server->client TCP stream, all packets from the server have the PSH flag set. Is good old Nagle responsible for this flag being set?
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“edit” TCP header in a incoming traffic

I have three set of servers which will involve for the current data flow. Server A ----> Server B ---> Remote Server/Storage I am downloading/push files from Server A to B, and then server B will ...
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reasons for fastpath sockets to fail?

I have a windows 2012 server that refuse to open TCP fastpath connections. The code that opens it do all the possible tests in every step on the road and it doesn't have any errors (it also works on ...
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1answer
76 views

Set static TCP port in SQL Server unattended installation

I have an unattended installation of SQL Server 2016 using the .INI answer file. In my answer file, I enable TCP like this: ; Specify 0 to disable or 1 to enable the TCP/IP protocol. TCPENABLED="1" ...
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Logstash losing connection to Elasticsearch nodes

We're running Logstash on a server which is pushing logs into an Elasticsearch cluster. In the Logstash logs we see it losing connection to the Elasticsearch servers with a connection reset error. We ...
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1answer
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Getting number of established TCP connections per unit time in Amazon Linux (CentOS-based)

I'm running a server in AWS on the Amazon Linux operating system (it's a variant of CentOS I've heard), and I'd like to count the number of TCP connections that get ESTABLISHED per unit time to a ...
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How to set up a persistent TCP gender-changer proxy?

I have a provider (A) that wants to send us data through an incoming TCP connection. Unfortunately the consuming service (B) cannot receive inbound TCP connections. Also it does not have a static IP, ...
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How to forward traffic over a single port via OpenVPN?

I've successfully setup an OpenVPN server on a VPS Debian distro and have been able to connect to it via from my Windows client. My situation is a little unusual in that I don't want to use the ...
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Remote Client is unable to connect to TCP Server on VPS (Getting 10060 error)

I have searched all over the internet for the solution. Unfortunately, I could not get any working solution yet. Here is the story. I am running TCP server for small communication application on the ...
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Nginx port refusing outside communication on Linux

I need to open port 82 for Nginx to route some CURL requests to Elasticsearch. Localhost requests are passing just fine when I do "curl localhost:82/" but from my machine it is being refused with "...
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What happens when UDP and TCP are sharing a link?

The question that I have is about TCP fairness: Say one Host ist transmitting data via UDP, while a second Host is transmitting data via TCP. Both of these Hosts use the same Ethernet connection. ...
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Packet Loss Analysis of a UDP upload in dependence of shared link capacity

I consider two hosts: Host1 is sending UDP packets (between 1000 and 1500 Bytes) to Host2 and at the same time Host2 is sending UDP packets (also between 1000 and 1500 Bytes) to Host1. The ...
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1answer
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Netstat output contains several connections with the same ip and port

Netstat output (netstat -an) contains several connections with the same foreign (client) ip and port, for example: TCP server_ip:49421 client_ip:4000 TIME_WAIT TCP server_ip:52772 ...
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1answer
157 views

SFTP slow with high latency

Server has a 1Gbps uplink speed, local PC has a download speed of 100Mbps. Latency is 89ms. SFTP speed while downloading a single file from the server to the PC maxes out at 2.5MB/s, even though ...
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142 views

Haproxy Passthrough SSL and http logs?

I am running a proxy service, thus I can only use TCP passthrough, or users would get certificate warnings. Unfortunately very little is known in tcp logs, and I want to ensure no illegal activities ...
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1answer
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tcpdump TCP Header offset 13

I am trying to understand how tcpdump works and trying to read TCP header control flags SYN,ACK etc. After researching online I came to know that the control flags are available at offset 13 and I ...
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Fixed route for a network interface with two IP aliases

On a Windows 2016 Server, I need to set a custom route, so that connections to a specific destination ip address always use a specific source ip. But while the route add command allows me to specify ...
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TCP Client-Server connection inside Docker

I have a GUI application running on my host (a CentOS 7 VM) at 127.0.0.1:3281. This connects to a server, also running locally at 127.0.0.1:1341 via a TCP channel. This works perfectly on my CentOS ...
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1answer
195 views

Very high tcp retransmit rate to Internet on devices inside LAN

I work with Linux systems a lot as a developer and have a moderate level of networking knowledge, but the following situation is a real baffling mystery: I'm running pfSense 2.4.3 (that's current) on ...
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How many concurrent TCP connections or sockets can be handled by a web server for e.g in a chat application

I find that all the chat servers either use sockets like WhatsApp or long polling to provide the to and fro flow of messages. I wonder how so many concurrent TCP connections or sockets are maintained ...
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1answer
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How can I count / view all fast-path sockets on windows server?

In case you're not familiar, fast path loopback sockets: https://blogs.technet.microsoft.com/wincat/2012/12/05/fast-tcp-loopback-performance-and-low-latency-with-windows-server-2012-tcp-loopback-fast-...
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1answer
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How do I access TCP connection? [closed]

I am extremely new with networking and am learning about the TCP Layer; I'm writing software thats going to speak with a tcp server. I tried googling: tcp schema and tcp protocol but i cannot find ...
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TCP delays after spike - receives 1460 bytes every two minutes

I am seeing a strange behavior with a TCP connection. I've a sender which sends data in spikes. After the spike, the receiver starts seeing 1460 bytes every two minutes, even though the sender has ...
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1answer
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Kubernetes (K8S): TCP clients waiting very long timeout on connection to a Service when there are no Pods serving its requests

My problem occured when using Redis on Kubernetes, but it seems that it is not a problem with Redis itself, but with network/infrastructure. My scenario: I have a Redis Service with single Redis Pod ...