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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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Need a live UDP echo Server IP and port

I require to test my UDP program using echo server. I have tested this application in LAN but now I require it to test it in Internet. Is there and globally recognize freely available well known ECHO server that I can use directly in my application…
Amit
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How common are dropped packets in communications within a data center?

Let's say I have 2 machines in the same data center but not necessarily in the same rack. How common would dropped packets be when sent using UDP between these two machines? I'm asking under the assumption that since there are only a few switches…
z8000
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UDP packets seen on interface level but not delivered to application on RedHat

I have a problem with receiving UDP traffic on a RHEL6 server. When capturing the traffic with tcpdump, the packets are visible (checksums are correct, the destination IP and MAC match the machine's ones). However the application listening on the…
wojciech_k
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Symmetric NAT and UDP Hole Punching

I've read this question, but the explanation of Symmetric NAT wasn't detailed enough. Please could someone help me to understand the following paragraphs? I read this about Symmetric NAT: Each request from the same internal IP address and port to a…
john
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Higher rmem_max value leading to more packet loss

The rmem_max Linux setting defines the size of the buffer that receives UDP packets. When traffic becomes too busy, packet loss starts occurring. I made a graph showing how packet loss increases depending on the incoming bandwidth. (I use IPerf to…
Nicolas Raoul
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How to start iperf3 server in UDP mode?

I would like to test UDP connectivity with iperf3 but do not know how to start it in UDP server mode. iperf3 -s only opens a TCP socket: root@srv ~# lsof -i -P | grep iperf3 iperf3 21030 root 3u IPv4 15606995 0t0 TCP *:5201…
WoJ
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Is it possible to duplicate a UDP unicast stream with iptables?

I have a proprietary system which transmit a udp video stream from unit #1 (192.168.1.1) to unit #2 (.1.2). I can't make changes to this system, and I'm trying to clone this udp stream so I can access it in a different program. This program will do…
Håkon K. Olafsen
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HTTP, TCP, UDP and connectionless

I am a bit confused with HTTP lately. Some facts are that TCP can operate connection orientated or connectionless, this I understand. TCP though is connection-oriented while UDP is connectionless which is used when the message itself can fit…
What'sTheStoryWishBone
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How are UDP source ports selected?

I just did a packet capture from my machine and filtered out all the UDP connections. I saw certain connections using what appears to be a randomly generated UDP Source port, and certain connection using the same Source port as the UDP Destination…
Eddie
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UDP traversal through router automatically without router port forwarding?

Everyone knows the router is working like a firewall. Without port forwarding, a connection (no matter TCP or UDP) cannot be initiated from outside of the router. However, if a user initiate a TCP connection successfully from internal of the router,…
Jack
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Are DNS queries encrypted?

I wonder if DNS queries are encrypted. If so, can you briefly explain the process as I suppose for an encryption to take place, there should at least be a minimum common ground between two parties (like a share of a key), but since DNS uses UDP and…
Ninja Bug
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Why multicast UDP can be slower than unicast UDP?

I have two machines (with Centos 7.3 on both) connected via 1G switch. When I measure UDP thoughput between macines with iperf it gives about 850 Mbit/s. However when I measure multicast UDP thoughput it results in something like 95 Mbit/s (almost…
Alexei Osipov
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rsyslog udp forwarding truncates at 2048 characters

Rsyslog on a RHEL 6 server is receiving messages locally on port 514 UDP. These messages are sometimes much larger than normal syslog message sizes. I am seeing rsyslog handle all of the messages just fine, it writes to the local files without…
nictrix
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Tool for forwarding UDP packets Windows

Windows Server 2008 I use portproxy interface to forward traffic , but I looked into the msdn page and I noticed it doesn't support udp protocol . protocol Specifies the protocol to use. Currently, only Transmission Control Protocol (TCP) is…
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Netcat UDP File Transfer?

Is there any way to send a file (picture or video) using Netcat and UDP. It defaults as TCP, but I would like to send using UDP. I tried simply adding -u to the nc command, but that didn't work. Here are the two commands I'm using: cat File.jpg | nc…
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