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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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How does an Access Point handle broadcast packets from the wired side?

I have an Cisco AP 1242AG autonomous AP connected to L2 switches. Let's say I have 100 wired devices each sending 2 broadcast UDP packets per second. Obviously these packets will reach the Access Point switch port, but will the AP actually send…
atomicluis
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UDP Overflow / UDP Drops on Standby Postgres Service

I am stumped trying to prevent an overflowing UDP buffer on a standby Postgres service. Any help would be most appreciated. Essentially a UDP buffer associated with the pg_standby process on my localhost interface gradually fills up once I start…
Daniel C
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How to force use of tcp instead of udp for rpcbind?

I'm trying to use tcp/111 for rpcbind under Debian Wheezy instead of udp/111. The portmap in Squeeze uses tcp/111 without any special configuration, but Wheezy fails. Even numerous sites (as well as RFC) says TCP or UDP is selected dynamically, or…
Matej Kovac
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Per-packet round-robin load balancing for UDP

I need to load-balance UDP traffic between a number of "realservers" and do it in a truly round-robin fashion. I've started with keepalived, but unexpectedly discovered, that LVS treats UDP traffic as a "connection" (whatever that is in terms of…
shylent
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Traceroute, ICMP, UDP and TCP

When does traceroute use TCP? Or does it just use UDP, also why does Traceroute use UDP on MacX and ICMP on windows? I thought ICMP just contains a message saying what caused the error of a packet and does not transmit segments like TCP and UDP.
user171131
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possible UDP attack on BIND?

hello everyone, i was surprised last month when my EC2 instance (ubuntu precise server), that is supposed to be under the free tier still, accumulated lots of traffic... today, while checking my current billing statement, i noticed i already have…
Waleed Hamra
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Why is UDP slower than TCP on Ubuntu Server?

I transfer data between two Ubuntu Servers (12.04) via iperf on 1Gb LAN. iperf -s <-> iperf -c -n2G TCP speed = 925 Mbits/sec iperf -su <-> iperf -uc -b1G -n2G UDP speed = 810 Mbits/sec Jitter = 0.016 ms Lost = 0 ..…
Rom098
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Script to find the address udp packets are being sent to?

Here is the scenario. I have an IP address 1.2.3.4 port 2000 sending udp packets to one unknown IP. I would like to find the unknown IP so I can block it with iptables. Is there a way to do it with a script? Right now I am doing it manually by…
Bob
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Rate of UDP packet loss over WLAN

While testing something with TFTP I noticed lots of timeouts (and slow speed as result) when I used my WLAN - and no problems when using a network cable. A quick test program sending/receiving UDP revealed that there are about 3-5% packets…
Martin
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How can I reject all incoming UDP packets except for DNS lookups?

I set my server to reject ALL incoming UDP packets, to prevent UDP floods. However, I was told that because I use my own domain and server for my nameservers, this can cause some problems. How can I get around that? My firewall is iptables, my…
Rob
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Find the process listening on a port (not showing in lsof)

Update: The port was opened by NFS. I figured this out by configuring NFS to listen on a known port. Using Ubuntu 18.04 I want to know which process or kernel function listens on UDP port 38637. I have researched this problem and found similar…
jchook
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Routing TCP packets to a local UDP port

A third party server sends UDP packets to an EC2 instance we've set up and I'm trying to route those packets to my local machine. The client sends these packets to port 8975 To that effect I first established an ssh tunnel to my ec2 instance ssh -4…
Jayaram
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UDP. Sending speed is limited by the minimal Ethernet adapter configuration

I have 1Gbit Ethernet adapter on my computer. And I have the other computer with Ethernet adapter 100Mbit. The both in one LAN and connected through the 1Gbit switch. 1 Test: I try to send from my computer(1Gbit) to the other(100Mbit) the packets by…
Vitali Kuzniatsou
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UDP broadcast to remote site

I've been trying to find a way to allow a sever in a certain subnet to send UDP broadcasts over multiple subnets. The scenario is this: In network A (192.168.1.0/24) we have a backup server (using urbackup), the server uses automatic discovery of…
Alex Zel
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BIND ICMP Port Unreachable responses

I'm experiencing random issues on a DNS resolver running BIND 9.8.2 (RHEL6) behind a loadbalancer. The loadbalancer is actively probing the server with a DNS query to find if it's alive, and every now and then it gets a "Connection refused" (ICMP)…
André Fernandes
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