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Questions tagged [udp]

UDP stands for User Datagram Protocol. With UDP applications can send messages (datagrams) to other hosts on a network without requiring prior communications to set up special transmission channels or data paths.

Because UDP doesn't rely on handshaking to guarantee that packets arrive and in order it can be seen as an unreliable protocol, but for real time systems where acting on the data immediately is the most important consideration not having to wait for delayed packets is a distinct advantage.

UDP is just one communications protocol on the web. Others include:

  • Transmission Control Protocol (TCP)
  • Internet Control Message Protocol (ICMP)
  • Hypertext Transfer Protocol (HTTP)
  • Post Office Protocol (POP3)
  • File Transfer Protocol (FTP)
  • Internet Message Access Protocol (IMAP)

UDP on Wikipedia

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Difference between /dev/udp and netcat

I have a syslog server listening on localhost:514 as UDP and would like to write messages to it on that port. (Using Ubuntu 14.04) If I run either of these commands from bash it prints the date every 2 seconds to syslog # Using netcat while true;…
user779159
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Why does VPN IPSec client use UDP?

The VPN I use on my home Windows computer to connect to my company's servers is a Cisco client. The client is configured to use "IPSec over UDP (NAT/PAT)". Why would you use UDP, an "unreliable" protocol, for a secure tunnel? Wouldn't the…
user35042
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Can I test broadcast packets on a single machine?

I want to have a server sending broadcast UDP packets and two other clients, in the same machine, receiving them. Can I do that somehow? What IP address would I use? @gravyface gave me hope but I tried: Server sending to 127.255.255.255:54321 and…
chrisapotek
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Hardware/topology recommendations for low latency UDP network

I'm setting up a LAN comprised of 60 end nodes that are receiving a high volume of UPD datagrams from one master server. The server sends 60 unique datagrams every 100ms, each datagram is 64 bytes. This means I'm sending 38400 bytes per second. Each…
Mattias
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Troubleshooting UDP multicast on Windows

I'm a programmer, not a system adminstrator, so please forgive my administrative naivete. My software, written in C#, relies on UDP multicasting. One machine, the server, streams events to an known UDP group address (configurable, but 224.130.103.5…
Aaron Haspel
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How does UDP track connections?

If UDP does not establish a connection as TCP does.. it seems the only way it could track connections is source ip/port and destination ip/port. Is this correct? So, I guess there are special packets for Connection Refused and Connection Reset. Is…
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How to measure and minimize UDP packet loss

I sometimes face voice break when calling through a VOIP application. Since all VOIP applications uses UDP for data transmission, is there any tool in Linux to measure the amount of packet loss and measure the performance of the network. What could…
Supratik
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Should I use TCP or UDP to run a web server

I have just installed Apache web server on my computer. I have managed to use it locally (I can open index.php from my computer using my web browser). But I would like to make my web site available publicly. I found out that for that I need to open…
Roman
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What is the equivalent of Cisco's 'ip virtual-reassembly' for a Juniper ISG 2000

I tested my dns servers with the oarc test and my size limit is at least 1403 bytes. I performed the same test before my Juniper ISG 2000 and the result is 2047 bytes. According to the chapter IP "Fragments Filtered" and this article, I think I…
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php-fpm php_network_getaddresses calls randomly start failing with bad udp cksum

We're running a number of web servers (nginx, php5.6-fpm) on ubuntu instances on AWS. They've been running fine for a number of months, but in the past few days we've started getting issues where after an instance spins up everything is fine, but…
Liam Wiltshire
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How to block 111 udp port via iptables?

I've got an issue related to block 111 port only for udp. For tcp it was blocked without any problem. This port is used by application rpcbind. I test it via netcat. This is my iptables. It contains empty chain FORWARD, because I've removed all…
ANtlord
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rsyslogd not listening udp 514

I have Debian 3.2.65-1+deb7u2 with rsyslog 5.8.11 udp 514 $UDPServerRun 514 and $InputTCPServerRun 514 are uncommented. Why it is not listening to that udp port?
user354663
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Segmentation fault when running nuttcp inside Docker

I am measuring the UDP throughput between two Docker containers that are connected by Docker's native overlay network. I already used iperf but also want to measure the throughput with nuttcp. But when I am starting the server instance and then…
arne.z
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Why some iptables DNAT rules don't work until reboot?

My iptables DNAT rules don't work until reboot. If I reboot my server, all of the rules work. Desciption of the architecture : Tens of hosts (senders) send some UDP packets (one-way on a specific port 9999) to my Linux router. This Linux router use…
kranteg
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Is OpenVPN UDP vulnerable to heartbleed?

Is OpenVPN UDP vulnerable to heartbleed? I need to decide if I'm going to rebuild some servers, but they are very carefully firewalled; 1194/TCP is one of the firewalled ports (yay whitelist!). 1194/UDP is used (mission critical).
AMADANON Inc.
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