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Questions tagged [udp]

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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What are TCP Port 5445 and UDP Port 3935 used for on Windows Server 2016?

I'm facing a dilemma, I built 2 physical servers and for some reason for all the IP addresses assigned to that server it's listening on Port 5445 (TCP) and also 3935 (UDP). Applying the same ...
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1answer
49 views

Duplication of UDP traffic to two ports on localhost

I need to redirect incoming UDP traffic to two services listening different UDP ports on localhost. I tried: iptables -t nat -I PREROUTING -p udp -d 10.11.12.13 --dport 22 -j DNAT --to-destination ...
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How to diagnose UDP connectivity issues?

I have an OpenVPN connection which was initially over UDP. After some time I started to have serious hiccups when running ssh inside that tunnel. As seen from inside the tunnel, ssh packets were lost,...
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60 views

Conntrack is blocking UDP NAT

I'm working on an application that should relay udp packets from one host to another according to some rules. It is basically NAT. I negotiate UDP ports with both hosts and after that I need to ...
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77 views

How to troubleshoot UDP packet delay on Windows 10?

I have two computers on a local network. The server, which I cannot modify, is sending UDP packets regularly to the client, which I can modify. The client is running Windows 10 and has up-to-date NIC ...
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29 views

Tracking program that sporadically opens ports

On a Debian server I manage, I have a iptables whitelist firewall. For some reason, one process seems to be sending a bunch of unauthorized packets, but I can't seem to identify which one. [1624382....
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85 views

Why does Erlang runtime (or RabbitMQ) listen on a random UDP port?

After an update to RabbitMQ 3.7.8 and Erlange 21.1 (centOS 6 server) netstat shows that beam.smp is listening on a random UDP port on all interfaces: ~$ sudo netstat -pnul | grep beam udp 0 ...
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UDP bad checksum errors

UDP checksum can not be computed by Hardware virtualization (Intel 82599 SRIOV PCI pass-through, DPDK). UDP bad checksum errors are observed in the TCP dump(pcap) collected after host on the Service ...
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43 views

UDP multicast on a dummy NICs

I have an Ubuntu virtual machine that makes some end-to-end testing of a software. For these tests I need 3 ips in the same subnet. 2 ips should listen for udp multicast (224.0.0.50:4321) and make a ...
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29 views

Iptables udp blocking issue

If I had to block port 144 for udp on eth1 in an active way, for packets with source port 8080, but block it actively so not silently ignore, but to send active signal to the sender of this packet ...
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176 views

IPVS (keepalived) doesn't balance UDP connections

I have two load balancer with Debian 8 and three Graylog server with Debian 9. Every server in my network sends logs via rsyslog to a virtual server configured on the LB. The connection is UDP. The ...
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25 views

Reserving bandwidth in order to reduze packet loss rate

Consider a network, in which one Client is sending UDP packets to a remote server and another Client is uploading a file via FTP to a different remote server. These packets are forwarded to the same ...
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2answers
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Forwarded packets are visible by tcpdump but not received by application

I have 3 machines: A 10.8.0.8/24 B 10.8.0.13/24 10.248.0.34/23 C 10.8.0.40/24 10.248.0.12/23 On A I add a route from A to C using: ip route add 10.248.0.12 via 10.8.0.13. Then I test the ...
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35 views

Google compute engine UDP service only accessible from external IPs

I have a small and simple UDP server that's been working in several hosting places for years. I just created a new vm in the google cloud, a Compute Engine, with linux. Default settings for a small ...
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40 views

What happens when UDP and TCP are sharing a link?

The question that I have is about TCP fairness: Say one Host ist transmitting data via UDP, while a second Host is transmitting data via TCP. Both of these Hosts use the same Ethernet connection. ...
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Packet Loss Analysis of a UDP upload in dependence of shared link capacity

I consider two hosts: Host1 is sending UDP packets (between 1000 and 1500 Bytes) to Host2 and at the same time Host2 is sending UDP packets (also between 1000 and 1500 Bytes) to Host1. The ...
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1answer
39 views

UDP. Sending speed is limited by the minimal Ethernet adapter configuration

I have 1Gbit Ethernet adapter on my computer. And I have the other computer with Ethernet adapter 100Mbit. The both in one LAN and connected through the 1Gbit switch. 1 Test: I try to send from my ...
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69 views

Windows Network Load Balancing Duplicates UDP Packages?

Background I have two Windows Server 2012R2 VMs (each with one NIC) listening on port 514 for Syslog UDP messages, which process and then persist the messages to a database. I tried setting up ...
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1answer
41 views

How do I obtain requests per second and latency per request for a UDP Request

I have an HTTP Api Server that is querying a UDP Server. I used wrk to test the requests per second for the HTTP Api Server and now I want to test the UDP Server requests per second and latency per ...
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2answers
64 views

Multiple IP addresses on a single NIC receiving UDP from different subnets

Sorry if I'm not using the right language for all this, I'm a software developer not a server/network administrator! I've got a Windows machine with a single NIC with multiple IP addresses configured....
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2answers
592 views

Install Basic UDP Server on Ubuntu

I'm doing some code testing and one aspect is I need an active UDP Server. I've tried looking online how to install one and haven't had much luck. My only requirement is a UDP Server which I can ...
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Openvpn - TLS on udp failed handshake

I have openvpn on ubuntu 16.04 to accept connections on tcp 443, but when I setup a second config with port 1194 udp, it's giving me: TLS Error: TLS key negotiation failed to occur within 60 seconds (...
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2answers
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Are DNS queries encrypted?

I wonder if DNS queries are encrypted. If so, can you briefly explain the process as I suppose for an encryption to take place, there should at least be a minimum common ground between two parties (...
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1answer
55 views

How does UDP sockets know which source address to respond to?

I have understood that UDP sockets are fully identified by destination IP and destination port. The IPs are in the IP datagram´s header yes, but when the datagram arrive at its destination, only the ...
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104 views

UDP sendto fails when using specific routing tables

I've got a system with multiple interfaces. I've isolated all of those interfaces from each other using a few sysctl options and routing tables and rules. Each interface has its own routing table ...
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2k views

OpenVPN slow over UDP

I am trying to create a site-to-site connection using OpenVPN. The setup in general is operative: I can reach all servers from every node in each network. The bandwidth within networks is high (>1Gbps)...
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375 views

Is a DDoS possible if the port being attacked is closed?

Let's assume a hypothetical situation in which port 50000 of a machine was being bombarded with UDP packets. However, port 50000 on said machine isn't actually open (i.e. the machine is not listening ...
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1answer
84 views

Iperf2 capture received promiscous mode traffic Not Multicast

I want to capture all traffic in my Iperf server that I listen for promiscously, even if I am not the intended IP. I know you can do this with Multicast addresses, but I do not want to follow that ...
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52 views

Netsh event tracing packet capture shows packets; application not getting them

I have many similar Windows 10 machines running a similar set of applications. A number of applications are multicast UDP listeners. They each have massive socket buffers (they could hold 10 sec+ of ...
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1answer
1k views

netdata ipv4 UDP errors

I've recently installed netdata on an Amazon EC2 debian instance that I have. Netdata is pretty cool, nice charts/graphs, painlessly easy to install (compared to others.) A number of times each day I ...
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1answer
110 views

rsyslog upload limitation?

I use rsyslog to upload logs to my Graylog server /etc/rsyslog.conf: $InputFileName /var/log/apache-error.log $InputFileFacility apache $InputFileTag #apacheError: $InputFileStateFile apache-error $...
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1answer
557 views

Wireshark under Windows: Any way to capture packets before dropped by special filter drivers?

I've got some GigabitEthernet Vision cameras, which use Ethernet to communicate. The protocol is simple UDP, but for performance reasons (high packet throughput causing CPU load) the manufacturer uses ...
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1answer
111 views

Force UDP Loopback over the wire

I am trying to setup a small loopback program in python to send UDP packets from one interface to the other. Without modifying iptables, the kernel will just short circuit any communication and send ...
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369 views

Disable NIC Receive Side Scaling hashing

On a benchmark lab system running Fedora Core 27 I've got Intel X710 10GE cards and 12-core Xeon processors, configured with 12 NIC queues and RX Flow Hashing based on both IP addresses and port ...
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71 views

Bandwidth Control Of UDP packets on a router

As in TCP we have a Congestion control receiver window which negotiates between Sender and receiver ,We dont have such in UDP. So if I were to create some sort of bandwidth control on UDP packets (...
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1k views

Can OpenVPN achieve 100 Mbps?

I have been trying to setup an OpenVPN server for a while. I got maximum 50 Mbps between server and client. My client (Windows 10) is in London (AWS), server (Ubuntu 16.04) in New Jersey (Vultr). ...
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CentOS (with firewalld) - Forward udp (netbios) broadcast

I'm trying to implement a small lab infrastructure with VSphere with multiple LAN, 2 of the LANs are : Work : with employee laptops Trusted : With all my server (except web that is in a separate DMZ)...
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185 views

xinetd: udp service returning just a string

I'm using xinetd to provide a simple service, that basically only needs to return a string value. The service is required to support tcp and udp. The tcp services looks like this, and works as ...
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1answer
9k views

nginx: [emerg] “stream” directive is not allowed here

I have the latest NGINX from ppa installed on Ubuntu 16.04. nginx version: nginx/1.12.1 From my understanding, it should support stream and UDP load balancing. But I get this error message: ...
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2answers
1k views

OpenVPN TCP 443

I'm running an OpenVPN Server Version 2.4.4 on my Ubuntu 16.04.3. The VPN connections work absolutely fine with UDP 1194 but when I try to change to TCP 443 it just won't connect. Im using an apache2, ...
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1answer
613 views

What are all these DGRAM items in NETSTAT?

I am assigned a server that has been sending tons of data ourside and isn't used. So, it is most likely compromised. Nothing really seems to be out of order on the server except, they're miles and ...
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1answer
727 views

UDP broadcast to remote site

I've been trying to find a way to allow a sever in a certain subnet to send UDP broadcasts over multiple subnets. The scenario is this: In network A (192.168.1.0/24) we have a backup server (using ...
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232 views

How to configure RRAS on Windows Server 2012 R2 to forward broadcast UDP packets

I have a server running RRAS on Server 2012 R2. Clients connect using an IKEv2 VPN, and are on the same subnet: 192.168.1.0/24 and 255.255.255.0. The server has a single NIC, and VPN ports are ...
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74 views

How to simulate a property of a symmetric NAT?

For the testing of the STUN/TURN configuration I'd like to block all incoming UDP traffic except for the ports on which I've sent something to the remote server recently. Ports are not known in ...
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1answer
183 views

UDP forwarding not always working

I have a udp forwarding to a VM with the rule iptables -t nat -A PREROUTING -i eth0 -p udp -m udp --dport 42000:42020 -j DNAT --to-destination 192.168.1.2 iptables -t nat -A POSTROUTING -s 192.168.1....
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371 views

OpenVPN works with TCP but not with UDP

I have two sites which I want to connect via an OpenVPN tunnel. I have the setup running using TCP as transport protocol, but as this comes with a performance hit, I want to change this to UDP. But ...
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1answer
163 views

nxlog fails to connect, and never retries

I'm having an issue with nxlog, when trying to connect over network. It seems it is linked with misconfigured network (this is on a virtual machine, within Vagrant) Error message is ERROR couldn't ...
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1answer
576 views

SSH is timing out when connecting through OpenVPN

I have setup OpenVPN server in routing mode. When I try connect via SSH to my VPN server it hangs up at: ssh -i .ssh/mpolitaev_mba mpolitaev@192.168.200.1 -vvv OpenSSH_7.4p1, LibreSSL 2.5.0 debug1: ...
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253 views

UDP traffic loss on all interfaces

I've encountered a problem UDP traffic loss in between two servers. Host A hardware is:Supermicro X11SSL-F v1.01 Intel(R) Xeon(R) CPU E3-1270 v5 @ 3.60GHz 32GiB DIMM DDR4 Synchronous 2400 MHz ...
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3k views

Using OpenVPN behind an NGINX Reverse Proxy using the TCP/UDP Stream Proxying Module

I have been using NGINX as a reverse proxy for my home domain for a little over a year now. The proxy lives in an AWS EC2 instance and delivers traffic to my home IP Address and disguises all of the ...