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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UDP sends 6 additional packets in Wireshark

I am sending UDP packets using ttcp to another machine which is connected via a Cisco router. However, when I analyze the packets sent in Wireshark, there is a UDP packet sent before the payload ...
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7k views

Reduce firewall rules by half - one iptables rule for tcp and udp

I have a number of iptables rules on my firewall that look like this: iptables -A zone_lan_forward -p tcp -d 1.2.3.0/24 -j ACCEPT iptables -A zone_lan_forward -p udp -d 1.2.3.0/24 -j ACCEPT Is ...
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1answer
1k 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 ...
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2answers
770 views

TCP vs UDP Error-Checking

I've bounced upon two articles that describe in-depth on how TCP and UDP connections work. However there is some kind of inconsistency. Where one article tells me that UDP does no Error-Checking at ...
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2answers
2k views

Per-packet round-robin load balancing for UDP

I need to load-balance UDP traffic between a number of "realservers" and do it in a truly round-robin fashion. I've started with keepalived, but unexpectedly discovered, that LVS treats UDP traffic as ...
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2answers
4k 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 ...
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56 views

Nat Traversal, peers unable to communicate

I'm currently working on a project that requires NAT traversal but I seem to be running into difficulty. I have the following setup running for testing: R1, Verizon Fios router connected to the ...
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1answer
475 views

Serious Packet Loss on UDP using Amazon EC2

I am using ec2 to host a udp TURN server for SIP purpose. Anyway I get a lot of packet loss during voice call, so I did a udp performance test using iperf util. Result: [ ID] Interval Transfer ...
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1answer
4k views

How do I increase UDP Recv-Q

I have a gigabit connection that is not fully utilized but I am getting packet receiving loss. When I do netstat, it shows the Recv-Q sometimes maxes out at 262656 during heavy traffic. Proto Recv-Q ...
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2answers
174 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 ...
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1answer
402 views

UDP packets dropped

A host sends UDP broadcast, but its UDP packets are not received by any other hosts in the same subnet. However, its TCP traffic with others hosts are OK. I observed this using tcpdump. Could it ...
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1answer
71 views

Trouble with VPN Tunnel

How to direct a UDP Packet through a VPN tunnel? The router in question dose not have any features that would allow a UDP flooding or broadcasting, so for this project I am shooting in the dark, any ...
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1answer
1k views

openvpn tcp or udp (specific situation, reliability-layer collisions)

My question is whether to use TCP of UDP for my openVPN connection. I've set up a simple network for a startup company that allows users from the outside to acces the network via an openvpn server (in ...
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1answer
139 views

Is multicast appropriate for sending a copy of a video chat to a server?

I am creating a p2p video chat app using the libjingle/WebRTC code. I would like to collect a copy of these video conversations on our server for users to watch later - but I don't want to suck up too ...
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0answers
355 views

UDP socket receive buffer size change on RHEL6.3

Our system used to work on RHEL5.3 And the socket receive buffer size is 64k. And that works fine. We can get message size up to 64k on UDP socket. But after system upgrade, it is running on RHEL6.3 ...
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1answer
3k views

Is it possible to duplicate a UDP unicast stream with iptables?

I have a proprietary system which transmit a udp video stream from unit #1 (192.168.1.1) to unit #2 (.1.2). I can't make changes to this system, and I'm trying to clone this udp stream so I can access ...
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2answers
789 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 ...
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2answers
353 views

Countermeasures versus incoming DNS reflection attack

i am currently experiencing a DNS reflection attack towards my server. I am getting a massive amount of answers via UDP from Port 53 that my server has never asked for: 02:53:57.626156 IP (tos ...
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1answer
2k views

Tool for forwarding UDP packets Windows

Windows Server 2008 I use portproxy interface to forward traffic , but I looked into the msdn page and I noticed it doesn't support udp protocol . protocol Specifies the protocol to use. ...
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0answers
117 views

Cannot see an EC2 VPN server from another EC2 instance

I'm using openVPN to connect to one EC2 instance from another. The client cannot see the server, however, despite that servers outside of AWS can see the server and successfully negotiate with it. ...
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2answers
683 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 ...
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1answer
269 views

port forwarding to access services on servers behind NAT

I have some security camera systems in different locations, each location does have internet, the ISP is NATing all the IPs so theres no way to open ports to my systems. My solution was to rent a VPS ...
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3answers
182 views

DDOS protection from ISP side, UDP protocol, whitelist

Is it possible to ignore packets from ISP side which are incoming to my server? Is possible this kind of situation ? : I have white list of IP addresses. I continually update white list and sends it ...
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0answers
1k 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 ...
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1answer
656 views

UDP packets to IP addresses other than specific ones not arriving and not shown in Wireshark

I'm writing a service using UDP, but I can't manage to reply to the client. When sending to the client via the DHCP-assigned IP (192.168.1.143) Wireshark shows no sent packets. The server receives ...
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2answers
472 views

nmap scan only state of port

Is it possible with nmap to check only the state of a port whether- open, closed or filtered and NOT the services behind it? The aim is to speed up scan results. Since UDP scan is also involved it is ...
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1answer
506 views

possible UDP attack on BIND?

hello everyone, i was surprised last month when my EC2 instance (ubuntu precise server), that is supposed to be under the free tier still, accumulated lots of traffic... today, while checking my ...
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2answers
4k views

Problems with MDNS flooding on port 5353 UDP

I am running into a big issue at a small network i manage. This network is an Apple network, with airport extremes, expresses, mac book pro's, imac's, ipads, iphones etc... I went to add something to ...
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2answers
1k views

iptables rules for botnet (UDP flood) protection

I'm currently experiencing a massive UDP attack on my server. I host a couple of gameservers, mainly Tf2, CS:GO, CS 1.6 and CS:Source, and my 1.6 server is being flooded. I tried different rules in ...
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1answer
494 views

UDP Packet Size.. max, ping failing to 3G.. Recalcitrant software vendor

We have a network of 330 clients (Service Vans) connected via 3G to our central office. Currently these clients are connected via a small ruggedized 3G router that establishes the 3G connection and ...
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1answer
799 views

Multicast in private LAN with different subnets

after i read Multicast IP Addresses and Multicast accross the subnets I am confused. Configuration: I have two devices in the same network. They may not be in the same Subnet, but ...
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74 views

Two-way UDP on varying-IP networks

I've heard that on some corporate networks, outbound traffic from the same user can hop around different "from" IPs. Does that break two-way UDP, or do the networks only act that way for TCP? If it ...
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1answer
5k 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" ...
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3answers
6k views

Why is UDP slower than TCP on Ubuntu Server?

I transfer data between two Ubuntu Servers (12.04) via iperf on 1Gb LAN. iperf -s <-> iperf -c <addr> -n2G TCP speed = 925 Mbits/sec iperf -su <-> iperf ...
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1answer
146 views

UDP flooding multiple servers [duplicate]

Possible Duplicate: What are the best techniques for preventing denial of service attacks? What do you suggest? Being UDP flooded as I write to multiple servers in different data centers ...
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1answer
209 views

Can NAT port change dynamically in an active session?

I am facing an issue, having client server application where client application is sending UDP data frequently to server and server redirecting back to the client. But in a few cases I am not getting ...
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1answer
1k views

HTTP, TCP, UDP and connectionless

I am a bit confused with HTTP lately. Some facts are that TCP can operate connection orientated or connectionless, this I understand. TCP though is connection-oriented while UDP is connectionless ...
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1answer
853 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 ...
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1answer
1k views

Too much traffic on UDP suspecting bind miss-configuration

A server generates over 600GB of monthly traffic on UDP port (while http is under 1GB), so I ran tcpdump command and I see many (over 10/second or so) fast dns related commands/traffic that looks like ...
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4answers
120 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 ...
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1answer
769 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. ...
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3answers
11k views

What is the “in-the-wire” size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP ...
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1answer
1k views

How to add a broadcast address to loopback with ifconfig on a OS/X?

I am trying to use ifconfig to turn on broadcast on my loopback interface. It currently reads: lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 As you can see, no broadcast address! ...
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2answers
3k 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 ...
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1answer
3k views

iptables port forwarding for active UDP connections

I am trying to set up port forwarding on UDP from port 12345 to port 54321 using the following: iptables -t nat -A PREROUTING -p udp -i eth0 -d 192.168.0.1 --dport 12345 -j DNAT --to ...
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2answers
773 views

Sonicwall IPS blocking Simple Help direct connection

We host a remote access tool called Simple Help. It allows us to access our clients computers and assist them with problems. I can log into it from my remote workstation, and connect to a clients ...
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2answers
2k views

Many clients on a wireless AP for UDP broadcast packets

I asked this question on StackOverflow and was directed over here, so I'd appreciate any advice. I'm deploying a smartphone application as part of a live music performance that depends on receiving ...
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5answers
28k 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 ...
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3answers
485 views

SNMP (UDP) Proxy

I'm Working in a mid-sized telco, and I'm in charge of network monitoring solutions. We have a custom monitoring system, that is using mostly SNMP to communicate with devices. The problem is that ...
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2answers
313 views

Block packets based on length

Can I block packets (Specifically UDP) that are > X length? I am getting attacked exclusively by UDP packets that are very large in size from a large number of IP Addresses. I have a legitimate use ...