Server Fault Stack Exchange
Server Fault Stack Exchange

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

542 questions
21
votes
6 answers

How is the MTU is 65535 in UDP but ethernet does not allow frame size more than 1500 bytes

I am using a fast ethernet of 100 Mbps, whose frame size is less than 1500 bytes (1472 bytes for payload as per my textbook). In that, I was able to send and receive a UDP packet of message size 65507 bytes, which means the packet size was 65507 +…
nikku
20
votes
6 answers

Why would a university block incoming UDP traffic with destination port 53?

From my understanding DNS uses UDP and port 53. What undesirable things could happen if incoming UDP packets to port number 53 weren't blocked? UPDATE: Packets originate or are destined to the university-operated local DNS server or…
Daniel Kobe
  • 313
  • 2
  • 3
  • 8
19
votes
2 answers

Reduce firewall rules by half - one iptables rule for tcp and udp

I have a number of iptables rules on my firewall that look like this: iptables -A zone_lan_forward -p tcp -d 1.2.3.0/24 -j ACCEPT iptables -A zone_lan_forward -p udp -d 1.2.3.0/24 -j ACCEPT Is there a shortcut for having two rules - one for tcp and…
Big McLargeHuge
  • 393
  • 3
  • 4
  • 14
18
votes
1 answer

Vendor whitepaper says: 5Mpps no prob. I'm already hitting a wall at 120kpps. Where's the bottleneck?

HP's whitepaper on their QLogic (fka Broadcom) NetXtreme II adapters, which includes the specific NIC that I'm testing, states (page 7) that their small packet performance for packets up to 256 bytes/packet is above 5,000,000 packets/sec. In my…
Evgeniy Berezovsky
  • 861
  • 1
  • 8
  • 27
17
votes
6 answers

Solution to route/proxy SNMP Traps (or Netflow, generic UDP, etc) for network monitoring?

I'm implementing a network monitoring solution for a very large network (approximately 5000 network devices). We'd like to have all devices on our network send SNMP traps to a single box (technically this will probably be an HA pair of boxes) and…
Christopher Cashell
  • 9,128
  • 2
  • 32
  • 44
15
votes
2 answers

Verify connectivity to a server on a UDP port

I want to know if a HP-UX machine can communicate to a remote machine (which I don't have control over) on a particular port using UDP. I tried telnet, but it doesn't look like it supports UDP. I would use netcat, but I was unable to find any…
skinp
  • 749
  • 1
  • 7
  • 19
14
votes
4 answers

tcpdump increases udp performance

I'm running a set of load tests to determine the performance of the following setup: Node.js test suite (client) --> StatsD (server) --> Graphite (server) In short, the node.js test suite sends a set amount of metrics every x seconds to a StatsD…
Ruben Homs
  • 149
  • 7
14
votes
3 answers

How to connect to a udp port command line?

This is what I tried,but seems not working : [root@ ~]# netstat -a|grep 48772 udp 0 0 *:48772 *:* [root@ ~]# telnet localhost 48772 Trying 127.0.0.1... telnet: connect to address…
yum
  • 569
  • 5
  • 9
  • 17
12
votes
2 answers

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are connected via a single 1Gb switch. Testing UDP…
Evgeniy Berezovsky
  • 861
  • 1
  • 8
  • 27
12
votes
3 answers

Where is the documentation that states TCP and UDP source port should be over 1024 and random?

I am having a hard time to find where it is documented that the source port should be random and in the range 1024-65535. In which RFC is this documented? Edit: First reference for privileged ports is in RFC2623 It seems that this is depending more…
Mircea Vutcovici
  • 17,619
  • 4
  • 56
  • 83
11
votes
2 answers

mosh-like port forwarding

This is on linux, connecting to linux servers: I love mosh, but it doesn't support port forwarding, and likely won't for a while since it's been almost a year now and it hasn't happened yet. port forwarding over ssh is great, but because my laptop…
Marc Merlin
  • 241
  • 2
  • 6
11
votes
5 answers

How to list all requests to udp sockets?

I'm operating a couple of server daemons that use udp to communicate with large number of clients. How do I find and list out all the active udp "connections" that are talking to the servers in order to estimate the num of active clients that are…
Flint
  • 631
  • 5
  • 10
  • 18
10
votes
3 answers

Windows Server 2012 - RDP over UDP not working

I have a Windows Server 2012 (not R2) machine, hosted within Hyper-V virtualization with RD Session Host & RD Gateway installed. It is used to run a desktop GIS application. The performance over WAN is quite poor. I added UDP port to NAT in order…
Mirko
  • 101
  • 1
  • 5
10
votes
3 answers

Load Balancing DNS Servers: UDP / TCP

I have been asked to rebuild our load balancing infrastructure in the data center. The original request was to load balance FTP servers. I tried doing that using the current load balancer (Piranha / LVS), but didn't get it up and running. Not just…
Mosh Pit
  • 339
  • 2
  • 4
  • 13
10
votes
1 answer

OpenVPN Error : TLS Error: local/remote TLS keys are out of sync: [AF_INET]

Fist off thanks for reading this, I appreciate any and all suggestions. I am having some serious problems reconnecting to my OpenVPN client using Riseup.net's VPN. I have spent a few days banging my head against the wall in attempts to set this up…
Lucidity
  • 103
  • 1
  • 1
  • 5
1
2
3
…
36 37