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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Sending a UDP message to a computer inside a network

Say I have the ip and mac address of a computer inside a network and I wish to send him a UDP message. By initializing the mac and ip addresses of the sent message to the given, when the network ...
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106 views

How to simulate high wire speed ?

I want to test the max speed of my VPN(pptp) server, so I plan to download something from one server by VPN, At first, I think the server need to supply a high speed(30M) for client, who can tell ...
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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 ...
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DNS SERVFAIL and Incorrect Flag only via TCP: Broken DNS Servers?

Is it poor configuration to return the root name servers in the additional section for a CNAME lookup that points to another domain? Particularly the one I'm seeing this with is a CNAME hosted by ...
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listen to UDP data on local port with netcat

netcat -ul -p2115 fails with a usage statement. What am I doing wrong? Thanks!
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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 ...
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3answers
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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 ...
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142 views

UDP in DOS and Windows

I have two computers, one with Windows and another with FreeDOS. I want to generate UDP packets on the Windows PC and receive and view the contents of the package on a computer with FreeDOS.
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3k views

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 ...
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how i can identify which process is making UDP traffic on linux?

my machine is continously making udp dns traffic request. what i need to know is the PID of the process generating this traffic. The normal way in TCP connection is to use netstat/lsof and get the ...
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889 views

How to prioritize openvpn traffic?

I have an openvpn server, with one network interface. VPN traffic is extremely slow. I tried to do traffic control with this configuration (currently): qdisc del dev eth0 root qdisc add dev eth0 root ...
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2answers
2k views

Snoop output: how to display readable packet data on one single line?

I'm getting the same data (UDP packets) from two different sources (on 2 different NICs). I'd like to figure out if one source is "faster" than the other, by comparing the reception timestamps packet ...
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291 views

Make bridge table with UDP packet

Assume that all bridge table was empty (or at least don't have source and destination of my connection ) and want to update their bridge table with my sending packet (when I send packet all bridge ...
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2k views

Why are some UDP packets getting blocked?

In our organization, we have two test machines running Windows XP. While attempting to test a roll-my-own UDP message server, I found that both could receive small messages (under 2k) just fine. ...
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1answer
291 views

Is there a method to send UDP output to one logical NIC such that it gets sent out two physical NICs on different subnets?

I have an application that needs to send UDP multicast data "from" either one or two physical NICs on a single Windows Server 2008 machine. In the two NIC configuration, every datagram needs to be ...
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1answer
297 views

Determine the Ports reserved and what service reserved them in Windows XP/2003

this question is always rise. How can i know what ports are currently reserved in windows XP/2003 and what service had reserved them. for example when i want to install Apache, default port will be ...
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242 views

Problem in creating UDP sockets

Our production server is running PostgreSQL v8.2.3 on Red Hat Enterprise Linux Server release 5 (Tikanga). For some reason, statistics collector in PostgreSQL is not working. Even posted this ...
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5answers
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Linux Kernel not passing through multicast UDP packets

Recently I've set up a new Ubuntu Server 10.04 and noticed my UDP server is no longer able to see any multicast data sent to the interface, even after joining the multicast group. I've got the exact ...
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udp through nat

I've two private networks (each of them behind a typical dsl router). The routers are connected to the WWW. The extern interface of each router have one dynamic IP address. I want to stream data via ...
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UDP Flood/DoS or What?

Basically I am receiving a lot of packets/data with random info on UDP protocol. Packet has header and then a lot of XXXXXXX in it's content. I assume it is UDP flood but it comes from different ...
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Sockets found by lsof but not by netstat

I have an application which is running out of file descriptors, apparently by opening sockets, but I can't find out exactly what these sockets do. These appear in the lsof output as java 9689 ...
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3answers
2k views

Ubuntu Server attack? how to solve?

Something (Someone) is sending out UDP packets sent from our whole ip range. This seems to be multicast DNS. Our server host provided this (Our IP Address is masked with XX): Jun 3 11:02:13 ...
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1answer
140 views

Altq limits not being applied to UDP transfers

I have a OpenBSD server acting as a router/firewall with yhr packet filter ruleset shown below, a linux server, and a linux client. When transferring files (using netcat) by TCP, the limits are ...
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891 views

Iptables REDIRECT + openvpn problem

I want to redirect connection to port 22 to my openvpn binded port, on 60001. Openvpn is running on server on 60001 server:~$ sudo netstat -apn | grep openvpn udp 0 0 67.xx.xx.137:60001 ...
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1answer
916 views

How to relax firewall for UDP connections/ports for a specific IP address?

My server is Red Hat Enterprise Linux Server release 5. iptables version is v1.3.5. I want to allow all UDP connections / port for the IP address 192.168.0.200. This IP address is configured in my ...
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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 ...
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Limit rate of outgoing UDP packets per second

since Teamspeak version 3 sends lots of packets per user and our provider is getting problems with his infrastructure above 20.000 packets per second we have to limit it that our servers are not ...
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Sharepoint Ports

I am installing Sharepoint 2007 and I want users to be able to sign into it from outside. I need to know what ports do I need to open and do I need UDP or TCP or both?
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Is there an encrypted udp based tunnel that doesn't need a tun/tap device?

I am looking for a "application tunneling" solution that behaves a similar to an ssl or ssh tunnel but over UDP. One the client end, OpenVPN provides an network interface. I want the client end to ...
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2answers
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Iptables: “-p udp --state ESTABLISHED”

let's look at these two iptables rules which are often used to allow outgoing DNS: iptables -A OUTPUT -p udp --sport 1024:65535 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A ...
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148 views

What does it mean that most dropped packets have a different incoming and outgoing port?

Over the weekend an internet-facing DI-624 router of mine was e-mailing me logs like crazy for some reason. Normally it's a few a day, but it was about one every few minutes instead. Analyzing the ...
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How common are dropped packets in communications within a data center?

Let's say I have 2 machines in the same data center but not necessarily in the same rack. How common would dropped packets be when sent using UDP between these two machines? I'm asking under the ...
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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 ...
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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 ...
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743 views

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 ...
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1answer
791 views

Windows Vista DHCP bug, arp authorize, isc dhcp, workaround

I am trying to find a workaround for the Windows Vista Force Broadcast bug with ISC DHCP and a Cisco Router. The problem is not windows vista trying to obtain an IP address from us that works fine ...
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21k views

Does HTTPS use TCP or UDP?

Does HTTPS use TCP or UDP?
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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 ...
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What are good host firewall rules to allow UDP multicast?

I have a system with a restrictive firewall that will be participating in UDP multicasting (sending and receiving). What's a good set of rules to make the host's firewall allow this? This is my ...
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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, ...
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Using Clonezilla Server Edition with multiple multicast restore operations

I run a computer refurbishing operation for a local non-profit I am a part of. I have been looking into using Clonezilla to do network-based image-restoration. I am very interested in the multicast ...
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Rewriting UDP packets on Linux

I would like to rewrite the contents/payload of UDP packets as they are received by a machine, on selected reports - before they are passed to the listening application. For example, I would like to ...
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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 ...
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2answers
753 views

bind udp problem

I am using bind 9.6.1 and about 2 days ago I realized that there is a bug at bind for windows platform. when server gets "UDP client handler shutting down due to fatal receive error: host ...
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2answers
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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?
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4answers
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OpenVPN and UDP broadcasts

How can I get this to work? Hours of configuring - and no result. Is that possible at all? P.S. UDP broadcasts are needed by old games for LAN play.
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5answers
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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 ...
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What is the difference between UDP and TCP?

My router has two protocols (and a "both" option) that I can select when setting up port forwarding: UDP and TCP. What is the difference between these two protocols and when would you select one over ...