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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Why is it 3-way-handshake and not more?

TCP uses the 3-way-handshake mechanism. I understand how it works pretty well but I wonder why it's not 4, or even 5-way? Is it because that's too much overhead and is not needed?
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How to create UDP proxy using iptables

I have a server running UDP server on port 50000. This server receives updates from clients, and pings back the clients every 5 seconds to the socket they were connected from. Now I want to redirect ...
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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 ...
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1answer
3k views

Iptables ratelimit UDP DOS attacks

Well, I've been a victim of Ddos attacks and I really can't figure out how to avoid it. On some machines it works, while on some it doesn't or probably I'm doing it wrong in some way, Attackers are ...
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1answer
453 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 ...
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270 views

How to sniff udp between two windows applications on the same machine

How do I monitor the duplex udp traffic between two apps on my windows machine.
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1answer
449 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 ...
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1answer
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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 ...
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1k views

Iperf udp test show only 50 % of bandwidth

I test bandwith with iperf. I set up UDP protocol. I'm trying to setup limit from 10 to 100 megabit/s. Until 90 megabit max speed is correct. When I write -b 100m or don't write this speed become ...
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759 views

Https tunnel for carrying TCP and UDP packets

I had an issue with running Openvpn over UDP in my college network. The firewall was dropping UDP connections. As http and https were working fine and assuming that the firewall was inspecting packet ...
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998 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 ...
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753 views

Is there any way to set PPTP on UDP Protocol? [closed]

In our network,many web site has been filtered ,so we should use VPN or Socks ,They reduce any tcp connection speed by dropping random packet (Than post and get on http),So ssh,pptp and ... are so ...
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1answer
364 views

ICMP destination unreachable

I am working on an arch linux machine with ethernet interface eth1. I have created interface eth1:0 using ifconfig and given it a dummy hw address (00:01:02:03:04:05). When I send a UDP packet to a ...
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456 views

Some questions on UDP send receive buffer, and networking

I have two debian servers located on the same subnet. They are connected by a switch. I am aware the UDP is unreliable. Question 1: I assume the link layer is ethernet. And MTU from a standard ...
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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.
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2answers
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How are UDP source ports selected?

I just did a packet capture from my machine and filtered out all the UDP connections. I saw certain connections using what appears to be a randomly generated UDP Source port, and certain connection ...
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Listing TCP/UDP process from an organically grown application

I've been asked to compile a list of TCP/UDP and ports they use for the collection of application that comprise our product for a client who wants the information for their firewall. So I fired up ...
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164 views

Service to temporarily queue UDP packets

I have a service running on a linux box that receives a fairly constant stream of packets via UDP. The occasional loss or corruption of packets associated with using UDP is fine. However, the service ...
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4answers
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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 ...
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791 views

UDP and NATs - is the timeout bidirectional?

Is the timeout for an UDP connection through a NAT reset every time a packet is sent OR received by the client, or are there any (common) implementations that require the client to actively send ...
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440 views

NAT UDP Hole punching beginner's basic Qn

Is there any simple example of UDP-NAT hole punching, capable of hole punching for 2 peers communication via internet? I am trying to do UDP hole punching so that it would be possible to NAT ...
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4answers
107 views

How are UDP datagrams that don't have me as a recipient reaching my server?

I have a bunch of UDP datagrams reaching my server that look like so: The question is, my IP is not 208.69.57.21, (it was 208.69.57.101) so how are those datagrams even being received/logged by my ...
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4answers
210 views

Connect to internet via udp protocol

Is it possible if firewall blocking all http trafic but udp protocol is open connect to internet? because skype use udp protocol to connect and users can use skype. But is technicaly possible to cheat ...
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927 views

How to optimize TCP / IP stack in Linux? [closed]

Currently I noticed there are about 15K open connections to localhost. It is mainly connecting to Memcached. I am clueless where I should start to optimize TCP/IP stack. Memcached support UDP, but ...
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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 ...
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1answer
366 views

Why would a UDP socket perform OK on wifi, but not on a cell network?

Noobish question - I have a perl script running on a linux server which opens UDP port 7015. netstat -ulnp shows: udp 0 0 0.0.0.0:7015 0.0.0.0:* ...
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NetBIOS over TCP/IP with no UDP

Is there a way to run NetBIOS entirely on TCP? I have an environment where UDP is not allowed. I need a way for the machines to talk to each other by name. I thought there might be a way to say that ...
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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 ...
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1answer
132 views

What settings should I modify to tune a Linux server for very small yet very high packet rate UDP receive loads?

I am tuning a server that needs to handle small (average of about 50 bytes) UDP packets. The average packet rate is approximately 100,000 packets/second. The data is very burst and can sometimes burst ...
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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 ...
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258 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 ...
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1answer
96 views

tc: packets filter

I need to drop UDP packets with specific UDP port number) on network interface (say eth0). On my setup the interface eth0 is part of the bridge. is it possible to do it using tc command? if yes, how? ...
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UDP Multicast not working without promisc. Already tried rp_filter=0

I'm having issues with multicast traffic in Ubuntu Maverick. It only appears to work when the card is in promisc mode (i.e. if I set it manually, or use a tool such as tcpdump). Adding multicast ...
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tcpdump strange udp line

I've found a strange line in the tcpdump output. Normally UDP packets are dumped in the following form: timestamp IP srcaddress.port > dstaddress.port: UDP, length packetlength but this is just: ...
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199 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 ...
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shell record UDP stream from a specific address

I'm trying to record an incoming UDP stream (stream the sense that it's a stream of consecutive datagrams). I tried netcat but unfortunately multiple sources send data on the same port address and nc ...
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755 views

Which UDP ports are required to resolve external hosts?

Today I asked my hoster to block all UDP ports except port 53. Due to daily UDP attacks, this was currently the only option to stop flooding my lines. Now since the block is in place, I cannot wget ...
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Block All UDP traffic (to prevent ddos) [duplicate]

I have been receiving countless ddos attacks the last couple of weeks. Just now I caught one while I was running iptraf. Normally 99.9% of the packets used on my server are TCP packages, and not UDP. ...
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UDP Protocol - ICMP Error Generation

I know that UDP has no real error control facilties outside of silent discard of packets failing checksums. Am I correct in thinking that a UDP packet with a TTL=1 reaching a router will generate an ...
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(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 ...
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How can I test Multicast UDP connectivity between two servers?

I have a two servers on the same subnet. I have an application installed which uses Multicast UDP to propagate events between the servers and keep them in sync. This does not seem to be happening, ...
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1answer
268 views

(RFC-791) Application Layer PDU size, guaranteed to pass without fragmentation

I am writing a client-server python application, a part of which is using UDP Multicast to communicate. And my current concern is about fragmentation. RFC 791 (page 24) says: Every internet ...
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502 views

Hosting a UDP Server

How do I host a UDP server for free or cheap? I can't afford to actually buy or rent a physical server. I have a prototype server application written in C#, and I can probably rewrite it in any ...
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4answers
960 views

Unable to receive UDP packets from a link-local address [closed]

I have a program which attempts to contact to an embedded device over UDP. The embedded device has a link-local address only (169.254..); the Linux host has a normal (DHCP, RFC1918) address, managed ...
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792 views

how to enable port 7777

I am initiating file transfer using tcp on openfire server. But I am not able to open the port number 7777, from which I need to send files. I changed the security setting in the admin console panel ...
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1answer
901 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 ...
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Getting UDP traffic statistic between particular hosts on Linux

I need to gather some network statistic to test my server application. I've tried many linux tools, but nothing I've found suits my needs. Basically I want to gather some UDP statistics ...
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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 ...
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1answer
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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 ...
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Causes of UDP Flood

This is part of a mail that I received The IP 69.89.6.235 is attacking our server at 94.23.204.191 and 87.98.168.239.80 with UDP flood. I have a newsletter scripts that I use to send newsletter to a ...