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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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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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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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Where are refused connections logged in Debian?

On my Debian 8 server, I want to check whether or not the server has refused any TCP connections. Is there any log (either already probably enabled by default, or that I can enable) where all incoming ...
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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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Pipelining data from one port to another on Linux [closed]

Is there a tool or a way to listen to one port and receive the data and to send the same data to another port. I need a tool witch does not have much overhead, preferably none, to measure a full round ...
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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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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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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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1answer
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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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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
55 views

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
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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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1answer
86 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
50 views

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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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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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 ...
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1answer
162 views

Connection Error with TCP sockets between a Windows 2012 R2 and Linux Centos7

I have a connection problem with TCP sockets between a Windows 2012 R2 machine and Linux CentOS7. When I run a perl client that sends several messages from Linux to a Windows perl service, it allways ...
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1answer
250 views

How to debug frequent “connection reset by peer”

Recently I started to have very frequent "connection reset by peer" on calls to an external provider. My application (client) is a Go application, doing some simple POST to an external provider over ...
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Support virtualhost routing without SNI support in the client

We are trying to build a TCP proxy that can forward to multiple virtual hosts. The idea is that a single IP address can be used to route inbound requests to multiple internal IP addresses. The initial ...
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1answer
26 views

Block outside TCP requests from centos server

I have a centOS server and user to host web systems with LAMP. Server owners are complaining that we are sending abnormal TCP requests to external server. How can we block these types of requests? ...
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1answer
47 views

Finding the value of `TIME_WAIT`

How does one determine the value of TIME_WAIT for port reuse? I am running a non-persistent HTTP load generator on a client box and need to find this value on the client. I see cat /proc/sys/net/ipv4/...
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Typical Bit Error Rates of TCP

I'm asked to simulate a TCP connection. To do so, the BER is said to need different seeds. So my idea is to let the BER be randomly distributed (for example truncnormal-distributed with a mean of 10^-...
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262 views

Windows Server 2016 Dropping Packet Retransmissions

We've come across an issue where we're able to narrow down root cause and hoping the collective here can provide insight. We have an AWS EC2 instance, c4.8xlarge, that is dropping tcp retransmits ...
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Improve single HTTP transfer bandwith over high latency connection (Ubuntu Linux)

I'm trying to improve the file transfer speed for my web server in Roubaix, France (hosted by OVH) over high distance/latency connections. I know that TCP connections are affected by higher latency, ...
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network ports are filtered strangely?

I have some Ubuntu servers deployed in VULTR Global Cloud and I have about 300 network ports each server. However, every server will be filtered in China suddenly (I can ping from China). I use nmap ...
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Monitor outgoing network usage per HTTP request

In Apache prefork server running PHP application on Linux, each HTTP request might fetch some data from other server, for instance Memcached. Let's say we want to find out top 10 HTTP requests (ex. ...
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2answers
318 views

Postfix protocol error attempting email address validation with SMTP

I have some code that does an email address validation. It works by attempting a mail delivery via SMTP and then quitting without sending anything. It works most of the time, but in some fringe cases ...