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.

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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. ...
TheSquad's user avatar
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6 votes
3 answers
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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 ...
Dani Cela's user avatar
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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<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 As you can see, no broadcast address! :( ...
chrisapotek's user avatar
6 votes
1 answer
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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 ...
c_oreills's user avatar
6 votes
1 answer
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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 ...
Yury's user avatar
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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....
mycroes's user avatar
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6 votes
2 answers
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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 ...
Guillermo Prandi's user avatar
6 votes
1 answer
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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 1000000000 ------...
TJF's user avatar
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2 answers
32k views

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 ...
Roman's user avatar
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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" ...
user35042's user avatar
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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 ...
chrisapotek's user avatar
5 votes
4 answers
10k views

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 ...
700 Software's user avatar
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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 ...
Aaron Haspel's user avatar
5 votes
3 answers
7k views

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 ...
Steffen's user avatar
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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 ...
Supratik's user avatar
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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 ...
user779159's user avatar
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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. ...
Mattias's user avatar
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2 answers
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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 "...
2xyo's user avatar
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0 answers
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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 ...
Alnitak's user avatar
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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 <addr> -n2G TCP speed = 925 Mbits/sec iperf -su <-> iperf -uc<addr>...
Rom098's user avatar
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2 answers
13k views

tcpdump truncates to 1472 bytes useful data in UDP packets during the capture

I am writing an application which work with network. To perform some tests I need to reproduce the flow which I had a day before. But at the same time it is not allowed to stop the current working ...
Gavelock's user avatar
4 votes
4 answers
16k views

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 ...
Rob's user avatar
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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!). ...
AMADANON Inc.'s user avatar
4 votes
1 answer
35k views

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 ...
ANtlord's user avatar
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4 votes
2 answers
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Multicast IP Addresses

I posted this on StackOverflow and was told it might be more appropriate here. I'm having trouble understanding how multicast addresses work. First off, is it true that if I have N clients or peers ...
Josh G's user avatar
  • 143
4 votes
2 answers
1k views

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 ...
Liam Wiltshire's user avatar
4 votes
1 answer
733 views

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 ...
Waleed Hamra's user avatar
4 votes
2 answers
8k views

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 ...
shylent's user avatar
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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 ...
kranteg's user avatar
  • 222
4 votes
3 answers
17k views

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 ...
user171131's user avatar
4 votes
1 answer
209 views

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 ...
Bob's user avatar
  • 195
4 votes
1 answer
783 views

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 ...
arne.z's user avatar
  • 357
4 votes
1 answer
9k views

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's user avatar
4 votes
1 answer
6k views

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 ...
atomicluis's user avatar
4 votes
1 answer
6k views

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 ...
Matej Kovac's user avatar
4 votes
2 answers
5k views

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 ...
user avatar
4 votes
0 answers
1k views

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 ...
jchook's user avatar
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4 votes
0 answers
1k views

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 ...
Daniel C's user avatar
3 votes
1 answer
14k views

How do I add a broadcast IP to the loopback interface under os/x using ifconfig when my machine has no network? [duplicate]

I'm new to advanced network administration and I would like to do some testing with UDP broadcasting, so I need a broadcast address on my loopback interface. The machine is offline, in other words, ...
bandodeotarios's user avatar
3 votes
1 answer
4k views

Cat a file(raw) to UDP at specific bitrate

I'm looking for a way to transfer a file over UDP at an specific bitrate. I can use netcat for example like this: cat file | nc -u 192.168.x.x 5000 And I use a custom application to listen at port ...
user185165's user avatar
3 votes
1 answer
8k views

Block an IP for UDP

I am under UDP flood attack. I used following protections to solve it: iptable IP ban: iptables -I INPUT -s 37.187.231.xxx -j DROP Tried another iptable syntax /sbin/iptables -I INPUT -i eth0 -s ...
Niky's user avatar
  • 33
3 votes
2 answers
417 views

Finding the executable sending packets to a specific IP Address?

We host Game Servers off of Windows Server 2008 machines, and we just received a report that one of our customers is using their server to do some type of UDP attack. The person being attacked ...
Aidan Knight's user avatar
3 votes
2 answers
2k views

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 ...
Jayaram's user avatar
  • 153
3 votes
1 answer
3k views

tcpdump udp data capture latency

I am using tcpdump to capture UDP packets and analyze network latency between a UDP broadcaster and my server. To calculate latency I compare the source host timestamps reported in UDP application ...
Robert Kubrick's user avatar
3 votes
2 answers
274 views

Port Knocking and TCP/IP within the OSI model

I have read that Port Knocking can be subject to false negative (type II error) due to the optimization techniques of TCP/IP. A correct port knock given by the client may be read as incorrect by the ...
jtrip's user avatar
  • 41
3 votes
1 answer
3k views

What is the difference between bind, network (interface) and multicast addresses?

The DatagramSocketImpl in Java has a joinGroup method that takes a socket address (IP and PORT) plus the interface address (IP and PORT). I am trying to understand the difference and purpose of each ...
chrisapotek's user avatar
3 votes
1 answer
11k views

Forward broadcast to fixed IP using IPTables

I need to forward (route) broadcast packets from several wireless clients to a single server in the fixed network. The wireless and fixed network are not bridged for security reasons. With the ...
MightyZen's user avatar
3 votes
2 answers
873 views

netstat reports UDP ports with no owning process

When I run netstat -avp udp I get a slowly growing number of ports. It grows about 100 an hour but the rate varies considerably. When I close the process, the ports do not disappear from the list. ...
Simon G.'s user avatar
  • 131
3 votes
1 answer
2k views

nginx config for reverse proxying UDP traffic (minecraft app) - 90 message too long

Trying to proxy udp traffic. nginx doesn't throw any error about the configuration. The client connects until half-way (it says it could reach the end server) but the connection then gets stuck and ...
seb's user avatar
  • 93
3 votes
1 answer
686 views

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 ...
Vitali Kuzniatsou's user avatar

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