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

2
votes
1answer
1k views

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? ...
2
votes
2answers
358 views

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 ...
2
votes
3answers
4k views

Wireshark won't pick up packets sent from localhost to localhost via network [duplicate]

I'm running on Windows and trying to get Wireshark to pick up my network traffic. It picks up all outbound and inbound traffic fine, except for a client/server I'm running on my local system. As it ...
2
votes
2answers
97 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 ...
2
votes
1answer
83 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 ...
2
votes
2answers
3k 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
1answer
2k views

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 ...
2
votes
2answers
142 views

What is the lowest udp source port for puppet dns queries?

On CentOS 6.4 and 6.3 I have seen puppet regularly use ports below 32768. This is contrary to the setting for kernel-assigned ports according to: cat /proc/sys/net/ipv4/ip_local_port_range 32768 ...
2
votes
1answer
3k 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 ...
2
votes
1answer
451 views

Creating a simple UDP listener [closed]

The situation is this: I'd like to make a hole punching server for a game and I need to listen to UDP traffic. It will run on a Debian Squeeze VPS so I'm pretty flexible as far as possibilities go. ...
2
votes
2answers
931 views

need a live UDP echo Server IP and port

I require to test my UDP program using echo server. I have tested this application in LAN but now I require it to test it in Internet. Is there and globally recognize freely available well known ...
2
votes
1answer
368 views

Block UDP traffic by rate/string-match on Windows 2008

I am administrating a Windows 2008 server (64-bit). It is being subjected to a focused set of DOS attacks where UDP packets are sent to a specific port and contain a specific string. What I need to ...
2
votes
1answer
1k 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 ...
2
votes
2answers
726 views

Netcat, Syslog, UDP, and <134>

Listening with netcat on UDP 514 to syslog data I see that each sent log message is separated by <134>. Does anyone note what <134> is?
2
votes
3answers
3k views

Why isn't my ip helper-address helping?

I have a hub site with a Cisco 2811 and several remote sites, running a mixture of Cisco 851 and 871 routers configured for site-to-site VPN. I am in the process of adding DHCP scopes and DNS zones ...
2
votes
2answers
2k views

Broadcast UDP over VPN

I have OpenVPN configured and have 5 dd-wrt router clients. I would like the machines on those routers to be-able to UDP Broadcast across all 5 networks. I cannot bridge the interfaces(to my ...
2
votes
2answers
246 views

Can IP spoofed traffic get above the transport layer?

I'd like to know whether you could get packets with a spoofed IP address above the transport layer. My thoughts are: TCP: No, as acknowledgements would never get to the original sender if their IP ...
2
votes
2answers
8k views

What is the default TCP window size on Windows Server 2008?

What is the TCP (and UDP) default window size on Windows Server 2008? I think it's 1480 bytes, but I'm not sure. Can it be changed? How?
2
votes
1answer
518 views

Tunnel only one program (UDP & TCP) through another server

I have a windows machine at home and a server with debian installed. I want to tunnel the UDP traffic from one (any only this) program on my windows machine through my server. For tcp traffic this ...
2
votes
2answers
2k views

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 ...
2
votes
1answer
402 views

Tactic to block a UDP spoofing attack

The packets are margin of 200,000 ~ 800,000 per second and UDP spoofed(0 bytes/46bytes) I have a linux deb 6 and windows server 2003 that is taking a hit. Current idea: - Setup a proxy server up ...
2
votes
1answer
533 views

enable large DNS queries on Microsoft 2008 R2 DNS server

When I run the Network analyzer at http://netalyzr.icsi.berkeley.edu/ it reports: The resolver at could not process the following tested types: Medium (~1300B) TXT records Large (~3000B) TXT ...
2
votes
1answer
1k views

Protecting against UDP flood

One of my servers is being flooded with udp packets on random ports. 12:11:54.190442 IP 182.48.38.227.60173 > localhost.51523: UDP, length 1 12:11:54.190447 IP 182.48.38.227.60173 > ...
2
votes
1answer
124 views

UDP Socket bound to one IP?

Say I have two hosts - Using fictitious IPs for this example, say host A has IP 1.1.1.1. host B has two IPs - 2.2.2.2 and 2.2.2.3. If host B is listening on port 8888, and sees a packet come in from ...
2
votes
1answer
771 views

iptables -m string inspecting udp payload only

This is the rule I'm working with: iptables -A QUERY -p udp -m length --length 24:63 -m udp -m string --algo bm --hex-string '|ffffffff|' --from 12 --to 28 -j QUERYLIMIT Is there a way to inspect ...
2
votes
2answers
4k views

UDP traversal through router automatically without router port forwarding?

Everyone knows the router is working like a firewall. Without port forwarding, a connection (no matter TCP or UDP) cannot be initiated from outside of the router. However, if a user initiate a TCP ...
2
votes
1answer
297 views

Set Windows Firewall to Stateless?

Is there a way to "dumb down" the Windows Firewall on Win2003 or Win2008 from stateful to "stateless", and have it only do basic port filtering on the public interface? If not, is there a simple, ...
2
votes
1answer
34 views

tcpreplay throughput on eth0 well below (iperf confirmed) max

I'm trying to replay captured UDP multicast packets at a rate of a couple of hundreds of Mbps, but it maxes out at about 86 Mbps. (For some strange reason, at other times during the day it ...
2
votes
1answer
2k views

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 ...
2
votes
2answers
2k 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 ...
2
votes
2answers
314 views

How can I find out where a UDP connection fails?

I want to setup a VPN server with OpenVPN, so client PCs can access each other like they were in the same physical network. One problem I encountered is, that I cannot connect via UDP. When I change ...
2
votes
1answer
405 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 ...
2
votes
2answers
810 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 ...
2
votes
2answers
880 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 ...
2
votes
1answer
795 views

Adding more than one IP to sip.conf tcpbindaddr and udpbindaddr (Asterisk 1.8)

The defaults in the sample sip.conf under Asterisk1.8 contain udpbindaddr=0.0.0.0 and tcpbindaddr=0.0.0.0. I want to bind the incoming [foo] extension to udp:192.168.1.1/255.255.255.0, the outgoing ...
2
votes
1answer
610 views

KVM virtualized CentOS can send/recieve TCP but not UDP

I've installed CentOS 5 inside KVN on FC12. I've setup a bridged network that works fine. I can ping the virtualized host from any of my other computers and the other way as well. I can also access ...
2
votes
1answer
35 views

How to see log of apps taking specific port over period of time on Windows?

How can I see for specific time period, which app had bound some specific port in Windows? I am auto-starting my app with windows and I am bounding port 1200 as UDP packet receiver, but sometimes my ...
2
votes
2answers
164 views

Load Balancing UDP traffic transparently

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 ...
2
votes
0answers
140 views

Why is qemu issuing a DHCP discover after it receives a DHCP offer

I'm having some trouble seting up network on qemu. I'm trying the easy option (user). The qemu command I run is this: ./qemu-xilinx/arm-softmmu/qemu-system-arm \ -M xilinx-zynq-a9 -m 1024 ...
2
votes
1answer
362 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 ...
2
votes
2answers
500 views

Solaris doesn't know which MAC address to use to send an UDP multicast message

I have a pair of Solaris 10 boxes which are supposed to send multicast UDP packets to a group of hosts. One of them works just fine, whereas the other one does not. The problem with the second ...
2
votes
2answers
385 views

How does SSL VPN (openvpn) connect via UDP?

I need to test whether an OpenVPN Service (ssl-vpn) is listening on a specific IP address and port from a linux box. I'd like to do that with a bash script or some code in python or c/c++ but that's ...
2
votes
0answers
779 views

Forwarding udp ports iptables packets “lost”?

I have a Linux router (Debian 6.x) where i forward some ports to internal services. Some tcp ports (like 80, 22...) are OK. I have one Application listening on port 54277udp. No return is coming from ...
1
vote
2answers
257 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 ...
1
vote
1answer
2k views

Filter incoming traffic to UDP port for pci compliance

It had been recommended for PCI compliance that I filter incoming traffic to UDP port 5353 please can someone advise what are the steps to do this? I am currently using Centos 5.7 64 bit.
1
vote
4answers
2k 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 ...
1
vote
1answer
596 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, ...
1
vote
4answers
108 views

Just one client bound to address and port: does it make a difference broadcast versus unicast in terms of overhead?

Scenario: I am implementing failed over for a network node, so my idea is to make the master node listens on a broadcast ip address and port. If the master node fails, another failover node will ...
1
vote
1answer
144 views

Interactive shell based on SSH and UDP

I've heard from a friend about a client-server application which initializes on top of SSH connection but implements interactive shell over UDP protocol. It is specifically designed for bad quality ...
1
vote
1answer
2k views

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" ...