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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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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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Process in Android making UDP connection not registered anywhere

Google gms is listening on a port using UDP protocol but /proc/net/udp does not display the socket neither /proc/pid/fd displays any socket with inode(only anonpipes) anyone knows why this happens? If ...
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how to ping (multicast) between two Gnu/Linux PCs

Firstly, I don't have much idea about multicast in Gnu/Linux. Is there anyway to assign fixed multicast IP address on both PCs (E.g. fixing unicast IP address in PC), and how to enable multicast in ...
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Losing syslog packets between hosts

I am losing syslog packets between two redhat servers. They are both virtual machines and have a couple of virtual firewalls inbetween them. I have no access to the firewalls but am assured that the ...
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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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1answer
44 views

How to scan my computer's UDP ports

I have tried running nmap 192.168.0.97 to port-scan my computer, and I noticed it only lists TCP ports. For both TCP and UDP ports, I would start by asking the OS on my computer. I.e. How do I list ...
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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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195 views

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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1answer
3k views

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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773 views

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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191 views

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 ...
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432 views

ncat v7.6 UDP -k and -w not working as expected

At work ( BSD nc version ) and on many internet examples ncat can listen to udp and be used with the following options : -k which allows multiple connections -w 0 which terminates the current ...
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289 views

How to route all snmp request to remote deivces from a local machine through a proxy server

I have to forward all snmp request to remote deivces from a local machine to proxy server. Is it possible ? The actual requirement is like i have set of network devices that are only accessible ...
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209 views

systemd service - udp broadcast can't reach other machine

I have a service located under /usr/lib/systemd/system. This service runs the app that i've been developing (.net core 2.0). Same app runs on different machines (centos7 both). They use udp sockets to ...
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207 views

UDP socket in UNCONN state when using iproute2's ss

While editing some firewall rules on a machine that has an OpenVPN client running, I was trying to determine its remote port, as I usually do, using ss. # ss -anup | grep openvpn UNCONN6528 0 0....
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How to confirm if rsyslog transmit only UDP mode

We have rsyslog conifigured and configured is as below $ grep -vE '^#|^$' /etc/rsyslog.conf $ModLoad imuxsock # provides support for local system logging (e.g. via logger command) $ModLoad imklog #...
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705 views

Send UDP Packet to Memcached via Netcat

I am attempting to send the stats command to memcached via netcat, however, I am not getting anything back from memcached... I have tried echo "stats" > commands.txt nc -u 127.0.0.1 11211 < ...
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139 views

Application cannot receive UDP packet from Sony camera

I have a scenario with three devices: Android-Smartphone, Linux-Laptop (Linux mint) and a Sony a7R camera. My goal is to talk to the camera using the laptop and Sony's http-SDK via WiFi (Cam opens an ...
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Debian configure OpenSIPS for Websocket and UDP

I'm trying to configure OpenSIPS with OverSIP so that I could make a SIP call between a webrowser and a sip client app like Yate or Linphone. The call between two client apps (Yate/Linphone) works ...
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UDP Multicast not seen on PiZero w/ Raspbian

Looking for help troubleshooting my missing UDP Multicasts. Some background... So I finally got an Amazon Echo and was playing with fauxmo on my PiZero to see if Alexa could find my device, but she ...
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529 views

UDP hole punching with a third party

I am now convinced that direct "UDP hole punching" between 2 people each of them behind a NAT, without 3rd party server is really difficult / sometimes impossible (see question here and my answer ...
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507 views

What is the OpenVPN port range?

The default UDP port for OpenVPN is 1194. Is there a port range for OpenVPN, and if that is the case, what is the port range?
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267 views

Why is /proc/net/snmp not showing Udp InCSumErrors?

I'm running Oracle Linux 6.5, kernel 2.6.32-431.5.1.el6.x86_64. When I look at the Udp snmp stats it does not show me InCsumErrors. How can I see this stat? cat /proc/net/snmp | grep Udp\: Udp: ...
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1answer
776 views

UDP or TCP hole punching to connect two peers (each one behind a router)

I'm trying to connect directly (without 3rd party server) my computer to a friend's computer. We are both behind a ISP router, and would like (as a challenge!) to connect without modifying the router ...
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1answer
2k views

UDP port unreachable although process is listening

I am experimenting with communication over UDP port 6666 (the goal is setting up a listener for netconsole, but that's not really relevant here). On the listening side, nc -luv 6666. On the sending ...
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299 views

Why does a UDP client send 1Gbit speed to 100Mbit server?

I've just found out that in a simple UDP client/server application I wrote on Linux userspace, the UDP client (1 Gbit Ethernet interface) sends the data with 1 Gbit speed to a UDP server which has ...
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1answer
1k views

Cannot see packets arrive on application socket that were seen by Wireshark

Using Ubuntu 14 I have a Linux machine where there are two interfaces: eth1: 172.16.20.1 ppp0: 192.168.0.2 ppp0 is connected to a device which has a PPP interface (192.168.0.1) and a WAN interface (...
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1answer
759 views

High network latency after incoming UDP bursts [Solved]

This has been crossposted to https://forum.rocketboards.org/t/high-network-latency-after-incoming-udp-bursts/1266 I have an application sending UDP packets over a RAW socket (defining ETH, IP and UDP ...
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write error for rmem_max on Angstrom

I am trying to tune the UDP receive and transmit buffer size. According to my real time application needs, I need to configure the Tx buffer as 6 bytes and Rx buffer as 22 bytes. I am running Angstrom ...
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2answers
845 views

Redirecting specific UDP traffic?

I am trying to forward UDP traffic to/from a specific IP to a pseudo-interface: iptables -I FORWARD -s [WAN-IP] -p udp -j ifb0 I have also tried (without success): iptables -A OUTPUT -d [WAN-IP] -p ...
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5answers
3k views

Ubuntu - UDP Traffic on port 123

I have noticing that, lately, my Odroid's ethernet LED is constantly blinking, even when I'm expecting no traffic. I ran iptraf and, besides the attempts of SSH brute force guess attempts (that are ...
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474 views

Limiting socat udp to receive one packet or timeout

When testing certain multicast connectivities in the past I have been using socat to do this: socat -u UDP4-RECVFROM:12345,add-membership=224.1.2.3:eth0,fork,reuseaddr,readbytes=32 SYSTEM:"hexdump -C"...
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Prioritize UDP over FTP, SCP, etc. in Linux

I have a setup wherein one "master" Linux system communicates with 3 "slave" systems also running Linux on a dedicated Ethernet interface(just the master & the 3 slaves). The slaves send data to ...
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1answer
171 views

Transmission-Daemon not working (Debian 8 / OpenVZ) UDP Issue

I'm trying to install transmission on my VPS (under OpenVZ) to download torrents on it. When running something like: transmission-cli example.torrent It'll print: transmission-cli 2.84 (14307) [...
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1answer
374 views

Responses from multicast 255.255.255.255

On one particular box, i cannot get responses to broadcasted messages to (255.255.255.255). For example Sending DHCPDISCOVER DHCPREQUEST on wlan0 to 255.255.255.255 And see even responses from ...
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1answer
55 views

Do incoming LAN UDP packets create an entry containing senders MAC in receivers ARP table in Linux?

When Linux receives a UDP packet originating from a sender having a LAN source IP, will Linux put the source MAC address of this packet along the source IP address into the ARP cache table?
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409 views

Beaglebone Black not able to send raw UDP Packets with Python to laptop running Ubuntu 16.04

I created a Python 3.6 script that creates a raw UDP Packet over ethernet to a system with a known MAC Address and IPv4 Address. This script is running on a Beaglebone Black (BBB) that is connected ...
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2answers
2k views

Why does the udp port not open?

I am investigating how to open a UDP port, specifically the port 1194. This is what I've done: Check if the port is opened: % sudo nmap –sU –p 1194 <hostnameOfMyMachine> -> PORT STATE ...
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582 views

How to display an UDP connection?

ss and netstat seem to not be working. Adobe Flash RTMFP protocol creates a lots of UDP connections. I want to know, who is connected to me. I can see intense data-send traffic from the monitor. I ...
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1answer
4k views

Sending UDP packets to a destination

On my Linux machine, I am receiving UDP packets from another machine. When I receive the UDP packets, I get the message "Listening on UDP port : 8999" This is triggered by the following command ...
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1answer
906 views

Why is my trace route (mtr) binding a UDP port when it runs?

I occasionally audit the open ports on my machine to make sure I fully understand my attack surface. When I did this today, I discovered that mtr was listening on a high UDP port (which seemed to ...
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1answer
2k views

Can't receive UDP packets wireshark sees them

I have an application_A in HOST_A sending UDP messages. In HOST_B I am able to see the UDP packet in wireshark but application_B (running in HOST_B) doesn't receive them. I can verify that ...
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1answer
400 views

How does the TCP/IP stack handle UDP packets to local host and a destination address of yourself?

I am trying to understand how the network stack (TCP/IP) handles a UDP message to localhost. I am assuming it goes down the stack and gets to the IP layer, if it sees localhost it then sends it back ...
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465 views

When does the kernel cut UDP datagram into MTU chunks?

I need your help/hints/remarks on an issue I'm having. Thanks Here is some context : I have two application(A1 & A2) handling PDUs with a max size of 1700bytes. Each app is on a different card(C1 ...