Tagged Questions

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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2
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2answers
868 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?
0
votes
2answers
811 views

UDP over TCP on vpn connections

For example we have a VPN TCP transport connection through proxy. I wonder how is UDP emulated over this TCP connection? How its unreliable nature is emulated?
3
votes
4answers
2k 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 ...
2
votes
1answer
125 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 ...
0
votes
3answers
169 views

UDP pseudoheader

Is it true that in the UDP header 2 bytes store a checksum for verification purposes by the destination host, and that this checksum is generated from a pseudoheader? If this is true, then why does a ...
1
vote
2answers
9k views

How do you prevent UDP-flood based DDOS attacks on a DNS server? [duplicate]

I'm studying networking at the moment, and it just occurred to me that one can easily forge DNS requests with fake IP addresses (since they use UDP). Since DNS relies on UDP for communication, ...
1
vote
8answers
913 views

Network monitoring solution [closed]

I have a big distributed system I need to monitor. Background: My system is comprised of two servers, concentrating and controlling the system. Each server is connected to a set of devices (some ...
2
votes
1answer
837 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 ...
0
votes
2answers
608 views

Network UDP logger with replay

I need network logger utility with ability to replay the data it collected, for example, I will record incoming data on UDP port 1234 for 10 minutes, record it to file, then replay that data (with ...
-1
votes
2answers
1k 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 ...
1
vote
2answers
1k views

Why are UDP messages from outside the network received but not delivered?

I have an Ubuntu Server 10.04 application I've developed that receives messages over a UDP port. The ultimate purpose of this application is to receive messages sent from workers' 3G modems out in ...
2
votes
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
6answers
799 views

which applications based on UDP?

I hava installed nginx on my localhost, then I copy test.avi to html directory, then i can watch the video by http://localhost/test.avi in browser, i want to know, is the video traffic based on UDP? ...
0
votes
3answers
378 views

Can a network interface be configured to have a default gateway for UDP packets?

It is quite possible that my question may not make a lot of sense. I apologize, but I am not a networking guy, and that's my excuse. To elaborate, WikiPedia defines "Default Gateway" as a node on a ...
0
votes
3answers
635 views

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 ...
0
votes
1answer
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 ...
1
vote
2answers
2k views

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 ...
0
votes
1answer
6k views

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 ...
8
votes
2answers
14k views

listen to UDP data on local port with netcat

netcat -ul -p2115 fails with a usage statement. What am I doing wrong? Thanks!
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
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 ...
0
votes
1answer
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.
1
vote
1answer
6k 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 ...
11
votes
3answers
18k views

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 ...
0
votes
1answer
952 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 ...
1
vote
2answers
3k 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 ...
0
votes
2answers
293 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 ...
0
votes
3answers
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. ...
0
votes
1answer
293 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 ...
1
vote
1answer
323 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 ...
0
votes
2answers
254 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 ...
14
votes
5answers
19k views

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 ...
3
votes
3answers
2k views

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 ...
1
vote
2answers
1k views

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 ...
11
votes
3answers
9k views

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 ...
1
vote
3answers
3k 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 ...
0
votes
1answer
143 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 ...
0
votes
1answer
945 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 ...
0
votes
1answer
1k 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 ...
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 ...
1
vote
2answers
5k views

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 ...
0
votes
1answer
58 views

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?
1
vote
2answers
2k views

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 ...
5
votes
2answers
8k views

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 ...
1
vote
1answer
152 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 ...
10
votes
4answers
1k views

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 ...
4
votes
2answers
7k 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 ...
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 ...
4
votes
2answers
812 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 ...
0
votes
1answer
798 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 ...