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Questions tagged [tcp]

The Transport Control Protocol (TCP) is a low-level part of the protocol stack used by the Internet. It sits directly above the IP layer and is responsible for making sure that dropped packets are resent.

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reusing same port in a tcp application under different namespaces on linux VM

i have a linux VM with 2 interfaces, eth0 has mgmt IP and eth1 has configuration as below ip netns exec eng51 ifconfig eth1.51 Link encap:Ethernet HWaddr 52:54:00:bd:68:c3 inet addr:51.51....
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Can TCP kill be used to stop a foreign nmap scan?

Suppose I know that a certain ip on my local host (say 192.168.0.3) is performing an nmap scan (or executing a script) on me. Is it possible to stop the scan using tcpkill?
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How Can I Kill Sockets Related to Services on Localhost?

I am trying to close sockets related to my webserver so the client does not have to refresh the browser twice to connect to the new webserver. I have successfully written a bash script which can ...
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how to turn off tcp timestamps?

I tried to turn off the tcp timestamp but it didn't work. The step i performed are the following: $ sysctl -w net.ipv4.tcp_timestamps=0 $ sysctl -p $ sysctl net.ipv4.tcp_timestamps (=> to be sure ...
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port forwarding using mptcp

I installed mptcp on two systems mptcp installation I followed this site to install mptcp and its working perfectly I check this site also mptcp check both systems will work perfectly. I want to ...
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Has the filtering of all kinds of TCP attacks using iptables become obsolete as they get filtered elsewhere or something else?

Background I am on Debian 10 Buster. I started running a Tor relay on my home IP address. A dedicated full-fledged server is probably not the most energy efficient way, but I want to try it out. And ...
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Traffic Generation

I require to generate TCP flows of various sizes and need to generate them after varying intervals. I also need to modify DSCP value of each packet based on it's flow size. What possible tools can I ...
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45 views

Virtualized firewall on KVM

I have few vms (homelab) virtualized with KVM (CentOS7) and connected to my home network. Lately I tried to isolate them by putting them in separate network and I wanted to do so with virtualized ...
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How to send data from Raspberry pi to Remote SQL DB without installing mysql or mysql Client

Hi I am new to Linux environment I would like send some port checking data and a timestamp ( both saved as a variable) to my remote Mysql DB running on a linux Node machine . I don't want install sql ...
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132 views

Linux's Internet domain socket, transport protocols (TCP/UDP)'s socket and port

I have been bothered for a long while by some confusions among internet domain socket provided by Linux, transport protocols (TCP/UDP)'s socket and transport protocols (TCP/UDP)'s port. ...
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Why can I not kill a process in the same line I start it using fuser?

I have been trying to kill a process by looking at the listening port and nothing seems to be working. The code is as follows: (code to open port 8545) && fuser -k 8545/tcp I also tried with ...
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What do `<expire_time>` and `<retrans>` mean in the output of `ss -o`?

ss -o shows TCP timer in the following format: timer:(<timer_name>,<expire_time>,<retrans>) What do <expire_time> and <retrans> mean? I found <expire_time> ...
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Why 1 second RTO lower bound is missing in RFC 6298 Linux kernel implementation

I was going through the implementation of RFC 6298. Then i found a statement as follows. Whenever RTO is computed, if it is less than 1 second, then the RTO SHOULD be rounded up to 1 second. But ...
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117 views

Tcp TCPBacklogDrop and packets pruned from receive queue

I am analyzing two virtual machines in the same LAN, tcp packet loss problem, but the knowledge has been exhausted. platform CentOS Linux release 7.2.1511 (Core) 3.10.0-327.el7.x86_64 #1 SMP Thu Nov ...
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37 views

possible packet loss

I have a program running on my local machine that prints data to port 50000. In a terminal on my local machine I run nc to connect to and print the data on the port. However, when using nc in terminal ...
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350 views

Which Unix-like system really provides the /dev/tcp special file?

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash: If the operating system on which bash is running provides ...
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Using socat to make a secure tcp connection to an irc server

Recently, I got into irc, so I installed sic and started - obviously - chatting. But, it turns out that sic doesn't provide any security features like SSL or TCP so I in man sic, they told to use ...
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171 views

How to Disable Ping ( TCP ) in Linux all the time? [closed]

I want to disable ping response all the time. I use the following command for disable ICMP ping iptables -A INPUT -p icmp --icmp-type echo-request -j DROP what should I do for disable TCP ping ?
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What happens to a TCP connection when the network is abruptly terminated

Say a user space application has a TCP connection with some non local endpoint. At some point, network gets abruptly broken (i.e. connection deleted in network manager, unplug the wifi dongle, cut the ...
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167 views

Delay between TCP send and actual write to the NIC

While looking for solution to a problem in socket programming with python described here (In short the problem is: I want my message(~ 25 Bytes) sent by a client over a TCP socket to be dispatched(...
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2answers
64 views

port 1556 listening on tcp6 causing issues

on my RedHat 7, i noticed that network connection for Netbackup stopped working and i tried everything including rurning off my firewall and disabled SELINUX with no luck. the only thing i noticed ...
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lsof shows protocol: TCP

I ran sudo lsof -p $(pidof foo) and I got a lot of these. Does anyone know what these represent? I know they come from the process but there are no ports / IP addresses. COMMAND PID USER FD ...
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Understanding how MobaXterm keeps an ssh connection alive

I want to have a stable ssh connection to a server where I do things. That would last for days or weeks. In general, one can set TCP keepalive to more than 7200 seconds: Socket reset by peer ever 2 ...
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Locally forward tcp port bidirectional

I wonder how it is possible to locally forward a tcp port, bidirectional, i. e. all packets leaving the local machine on port 25 (this port of course is actually dynamically assigned) should be ...
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Restrict inbound access on localhost:TCP port

For reasons beyond my control, I have a binary that binds to TCP "localhost:$PORT". (Unix socket bindings would make this question moot). If I understand correctly, this means that although no ...
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Total socket count steadily increasing, tcp/udp sockets steady. Why?

I have a server (Ubuntu 16.04.5) running sockets.io and a few other things. This server is running about 5 or 6 different python apps and sockets.io. When the server reaches this level of ~6144 ...
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1answer
4k views

max no of tcp connections on a linux system

I know that /etc/security/limits.conf provides the persistent soft and hard limits for several values. However, in the relevant list there is no indication about imposed limits on: a) concurrent ...
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2answers
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Telnet - how to verify why a port is blocked?

We have linux machines with RedHat 6.5 operating system. When we try to telnet to localhost on port 8182, we get connection refused: service iptables status Firewall is not running telnet localhost ...
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1answer
72 views

How to close one side of a TCP connection leaving other side hanging open? (No FIN or RST sent)

I am trying to recreate a scenario where a Solaris client is connected to a Linux server via TCP socket, but the client side of the connection suddenly goes down without sending sending a FIN or RST ...
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1answer
161 views

Deployment of haproxy between devices and Syslog server

Below is the current architecture of Syslog-NG to avoid single point of failure. Currently devices send same syslog message to two syslog servers listening on UDP port 514. Each server stores the ...
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1answer
106 views

nc getting stuck unexpectedly

I expected this: nc -l localhost 7000 </dev/null & nc localhost 7000 </etc/profile and this nc -l localhost 7000 </etc/profile & nc localhost 7000 </dev/null to finish after ...
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Is is possible to disable TCP timestamping per-connection?

I am writing simple TCP/IP client (in python, later perhaps using ASIO or Qt) for an embedded system which rejects connections when the first SYN packet uses TCP timestamps. I can make it working by ...
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Load-balancing through multiple interfaces on the same server using Nginx

I'm testing proxy server with combination of Nginx TCP load balancing and SNI based HTTPS proxy. In my testing debian box I have following interfaces configured eth0 192.168.1.10 - proxy eth0:1 ...
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1answer
49 views

TCP variants under lsmod

I was reading about how TCP congestion variants are implemented in Linux. Each variant is implemented as a separate module. When I had read this question: Add TCP congestion control variant to Linux ...
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227 views

order of rules' processing in iptables chains [closed]

Isn't the order of processing the rules in iptables top to bottom? Given the following example; Chain DOCKER (2 references) target prot opt source destination RETURN ...
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1answer
685 views

How does MTR (run with TCP protocol) calculate the loss rate?

I thought TCP protocol itself will guarantee not to loose any bytes while connecting. About this viewpoint, please refer to https://stackoverflow.com/questions/23841896/will-tcp-connection-lose-...
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1answer
488 views

How to find the cause of TCP RST on Linux (Ubuntu Server)

In my mail server I'm getting high TCP reset send between working hours, as shown in this grafic: This is a capture of the server traffic filter by tcp-rst: When I run "netstat -i" I get this: ...
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2answers
223 views

Send TCP packet to the same source [closed]

I want to design a system which reduce travel time of packet what is happening in reality is I send a SYN bit from client side, this bit travel through router then to server and server reply SYN+ACK ...
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3answers
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Is it possible to spoof a successful TCP connection with iptables?

Typically with IP tables you would either drop or reject traffic. For TCP is there a way to have iptables instead send a syn back but forget the connection?
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Different behavior between kernel 4.8 and 4.10 when receives the SYN packet

I have two Linux servers. server A: 4.8 server B: 4.10 There is a socket running on each server and listen at port 9999 with concurrent request limit as 1. When all concurrent request threads of A ...
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1answer
243 views

How to change TCP congestion control algorithm on OpenBSD?

On FreeBSD, I can change the TCP congestion control algorithm via net.inet.tcp.cc.algorithm. On OpenBSD, there is no net.inet.tcp.cc.algorithm parameter. So, here is the question: How to change TCP ...
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1answer
487 views

Get IP address of socket used by process

given a process Id (that use sockets), I would like to get the IP on socket endpoints. e.g When new SSH session is created, the sshd demon fork process per session. I want to get the IP endpoints ...
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54 views

How to open up a tcp server compatible with tcpgoon

I have tcpgoon installed on one computer, provided that there is a direct VLAN connection, how do I create a TCP server on my second computer?
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1answer
38 views

How can I be sure that an application is running on same cpu/core that its TCP send flow is?

Let's suppose the following (very simplified egress tcp queuing) flow: -->[app (nginx)] -->[send_buffer(tcp_wmem)] -->(qdisc txqueuelen) -->[ring buffer(tx_rx)] -->(dma) -->[...
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1answer
353 views

connect to server with netcat and receive *multiple* files with one request/connection

Say I have an http or tcp server running, which serves tarballs (.tgz files). Is there some way I can receive files individually so I can do something like this: nc localhost 5000 | how can I read ...
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1answer
216 views

How do I make ppp reliable over lossy radio modems using pppd and tcp kernel settings on debian?

I am having a lot of trouble establishing a reliable ppp / tcpip link between two debian systems over radio modems. My hardware topology is a little complex. The system uses: Raspberry Pi 3B at ...
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2answers
989 views

How can I detect if telnet is running on a server?

I have a digital scope, with LAN connection. I'd like to check if telnet is running on the scope (the manual doesn't say so, but then the manual doesn't offer anything useful about the LAN port). I ...
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324 views

Send response based on netcat client request

I am trying to create a socket where the client receives a response based on their request, but I can not figure out how to achieve this on CentOS 7. Until now I have the socket opened on port 100 ...
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1answer
37 views

How can I run this tcp command in Ubuntu? [closed]

I want to run this command in Ubuntu: tcp 0 0 0.0.0.0:50010 0.0.0.0:* LISTEN <pid>/java but tcp is not recognized in Ubuntu. What could be an alternative for this?
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mtu 9000 issues only on tcp and not icmp possible?

I have a connection between two datacenters and rsync between them stalls often. I think it is related to the mtu 9000 (I actualy set it to 8900 because of some possible vlan use) I have the ...