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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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I'm trying to ssh to a remote server. But after the ssh is successful the connection freezes within 2-3 minutes and eventually drops. On checking packet trace i observed my mac is randomly sending a ...
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Consider the topology where 2 QEMU VMs running Linux Ubuntu 16.04 kernel version 4.4.0-210 have both virtio-net interfaces with TAP backends connected to the same (host) Linux bridge and an SSH ...
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I've come across the following DTrace one-liner on https://wiki.freebsd.org/DTrace/One-Liners: # Summarize TCP life span in seconds: dtrace -n 'fbt::tcp_close:entry { @["TCP life span (...
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So basically i installed an Automation Anywhere product in Amazon Linux 2, when i checked the netstat -tulnp | grep LISTEN i didn't found the Listener that's supposed to be there exist. Thus leading ...
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I've measured ss --tcp --numeric --no-header --kill dst 1.2.3.0/24 on various machines (all running Ubuntu Server 22 or 24 LTS) and it consistently needs around 7-10ms to complete. Any idea where the ...
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I have a ARM Cortex-A9 dual-core processor running with 800MHz. An yocto based embedded Linux with kernel 5.15 (will be updated to 6.6 soon) is executed on the ARM processor. When I transfer data ...
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In my InfoSec course assignment, we were given the task to analyze the different communications that were displayed when we run the command netstat -an. While analyzing I saw the following ...
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I can't find any documentation that would explain the syntax and evaluation of the following sample constructs: add rule filter output tcp flags & (syn | ack) == syn | ack add rule filter output ...
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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 ...
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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 (...
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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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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 ...
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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/...
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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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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 ...
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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?
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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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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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@...
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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 ...
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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 ...
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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 ...
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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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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. ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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-...
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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 ...
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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 ...
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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, ...
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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 ...
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[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....
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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 ...
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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 ...
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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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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 ...
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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*...
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