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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socat does not honor sourceport option

I am trying to send a udp packet from a specific port: $ echo hello | socat - UDP-DATAGRAM:192.168.1.255:11111,broadcast,sourceport=22222 But a random port is used instead: # tcpdump -vvvv -ttttt -...
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Using UDP multicast in Linux, recvfrom() cannot get data

I have a task to get data from a sensor device. Through the Wireshark, I can capture information as below: wich send information from 10.13.1.113 to 224.0.2.2 (Multicast Address). Src Port 42402, Dst ...
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Does the correctness of MAC address matter in UDP?

Here is the thing, I used tcpdump and created a UDP-only pcap file from production environment. Then with the tool tcprewrite, I updated the UDP packets dst IP and MAC address as vm2, src IP as vm1 ...
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Blocking UDP port 140 from receiving packets from source port 8989 (active way to send signal to sender that is unreachable)

So my problem is that I want to block UPD port 140 from receiving packets from port 8989, but I want to block it actively, not just silently ignore it, but to send an active signal to the sender of ...
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TCPDUMP IP UNKNOWN

I am seeing this in the tcpdump output 21:32:51.580969 IP UNKNOWN.9998 > 255.255.255.255.9998: UDP, length 12 What does 'IP UNKNOWN' mean? Is something hiding the ip address? Thanks
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Is there a tool to count the latency of UDP datagrams in Linux?

Now I want to test the network performance between two Linux systems. The test scenario is as follows: one terminal sends UDP datagrams to the other terminal continuously at fixed intervals (the ...
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what does `IgnoredMulti` statistic for Udp in debian linux mean?

I have a Ubuntu machine that is receiving UDP packets by joining a multicast group, occasionally we are getting UDP packet drops. when I am trying to monitor using netstat -s I get the following ...
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UDP VPN deauthentication problems openvpn

I use a VPN connection to connect to the network by using openvpn, the problem I have is the following After spending some time using the connection with a server it disconnects, I have tried with ...
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What is exactly the timestamp measured by tcpdump?

We have a server that communicates over UDP with two clients (client1 and client2), via the same NIC through a switch. The server runs on debian 9 standard kernel (no real time patch). The system is ...
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How can I send a UDP packet from my Linux ASUS router?

I have changed the firmware on my router, unanme -a yields: Linux RT-AC86U-8458 4.1.27 #2 SMP PREEMPT Fri Aug 6 18:32:35 EDT 2021 aarch64 ASUSWRT-Merlin I have logged in to ssh to this router, and I ...
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NFS client won't list files when using UDP

I have an NFS server (server1) that works fine with TCP, but when a client mounts it with UDP, while the mount point works, it can only list folder with no files in it. If there's a file in that ...
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How to get open connections statistics without ss or netstat

The question may sound silly but I'm trying to make a tool that uses ss data. Sadly I'm having some troubles regarding output format parsing (too much randomness depending on version and system). So, ...
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netcat blank result for UDP packets, with windows as listener and Linux machine as sender

I set one of my Linux machine as server , and ensure one of my windows machine as reachable from Linux. netcat was installed in both , while Linux is sending UDP packets , I am not able to capture any ...
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How to drop all unnecessary UDP traffic on INPUT chain?

About 2 weeks ago, I started running a Tor relay, which itself operates solely on TCP. So, I would like to drop all UDP packets, which are unneeded. But I don't know, what is actually needed (if ...
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tcpdump, determine transport protocol

Is there a easy way to determine the transport protocol of a packet by looking at the output of a TCP dump trace? I'd just like to be able to tell if a packet is UDP or TCP. I've tried using the -x ...
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Low-level tcp/udp proxy

Is it possible to set up a server which acts as a proxy that is able to delegate all incoming traffic (regardless of protocol) to the original destination? What I am trying to do is to allow only a ...
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Iptables Accept All From Specific Ip And Port

I want to accept all traffic that is coming from an IP address and its specific port to any of my ports. Here is the configuration: Details: I am using Jitsi in a server, and I want to reach Jitsi ...
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How to setup veth with 9000 MTU to simulate sending and receiving large UDP multicast packets on the same host?

The sender needs to transmit large data packets to the receiver (which is on the same host with 1500 MTU) and I think this can be simulated using veth with 9000 MTU, from my reading on it. But I'm not ...
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Only Flatpak apps can open all websites after connecting to VPN

I'm using PureVPN app (openvpn/udp). Installed via rpm file. After connecting, If I ping youtbue.com it shows: --- youtube.com ping statistics --- 7 packets transmitted, 0 received, 100% packet loss, ...
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reordered and duplicated packets when using UDP over loopback interface

We are seeing UDP packets being reordered and duplicated when being sent over lo. We can see this because we're sending MPEG transport streams, which have their own sequence number in their headers, ...
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linux bridge interrupts udp packet flow

I am having a UDP issue with the following bridging setup (Linux 5.11.6): (let ns${i} denote namespaces and left${i}/right${i} be veth pairs) ns1{right1(x.x.x.1)---}---ns2{---left1::bridge(x.x.x.2)::...
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Script that performs an action based on the contents of a UDP packet?

I'm trying to write a script that listens for broadcasted UDP packets on port 2088, read the data, and then POST to an URL. Specifically, I'm trying to make a LIFX light turn red when I'm on the ...
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Netcat listener: Line break between syslog messages

I am playing with netcat command. On this linux system, I have set up a netcat listener on UDP 514, so that I get to see syslog messages from remote systems. $ sudo nc -v -ulp 514 listening on [::]:...
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Any way to block UDP for a specific applcation

Is there any way on Linux to block UDP traffic for a specific process. I tried using AppArmor deny of certain traffic, but it only supports total denial of all network access, not a specific protocol. ...
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How to convert stream data which come over udp to video device?

I'm trying to share my computer's camera with the remote computer. In order to do this, I wanted to share my own computer's camera with the udp port(stream), take the stream on the remote computer and ...
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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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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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3 votes
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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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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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