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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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Block all incoming DNS requests EXCEPT from IPs x,y,

I want to block all incoming requests on my two DNS servers APART FROM certain IP addresses e.g. IP of 1.2.3.4 will be allowed to make requests but NOBODY else will. How do you do this with iptables? Many thanks.
ale
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How to create UDP proxy using iptables

I have a server running UDP server on port 50000. This server receives updates from clients, and pings back the clients every 5 seconds to the socket they were connected from. Now I want to redirect all the traffic to and from this UDP server via…
arikfr
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UDP Sessions and Ephemeral Port Selection

I would like to ask community to help me finding answers to the following questions: According to RFC 6056 an operating system should pseudo-randomly select ephemeral ports for each transport layer connection. For TCP, which is stateful protocol,…
Yury
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How to determine which process is sending UDP packets once per hour?

I was doing a packet capture as part of a development project and saw some odd traffic coming from my machine in the capture file. About every 3600 seconds, a NAT-PMP request is being sent to the IP "1.1.168.192". (Kind of amusing, looks like…
fdmillion
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UDP hole punching still required in IPv6, even without NAT?

Background (skip ahead for question) IPv4 needed NAT for address conservation. The firewalling properties of NAT were also beneficial for security. IPv4 NAT firewall rules are "block incoming packet remote-address:port -> local-address:port, unless…
Peter Stock
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UDP port appears to be in use but is not shown in netstat or TCPView

I've encountered some strange behavior I don't understand. I'm installing software on a Windows 2003 Server. This software needs to bind to a specific UDP port an all TCP addresses in order to listen to requests. I seem to be able to bind to several…
Guillermo Prandi
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Problems with MDNS flooding on port 5353 UDP

I am running into a big issue at a small network i manage. This network is an Apple network, with airport extremes, expresses, mac book pro's, imac's, ipads, iphones etc... I went to add something to this network today and noticed lights flashing…
Dani Cela
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Does hole punching require a UDP rendezvous server Or could it be a TCP one?

I'm trying to get my head wrap around this issue... I would like to connect two users... Those users are already connected to a TCP server, which is aware of both public ip and connection TCP port. I was hoping to use the existing connection to the…
TheSquad
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How to add a broadcast address to loopback with ifconfig on a OS/X?

I am trying to use ifconfig to turn on broadcast on my loopback interface. It currently reads: lo0: flags=8049 mtu 16384 As you can see, no broadcast address! :( :( :( I tried this on OS/X but it did not work and it…
chrisapotek
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OpenVPN failing on self-signed certificate over udp, works over tcp

I have the following server.conf: # OpenVPN 2.x config proto tcp port 1194 dev tun-vpn dev-type tun server 10.8.0.0 255.255.0.0 push "route 172.16.0.0 255.255.0.0" push "dhcp-option DOMAIN mydom.com" push "dhcp-option DNS 172.16.1.1" #…
mycroes
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Why is it 3-way-handshake and not more?

TCP uses the 3-way-handshake mechanism. I understand how it works pretty well but I wonder why it's not 4, or even 5-way? Is it because that's too much overhead and is not needed?
IcySnow
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iperf max udp multicast performance peaking at 10Mbit/s?

I'm trying to test UDP multicast throughput via iperf but it seems like it's not sending more than 10Mbit/s from my dev machine: C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b…
TJF
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Netcat - Listen for Multiple UDP Connections

I'm trying to use netcat to debug SIP calls, which communicate over UDP. Is there a way to get the same netcat instance to listen to multiple UDP Connections? I've tried connecting to the same netcat session from two different hosts and the second…
c_oreills
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Disable NIC Receive Side Scaling hashing

On a benchmark lab system running Fedora Core 27 I've got Intel X710 10GE cards and 12-core Xeon processors, configured with 12 NIC queues and RX Flow Hashing based on both IP addresses and port numbers. This results in uneven balancing between…
Alnitak
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How to allow UDP broadcast between interfaces on a Cisco ASA 5506-X

I have a CISCO ASA 5506-X with 4 configured interfaces and a set of access-lists etc. It is configured via CLI and is running in routed mode, not transparent. Everything is running well, but now I have a problem I could not yet solve: One of the…
Steffen
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