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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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How can I have multiple TCP clients connected to server ttyS0?

I'm trying to test following envirorment: One server (it's a router, It has busybox and few other cmd) with a a physical serial port and and open socket #tcpsvd -v 0.0.0.0 -p 999 cat /dev/ttyS0 ...
Carmine Esposito's user avatar
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How to Log Each Outbound TCP Connection

At my company we have a set of 3 identical VMs. These VMs house an app that "sends messages". The app sends each message by making a TCP connection out to one of two fixed IP addresses (...
godot's user avatar
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TCP RST doesn't reach process running inside Podman container

I'm debugging an issue I'm seeing where connections between a podman container and the host aren't being closed inside the container. I've written very simple test programmes: server and client. ...
jezza's user avatar
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Why receiving TCP network packets require more memory bandwidth and CPU utilization than transmitting packets?

I am analyzing an ARM system with Linux kernel 5.15 running. I am running iperf3 to measure the network throughput between two ARM systems. Note that these are simulated systems and are loosely ...
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TCP out-of-order and GRO feature with linux kernel 5.14

according to the RFC9293, the PSH flag will be set in the last TCP segment created from the buffer (Ref. https://datatracker.ietf.org/doc/html/rfc9293#name-send). I'm in a scenario where the traffic ...
Mr Wolf's user avatar
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stdin redirection from /dev/tcp/localhost/port

I'm trying to get my head around some TCP-related topics, and have been experimenting: The following works fine: Process A: nc -l 12345 | wc -c Process B: </dev/random head -c 1k > /dev/tcp/...
k314159's user avatar
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ARM-LINUX-GCC with LIBMODBUS

Hi everyone, I'm trying to compile a program using "arm-linux-gcc" with "libmodbus"; however it seems the compiler is not set up for libmodbus. What should I do to fix it?
Tráng Đặng Đình's user avatar
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How to protect a docker container with tcp wrappers, xinetd or something like that?

I have a Dicom medical docker container, on a bridged network, that receives tcp connections (not web/http/https) from other Dicom enabled devices, such as MRI scanners. It is an old DCMTK binary ...
Dolapevich's user avatar
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Linux reuse of ports after TCP RST

I have a set up where I do a lot of HTTPS connections to customers, and under high load some connections time out. After digging a bit I found that it happens when we or the server (same behavior in ...
Zmegolaz's user avatar
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Prevent port scanning on OpenWRT

Imagine you need to have open ports on your Internet router but you don't want them to be easily discovered or enumerated. How can you prevent hackers/companies from scanning your open ports?
Artem S. Tashkinov's user avatar
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Ubuntu server, packets from outside network not reaching local socket but seen on tcpdump

I am running Ubuntu server 22.04, and have a peculiar port forwarding issue with a local machine. This machine has two Ethernet interfaces and the connected enp1s0 interface has an IP address 192.168....
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How to see all tcp ports listened on locally

I have a WSL2 instance with Ubuntu 22.04. I have installed microk8s and enabled the local registry. The local Registry in microk8s listens on node port 32000. I can access this registry in WSL on both ...
maloo's user avatar
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2 answers
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Does Linux TCP stack processing happen before or after netfilter?

The Linux netfilter has multiple hooks at different OSI model layers according to this image. However, the transportation layer protocols like TCP requires additional processing like retransmission ...
William's user avatar
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Log PID and TCP Listen

I'm trying find, how can I log all process activites, for logging all TCP Listen syscalls. System is linux. My main problem, I need do some logging for passive FTP connections, but with time occurence,...
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How to measure TCP latency?

OS is Debian on both servers. I found some examples showing how to measure TCP latency with nmap: nmap --packet-trace -p 22 192.168.0.10 But I'm getting some negative results for latency. ie, it will ...
cat pants's user avatar
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What is header-data split and why it's needed for TCP_ZEROCOPY_RECEIVE page alignment?

I'm currently investigating about TCP_ZEROCOPY_RECEIVE and I read that it requires header-data split support of NIC. As far as I understand, this feature is to DMA the header (IP, TCP headers) and ...
Sangyeop Lee's user avatar
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How to force TCP window scaling using SSH?

Inter continent data transfer's speed is maximum 2MB/s. I checked and the SSH server of my server doesn't even use window scaling, and the window itself is very small, around 22KB... Flags [S], seq ...
None's user avatar
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What's the differnce between "Connection timed out" v/s "No route to host" for ncat command?

I tried to use ncat command to 2 diff unknown IPs from a CENTOS 7 (linux) terminal. [abc@localhost ~]$ ncat -zv 10.11.78.5 22 Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: No route to host. [abc@...
Ayush Raj's user avatar
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Script to execute a task when certain TCP traffic appears (Raspberry Pi OS Bookworm)

I am using a Raspberry Pi as a Wifi bridge in my kitchen at home to bring network connectivity to a device that only has ethernet. I used a Will Haley guide and it works great. That part is solved ...
Naylor's user avatar
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Do bind mounts from NFS path create additional connections to the underlying NFS server?

I am designing the following setup: NFSv3 server Centos7 Client The client mounts an NFS share from the server to /mnt/nfs_share Now I want to create many read only bind mounts from that mount to ...
user48240's user avatar
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4 answers
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Ist it possible to check the peer address before accepting a TCP connection?

I wrote a simple Perl server that listens on a TCP port/socket, accepting connections. Now I wonder: When wanting to implement address-based access control, is it possible to check the address of the ...
U. Windl's user avatar
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sysctl prameters seem not working on a VM

I am trying to tune my servers performance. To do so, I wanted to test some sysctl prameters such as net.core.somaxconn, net.ipv4.tcp_max_syn_backlog and net.core.netdev_max_backlog. Following were my ...
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TCP/IP Network in Ubuntu 22.04 Becomes Unresponsive After Heavy Network Load from MPI Program

I have two identical servers running Ubuntu 22.04.3 LTS. Both systems have 2x AMD 9654 CPUs with 192 total cores and 512 GB of RAM. Each server has two 10G ethernet ports built into the motherboard. ...
Michael S. Emanuel's user avatar
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simulate differente Src IP (spoofing) for testing geoip filtering

I would like to simulate different ips for testing traffic filtering according to the ip origin. I did some tests using iptables and 2 containers simulating node1 and node2 using a bridge network. ...
creatldd1 creatldd1's user avatar
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Anyone know of a TCP-based tunnel protocol linux will support?

I have a lossy (1%) 10gig link between geographic locations which supports legacy systems that have non-tuneable TCP stacks. They have horrible throughput across the link because their TCP stacks ...
Colo Host's user avatar
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Question on encrypted DNS over Quic? How is it encrypted?

Suppose,I am using DNS over Quic. Since it is an encrypted protocol as it claims. My question is if intermediate servers cannot see my dns query, how will my dns query be resolved? It says that the ...
Mikey's user avatar
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Established but hidden TCP connection

On computer 10.196.111.161, I can see the following established tcp connection: [10.196.111.161]# netstat -natp | grep 7000 Proto Recv-Q Send-Q Local Address Foreign Address State ...
meolic's user avatar
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socat et al.: run a command when incoming connection is received

Let's say one is listening on a tcp port for an incoming connection using socat like this: $ socat file:`tty`,echo=1 "TCP-L:8080" Is is possible to run a command (just once) when connection ...
codepoet's user avatar
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Why does netstat show my socket tutorial program having a port of "x11-1" instead of the port I set in code?

I am trying to learn about socket programming, and I have the following function to set up a socket: 29 int CreatePassiveSock(char *protocol, char *portstr, int qlen) { 30 ...
Anthony De Vellis's user avatar
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conditional flush tcp sockets on linux

whenever I write data to a tcp socket, it waits until its filled with enough data ex: 64k (max packet size) then it sends data to the wire. this misses the data at the right time for the other end. ...
user3840019's user avatar
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How can I redirect traffic for a specific user to connect to another server?

what I intend to do is transfer the traffic of just a specific user to another server (IP). with the commands below it will work very well to transfer only the traffic from the entire server, which ...
Luana's user avatar
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Linux socket modes of IO

There are three modes of i/o. They are Programmed IO, Interrupt IO and DMA. My understanding is, Programmed IO requires CPU to busy-wait while Interrupt IO by nature, is ansynchronous. Where can I ...
cpp's user avatar
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TCP Congestion Window in Linux

I'm making some test between two peer (CentOS7) in a 10Gbit network with iperf. The configuration in /proc/sys/net/ipv4 and /proc/sys/net/core are exactly the same, so every socket buffer default size ...
Andrea Montanari's user avatar
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How to clean TCP Established state sockets?

I'm experiencing an issue with my rented VDS server, which is running Ubuntu 22.04. To secure my server, I have enabled ufw (Uncomplicated Firewall) and allowed access only to two TCP ports: 2222 for ...
Mehmet Fide's user avatar
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Problem with connection between custom application and qpidd compiled on ArchLinux while running them on Debian

I have a custom application and qpidd (Qpid version 1.36) which had been built on ArchLinux. Default TCP with default settings is used as protocol to connect to the running qpidd, and the connection ...
Viktoriia Pashchenko's user avatar
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Problem using Iptables for filtering traffic on a network interface which is a bridge port, on a specific tcp port

I am using iptables as firewall to filter traffic. I want to block traffic on a network interface on a certain tcp port (I'm testing on port 22). The network interface is a bridge port, so I'm using ...
foadk's user avatar
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TCP connect() call to device on local network very slow

I am running a local DHCP server using isc-dhcp-server on Debian linux, address 10.0.0.1. I have a relay on 10.0.0.99, to which a pulse is sent every 4 seconds or so via an HTTP request. The pseudo-...
Cheetaiean's user avatar
1 vote
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396 views

TCP/IP client-server slow communication

I made some network application. It is a client-server solution using the TCP/IP protocol. Clients connect to the server. They make several connections every second. Communication consists of units of ...
DaBler's user avatar
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prometheus node exporter sockstat

I'm looking for the meaning of the node_sockstat_TCP_mem_* metrics. The output of the node exporter describes them as follows: # HELP node_sockstat_TCP_mem Number of TCP sockets in state mem. # TYPE ...
Emmanuel's user avatar
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How does sshuttle actually forward TCP packets? How is it different from a full-fledged VPN?

Here is the scenario: On myHost (1.1.1.1) I run: sshuttle -r user@remoteHost 0/0 Now, if I check the my current IP on myHost with an http request directed to one of those services that echo your IP, ...
floatingpurr's user avatar
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TCP port visible from inside nor outside

I've used autossh (reverse) connecting to my server. The ssh side works like used to. But in an ARM64 system, my Ubuntu has less possibilities but this is another story (...). So what I see whit nmap ...
Erkman's user avatar
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Unable to send more than 60 bytes TCP packets using traceroute or tcptraceroute

[root@host33cn ~]# traceroute -M tcp -f 255 -m 255 -q 10 -w 1 -p 9101 10.11.1.6 1400 traceroute to 10.11.1.6 (10.11.1.6), 255 hops max, 60 byte packets 255 host05cn.zen.com (10.11.1.6) 0.112 ms 0....
veeranjaneya reddy's user avatar
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How to build kernel after modifying specific files?

I'm new in kernel development and I modified two kernel files for a research project. Now, I already know how to do a fresh building of the kernel source code and that is what I did. I'm asking if I ...
Lorenzo Pappone's user avatar
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1 answer
484 views

NFS client (ubuntu) froze after a while with openbsd server / FIN_WAIT_2

I have an openbsd server sharing directories through NFS protocol. After I installed a new version of ubuntu on the client, I still mount NFS directories however after a (random) time: nautilus, ls ...
Airwan's user avatar
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why is proxied TCP traffic much faster than routed/VPNed TCP traffic

I have a VPS which can download a file from Server X at 2gbps. I have a home internet connection which can download a file from the VPS at 1gbps, but from Server X at only 100mbps. If I use a SOCKS ...
Mir's user avatar
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Applying patch file to ubuntu server

Can someone please explain how to apply a patch file to ubuntu server kernel? I'm trying to apply this patch file which enables the tcp_collapse_max_bytes option in the TCP communication options on an ...
Erfan's user avatar
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Unable to read data from gpsfake

I saved the following NMEA-messages to the file messages.txt: $GPRMC,131131.00,A,5956.4298,N,03015.4464,E,00.00,310.5,130123,,,D*53 $GPRMC,131132.00,A,5956.4298,N,03015.4464,E,00.01,097.3,130123,,,D*...
ka3ak's user avatar
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command that shows all online connections?

I used TCPView to see all TCP and UDP endpoints in Windows. Is there any linux command/gui that has similar functionality?
ant4598's user avatar
1 vote
1 answer
411 views

What type of queue is TCP accept queue in Linux -- FIFO/LIFO/other?

I am wondering if TCP accept queue in Linux is a FIFO or LIFO, or any other type of queue? Asking the same from another perspective: does accept() yield connections in the same order as they arrived ...
Kuchara's user avatar
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What's the default KeepAlive value for a TCP socket in a UNIX-like Docker container?

I am creating a TCP socket as follows: _socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); if (Environment.OSVersion....
Dominique's user avatar
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