Questions tagged [udp]

User Datagram Protocol (UDP) is defined to make available a datagram mode of packet-switched computer communication in the environment of an interconnected set of computer networks. This protocol assumes that the Internet Protocol (IP) is used as the underlying protocol.

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How to measure the duration of packet from network to process

I want to measure the duration of a TCP/UDP packet from network to process. Let's say that I develop a Linux process, which provides a kind of web service. My process is listening on the port 8999 and ...
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Using nftable to duplicate udp packet

I am trying to setup udp packet duplication. Usecase will be syslog messages. These messages are beeing sent to machine A ( xxx.xxx.xxx.177 : 5140 , debian 10). They are received by a service. With ...
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incoming UDP multicast stream stops after fixed time on macOS

My ISP provides IPTV feature, stream example: udp://@239.255.2.97:5500. I'd like to watch IPTV on macOS, so I used VLC. Initially, IPTV didn't work at all. At first I thought that it's locked to ISP's ...
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Linux: UDP “multiplexer” inside kernel

I have an application with very high performance requirements and the following job: There is incoming UDP traffic on port 1234. The packets have as fast as possible to be sent to hosts H1, H2, ... Hn ...
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Sending multiple packets of hex data with UDP

I'm trying to reverse engineer a wifi webcam that connects to an Android app. I sniffed the traffic and found that the transaction is initiated when the app sends a series of 8 UDP packets, at which ...
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state of tcp/udp source ports when waiting for answer from target

i have a quick question about tcp port states: suppose i am establishing a tcp connection to a server: source address/port should be 44.44.44.44:33456 destination address/port is 55:55:55.55:443. in ...
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396 views

Socat: send a UDP broadcast from stdin, but handling responses with SYSTEM

I'm trying to implement a simple proprietary discovery protocol using socat. The discovery is done by sending a UDP broadcast to a well-defined port with a small payload, then listening to "...
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UDP Packet drops

I understand that the receive flow for a UDP packet is Check udp header for errors Match destination to socket Send an error message back if no such socket Put packet into appropriate socket receive ...
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Why is it that TCP packets can be modified to block invalid packets, but not UDP packets

On a random day I was googling iptables rules to harden my desktop, and came across this post[1]. At some point the guide mentions blocking invalid TCP packets using tcp-modules with these rules; ...
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Bridge / Tunnel using netcat and named pipes

I have two devices (A and B) that should communicate with each other - indirectly via a server (S): /---\ /---\ /---\ | A | <===> | S | <===> | B | \---/ \---/ \---/...
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Why did iperf3 show thunderbolt speed 3 Gbit in one direction, and just 500 Mbit in the other direction?

I connected two MBPs via thunderbolt, via thunderbolt bridge which should provide 10Gbit/s bidirectional connection on one of its channels. I have them connected over a thunderbolt 2 male male cable ...
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Receive data on a udp port and forward the same on a tcp port

I'm not sure whether this is even possible, but I want to receive some data over UDP port (say 14550) and forward it to a newly opened TCP port (say 50000). I have tried socat as of now but no success:...
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What happens to data on unpolled datagram sockets?

I've tried to google this, but can't find anything. If I have a long running program that listens to a datagram (UDP) socket. If data is sent to my socket, but my program does not poll for it or read ...
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How to monitor a UDP specific port/socket?

I have an application that receives UDP packets at port 5000. In order to be 100% sure that the application is receiving all packets (for example the RX buffer could be full and some packets could be ...
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How does multicast routing work on the internet?

For a LAN, it is effectively several additional layers of filters on hardware/software, maybe including switch(IGMP snooping)/NIC/kernel stack, etc. Otherwise it is similar to broadcast. I think I can ...
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Can UDP multicast listening socket receive unicast packet, OR, can UDP unicast socket receive multicast packet, on Linux IPv4 stack?

My understanding is this, if a socket does not bind local address(or binds to INADDR_ANY), and does not call connect() to set remote address/port, then there is no way to prevent unicast packets to be ...
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Counting bytes on all connections traversing a Linux router

I have a Linux box which works as a router. How can I measure which connections send and receive how much data? For each hour, I would like something like: src_addr src_port dst_addr ...
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dmesg + UDP: bad checksum. + rhel 7.x

from the dmesg we get very strange lines as [6484420.812643] raid6: using avx2x2 recovery algorithm [6484420.859086] Btrfs loaded [6484426.278636] nr_pdflush_threads exported in /proc is scheduled ...
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Is UDP data lost when executing kill -HUP on rsyslog?

I am very new to rsyslog and I am going through the documentation as well as seeing examples of what other people have done with their configuration and a question came to mind when the topic of log ...
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Adding UDP checksum in IP layer after Xfrm transformation

I am doing a custom transformation of the packet using xfrm tables (IPv6). As part of the transformation, I am adding a UDP header (basically putting my data into an UDP a.k.a UDP encapsulation). The ...
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UDP multicast between FreeBSD QEMU guest and Ubuntu host

I am trying to perform UDP multicast between a FreeBSD QEMU guest and an Ubuntu host (this is part of an effort to use ROS2 on a FreeBSD-based research system). As a basic test, I've been running the ...
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Tunnelling IP Multicast traffic between two residential networks or machines

The Ableton Link music synchronization service operates by broadcasting and receiving messages via an IPv4 multicast group in the "Ad-Hoc 2" address block. In order to use the protocol to synchronize ...
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How to enable Nginx binding to UDP port 10000 with SELinux

Not sure if ServerFault is a better place for this question? I'm building a new application which needs Nginx to bind to UDP port 10000. If this were a TCP port for HTTP/S then I'd just add it to the ...
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Linux Kernel Holding Packet?

I've been looking at a 3rd party program for DNS resolution (on an embedded solution) and in the code to send the DNS query to the upstream server it will connect() then send(). send() returns with ...
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Outgoing packets from linux: Packets seen in tcpdump but not on destination

I observed that UDP packets are sent by using tcpdump; also, the sending process didn't cause any error when sendto() was called. However, on the destination host (which is within the same subnet) the ...
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ncat stops listening after 100 UDP packets

I'm continuously sending packets to a UDP server after 1 second. To listen for UDP packets: ncat -klup 1234 --sh-exec "cat > /proc/$$/fd/1" However, after printing 100 packets, nothing else ...
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Debian ignores second multicast packet

I have a home local network with several devices. One of the devices is sending multicast packets with information about some events (smart home). It works well - I've tried to launch Multicast Tester ...
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Is there a way in linux to increase the MTU size of a Broadcast interface on linux to be able to send bigger UDP packets?

I am broadcasting UDP packets on a Bcast:192.168.1.255 of a wlan0 interface on linux. Its working well and I am receiving an UDP client written on another machine. I learnt that I cannot send a UDP ...
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Ip address is of 32 bit, which means 4 bytes. Yet all answers to question on 13 root dns servers say otherwise [closed]

All of the articles I read that explains why there are 13 root dns servers saying each ip address takes 32 bytes and hence (13 x 32) = 416 bytes leaving up to 96 bytes for other protocol information. ...
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netcat -s switch does not work or do anything at all

I have a computer with a NIC with two ports and a switch between them, and I'm trying to send data from one port to the other using netcat. I thought I could simply specify the source address (i.e. ...
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Setting up UDP packets to two different destinations using iptables and PREROUTING

I am trying to send a UDP on a packet to two different external/remote IPs using iptables. Currently I am running a command that looks like this: iptables -t nat -A PREROUTING -i eth0 -p udp --dport ...
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/dev/tcp/host/port, /dev/udp/host/port what kernel module is this?

I noticed this in the bash(1) man page. Is there an operating system or certain kernel module that provides this interface? Tried it on my Debian installation and these devices do not exist. ...
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IPTABLES does not drop incoming DNS packets

I got an Ubuntu 19.10 VPS server which is serving some users for a certain monitoring traffic. Users connect, read a file and disconnect. Recently I noticed the aforementioned server is being used in ...
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iptables: Wrong destination-IP of duplicated UDP packet

I have the following setup: A data source (IP 192.168.178.1) sends UDP packets to a server. Server (Debian) collects and processes UDP data (IP 192.168.178.10, port 4000) PC (Windows 10) is supposed ...
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How to use a SOCKS5 Proxy in Unix

I have a python bot which works on UDP Protocol. I know that only SOCKS5 Proxies support UDP, but how do I use them? I have seen many tutorials but they're using ssh to connect to remote and that's ...
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UDP port forwarding with iptables in OpenVPN server

How to forwards all the UDP ports? I setup an OpenVPN server on my debian VPS & by using iptables, I forwarded all the TCP ports except 1100 & 1200. Here is the command that I used: iptables -...
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What encapsulation does /dev/udp use by default? Can I change it?

I am using /dev/udp to send a udp packet. For example, (taken from this answer) echo -n "This is a test" >/dev/udp/localhost/8000 I opened it up in wireshark to see what kind of packet ...
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UDP send buffer error in netstat

I we are running voice application which stream UDP (RTP) packets for voice, I am investigation some strange issue where my ifconfig ens4 | grep error counter going up specifically overrun If you see ...
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How to scan my computer's UDP ports

What command can I use to port scan UDP? I hear that UDP scanning has some specific issues, that do not apply to TCP scanning. I tried running sudo nmap -p0-65535 -sU 192.168.1.97. But it has been ...
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Port forwarding in Linux for UDP doesn't work

I'm trying to apply a port forward rule to forward UDP traffic from my AP on port 53 to a custom DNS server listening to 9053. I tried various calls. None of them worked. I've tried this in Kali. ...
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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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Redirecting UDP to local port the reply packet isn't SNATed, w/ iptables

I ran dnscrypt-proxy or tor on Linux listning on [::]:1053 to server DNS. I wanted to make all my Linux host's DNS queries transparently use that proxy. This is what I found from Internet how we ...
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How do I create a UDP packet?

When I perform the following Netcat command and view the packets with Wireshark, it says the UDP packet is malformed. $ echo "this is a test" | nc -u 127.0.0.1 53 Similarly, using commands like $ ...
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Retrieving the SO_INCOMING_CPU of a UDP Socket?

The socket API provides an SO_INCOMING_CPU option, the details of which are provided in the man page: SO_INCOMING_CPU (gettable since Linux 3.19, settable since Linux 4.4) Sets or gets ...
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Netcat: UDP connections don't terminate?

A simple example, here's my server/host: nc -ul 192.168.0.2 54 And the client: echo "test" | nc -u 192.168.0.2 54 The server will intercept the "test" message, but nc doesn't close. It just ...
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why /proc/net/udp is showing wrong rx_queue size in CentOS server?

I have a java server application. while(true) { serverSocket.receive(receivePacket); process(receivePacket); serverSocket.send(sendPacket); try { ...
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bridge between UDP and serial doesn't work

I've created a bridge between UDP and serial port using socat. Here is what I have socat -xv udp4:localhost:54321 open:/dev/ttyUSB1,rawer,lockfile=/tmp/s1.locak,echo=1,b115200,crnl To monitor ...
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create a UDP to serial bridge with socat

I have a piece of software that transmits data over a UDP connection. However in our system we can transmit data only over a serial port. I was thinking of making a bridge between a UDP and serial ...
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What UDP destination port(s) does mtr -u use?

traceroute sends UDP packets to port 33434 (and up) by default. I assume mtr -u (manual, homepage, github) does the same, but I can't find any documentation or test results to verify the destination ...
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UDP reverse proxy

Is there any easy way of doing userspace UDP reverse proxying? Specifically, I want the equivalent of ssh -R 10000:localhost:10000 $server but for UDP. I want this approach to be unreliable in the ...