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.

learn more… | top users | synonyms

0
votes
0answers
6 views

Monitoring an Ethernet network

Scenario, a server farm with 100 servers running Linux, mainly IPv6 UDP traffic. From a system administration perspective, what is the best way to isolate a faulty server within an Ethernet network? ...
2
votes
1answer
24 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?
0
votes
2answers
2k views

lots of UDP_IN Blocked errors

Since I have reinstalled my OS, I'm getting lots of UDP_IN Blocked errors in my messages log. Can anyone kindly explain what the error say exactly and what I can do to get rid of this error. Aug 8 ...
3
votes
2answers
4k views

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 ...
3
votes
2answers
6k 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 ...
-1
votes
0answers
31 views

UDP tunnelling outside OpenVPN

this is my first post. I have already looked for solutions but I haven't solved my problem at all actually. I have a linux server connected to a OpenVPN server whose service I pay for. This provider ...
17
votes
2answers
37k views

listen to UDP data on local port with netcat

netcat -ul -p2115 fails with a usage statement. What am I doing wrong? Thanks!
0
votes
1answer
29 views

Iperf3 keeps hanging when running UDP test

I wrote a Python program that runs iperf3 in a for loop with different datagram sizes. I am using Python's subprocess.call function to run iperf3 like this: iperf3 -u -c 185.82.21.60 -b 100M -t 5 -l ...
0
votes
1answer
1k views

OpenVPN client opens a random UDP port?

We are noticing this on a number of our openvpn clients: [root@box ~]# netstat -tulpn | grep openvpn udp 0 0 0.0.0.0:53950 0.0.0.0:* ...
5
votes
2answers
10k views

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 ...
1
vote
0answers
12 views

Is there a way to tell a machine accesible via a gre tunnel to join multicast groups via pimd or smcroute?

this has been stumping me for some time and would love any help on this. So I am subscribed to a data vendor through an intermediary firm. The intermediary firm has physical connections to the data ...
3
votes
1answer
26 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 ...
1
vote
0answers
61 views

Joining a UDP multicast through a server on the other side of the tunnel

I've drawn a diagram below to help with this question! So a company published a multicast UDP feed (company A) and another company connects to it (Company B). I have a point-to-point tunnel to ...
1
vote
1answer
40 views

UDP Server behind Gcloud load balancer: receive ok, reply fails

I have a UDP server set up (on a VM) behind the Google Cloud network load balancer. The server is bound to 0.0.0.0. The UDP server can receive messages that were sent to the balancer, but replies do ...
5
votes
5answers
8k views

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 ...
1
vote
0answers
19 views

rx_queue value in /proc/net/udp grows to twice the SO_RCVBUF value

When using an SO_RCVBUF of 10485760 (which is also the current limit as stipulated by sysctl's net.core.rmem_max setting, and sending UDP packets faster than the receiving side is able to handle, the ...
2
votes
0answers
174 views

How to resolve UDP packets being dropped given netstat reporting SndbufErrors

I have a server instance on an OpenStack that at a pretty high load starts loosing UDP packets. I captured all outgoing packets using tcpdump and some of them are missing, even though application logs ...
1
vote
2answers
27 views

how to run memcached on UDP ports only

How can i configure memcached to run on udp ports only on centos box ? Right now it is listening on TCP ports by default. Here is my memcached configuration file. cat /etc/sysconfig/memcached ...
2
votes
2answers
126 views

Minimal size of TCP communication

I am sending small amounts of data (up to 100 bytes) every 10 minutes from devices to TCP server. In my case overhead seems to be huge (we pay for each byte). I found that I have at least 7-10 packets ...
0
votes
1answer
56 views

How to make svlogd send logs via UDP

I am currently using runit + svlogd for supervising some applications, but when deploying to multiple machines, I have the need to centralize/unify the logs in a single place in order to simplify ...
0
votes
1answer
54 views

bandwidth monitoring by TCP/UDP port on Cisco 2960 or Linux

We have an international line between two sites with limited bandwidth. I want to monitor bandwidth usage between the two sites, and understand which type of traffic consumes the most. Ideally I ...
-1
votes
1answer
43 views

What is a TCP Relay and when is it used? [closed]

Tcprelay is a TCP connection forwarder with load balancing capabilities. If compiled with TLS support, it may be used as SSL encryption wrapper. What are some practical applications of TCP relay?
1
vote
2answers
319 views

(Simple) UDP Protocol - Networking

I know that UDP is an unreliable protocol where things can arrive out of order, fail to arrive completely, etc. I'm also aware that when using UDP for something like traceroute, packets that arrive ...
19
votes
6answers
5k views

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 ...
4
votes
3answers
6k views

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 ...
2
votes
0answers
101 views

How to use an IPv6 Edge router in an IPv4 network?

Background I have the following set-up: I use 6LOWPAN (IPv6 implementation in IEEE 802.15.4) on my sensor link that have IPv6 addresses (stateless) as aaaa::xx/64 It uses RaspberryPi (RPI) as an ...
1
vote
1answer
35 views

udp broadcast on port 25860

I used wireshark on my local network (to test it), and i noticed that there is a lot of udp packets send one broadcast, and the majority is coming from only one host. Theses udp packets are send on ...
0
votes
0answers
13 views

UDP destination address during port forwarding?

I have setup a connection using Qt in the LAN, PC1(192.168.1.195) will send UDP packets to PC2(192.168.1.201) with no problem. But now, PC1 and PC2 are now working under different routers. So now PC1 ...
2
votes
3answers
2k views

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 ...
3
votes
1answer
734 views

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 this from bash it prints the date ...
3
votes
1answer
2k 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 ...
4
votes
1answer
251 views

udp packet delays in my dedicated WIFI network - can i force UDP nodelay over wifi?

I have a dedicated app and network development for passing UDP packets over a wireless network. The totality of the network is a PC (Mac OSX or Linux) which sends the packet-->router/AP-->WIFI ...
2
votes
1answer
1k views

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. ...
-1
votes
1answer
275 views

What are the ports needed for L2TP VPN on Mac OS X Server 5.0.15?

I'm configuring a Mac as a server with a VPN service. So, I opened the ports listed as used by VPN in Apple documentation: UDP 500 -> 500 (+ESP and AH) UDP 4500 -> 4500 Any UDP -> 1701 (I got to ...
0
votes
0answers
11 views

CentOS Drupal Site/Domain Sending UDP Attacks on Different IPs [duplicate]

My Drupal 7 site is hosted on a Cent-OS 6.5 VM. The hosting service provider notified me about an malicious activity on site and site is sending UDP packets on different IPs. Following is data ...
5
votes
2answers
339 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 ...
13
votes
6answers
6k views

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 ...
1
vote
1answer
106 views

Can't connect to python server on LAN

So I have this python server which just returns the uppercase sentence which came as a input: from socket import * serverPort = 12000 serverSocket = socket(AF_INET, SOCK_DGRAM) ...
5
votes
5answers
7k views

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 ...
0
votes
0answers
21 views

Packets not being delivered to application

First of all sorry if this is not the right place. So... I have a problem. I'm working on a linux board (the distro is created with yocto, kernel is 3.10.17). I have several network interfaces (WWAN1 ...
0
votes
0answers
36 views

netcat UDP port test response issue

I am running a game server on a Windows Server 2008 VPS/VDS through port 12203. I want to be able to automatically restart the game server exe file if it crashes. So, my strategy is to use netcat to ...
0
votes
1answer
51 views

Why are duplicated UDP packets being dropped 10 out of 11 times by this iptables configuration?

I am trying to duplicate UDP packets flowing to port 50007 on an Internet address from devices on a local NAT network (192.168.12.0/24) with the intent of processing them locally (on ...
0
votes
2answers
94 views

How to connect a client behind a NAT router to an Asterisk server behind a NAT router?

I have an asterisk setup on a server. The local IP address is 172.22.9.200 and extenal IP address is 75.45.185.100. My client device is an android phone that is connected to a router and it which ...
-5
votes
2answers
74 views

Does UDP includes of source address?

Both UDP and TCP does not include source address, but how does it say UDP IP spoofing is easier than TCP? For example, the following webpage also says about UDP vulnerability. "Unlike TCP, UDP does ...
-3
votes
1answer
36 views

What does the following UDP connection mean? [closed]

What does the following entry mean? Is that mean someone has connected to the server from this IP or somthing else? Nov 23 15:33:54 www-prod-2 snmpd[1573]: Connection from UDP: ...
2
votes
2answers
992 views

Does Azure support UDP Broadcast?

I am aware that Azure supports UDP, but does it support UDP broadcast? I am wanting to use the Jenkins Swarm plugin, which requires UDP broadcast for new slaves to join the master.
1
vote
2answers
359 views

Strange UDP/TFTP Problem

My TFTP client only seems to be getting responses from the TFTP server to its RRQ (download requests) if I watch the traffic in wireshark. If I shut down wireshark (running on the TFTP server), the ...
15
votes
6answers
49k views

Testing UDP port connectivity

I am trying to test whether I can get to a particular port on a remote server (both of which I have access to) through UDP. Both servers are internet facing. I am using netcat to have a certain port ...
1
vote
0answers
44 views

TCP and UDP ports usually blocked [closed]

Which are TCP and UDP ports most likely to be blocked? I refer especially to the client edge of the network. To start I guess SMTP (25), SIP (5060) for TCP, Traceroute (33434) for UDP.
3
votes
2answers
2k views

Load Balancing UDP traffic transparently [closed]

Are there any products (preferably open source) that can load balance UDP packets transparently? We need to scale our syslog servers and require the original source IP be kept intact. Alternatively ...