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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Decoding TCP packets as RTP in Wireshark

I'm troubleshooting a WebRTC video calling problem in my app and i'm using Wireshark. One end of my video call is a web app running in my browser window and the other end is a Unity based app on an ...
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How to trace UDP blocking for DNS port 53

Recently both of our DNS servers stopped responding to incoming UDP on port 53, tested with dig and it works with TCP. They both have common ISP. Is there any way to traverse route and find out ...
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how to speed up Internet speed via Wireguard connection [closed]

I have a 1000mbps network at home. Doing a speed-test at Cloudflare scores 9xx mbps. I have tried setting up Wireguard in Japan on Vultr, AWS and GC. GC gives me the best average network speed, which ...
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OpenVPN using UDP is terrible slow over cellular networks

I have a weird problem with OpenVPN for around two weeks now. I am running the OpenVPN server on a Virtual Server (German Hoster netcup) on UDP port 1194. Using this setup clients connecting through a ...
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how to proritize UDP port in tc

I have this TC code sudo tc qdisc add dev eth0 root handle 1: prio sudo tc filter add dev eth0 protocol ip parent 1: prio 1 u32 match ip dport xxxx 0xffff flowid 1:1 where XXXX is the port number. ...
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dmesg + UDP: bad checksum. + rhel 7.x

from the dmesg we get very strange lines as [6484420.812643] raid6: using avx2x2 recovery algorithm [6484420.859086] Btrfs loaded [6484426.278636] nr_pdflush_threads exported in /proc is scheduled ...
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iptables: setting specific rules to IP aliases

We run several game servers all using one port with the use of IP Aliasing, the game servers bind to a specific aliased IP that belongs to the main dedicated server. I've setup netplan already and it ...
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Find the process listening on a port (not showing in lsof)

Using Ubuntu 18.04 I want to know which process or kernel function listens on UDP port 38637. I have researched this problem and found similar questions: https://superuser.com/questions/42843/...
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Keep udp connection from the same client after nginx configuration reloaded

I use nginx as udp reverse proxy. Client sends udp messages to specified nginx port and nginx routes these messages to a backend server specified in configuration. From time to time I need to change ...
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How to set Openvpn mtu, given these tcpdump test results?

I have been warned that the maximum tranport unit (mtu) of the cloud server is 1454 bytes. Indeed, I tried two pings and 1426=1454-28(udp header) is the maximum size one packet of UDP can deliver ...
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OVH server DDOS attack protection

I purchased the server on ovh.com. (not gaming, regular) For 3 days now I’ve been trying to set up protection against DDOS flood. Nothing comes out. Support responds once a day and does not give an ...
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How to capture UDP traffic so it can be piped to grep

I'm trying to capture UDP traffic which is being sent as StatsD metrics (on port 8125). The most simple approach I tried is to run nc -ul 8125 which prints the metrics to the terminal...but they are ...
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Client can't discover server (UDP)

I'm discovering network using UDP broadcast like https://stackoverflow.com/a/22853295/13117660. I have tried 4 different options. LAN Server/LAN Client LAN Server/WIFI Client WIFI Server/LAN Client ...
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How to setup nping echo mode to listen on an UDP port?

nping, which is part of nmap, has an echo mode: it runs as a client on one side and as a server on the other side to let you see what packets actually go through. However, I cannot make it listen on ...
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How does TCP over UDP get return packets

How does a server send packets back to the client if there is only a UDP connection, when the client is behind a firewall, and UDP by definition does not maintain a stateful connection. If I had a ...
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1answer
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UDP comunication at the and of a TCP request

I'm learning about network protocols, in particular TCP and UDP. I've written a c++ client that get the HTTPS response of this page 216.58.198.35 (Google), then I've used Wireshark to analyze the ...
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How to send stream from real IP to private IP (My PC IP) using UDP

I am working with a push-to-talk (PTT) application. Where I need to send voice stream from any computer/mobile to server. The server is running under a real IP (203.x.x.x), I can send the stream from ...
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How to set up GELF logging in Docker for Windows

I'm running Windows 10 Pro 1909 (18363.657) and would like to stream the containers stdout to a locally installed log monitor accepting GELF over UDP (it is seq in my case). I have tested my local ...
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SOLVED - OpenVPN and iPTables

Solution: Just had to use NAT 10.8.0.1 Edit: OpenVPN is not working also with iPTables completely clear, so probabily could be an error in the setup. I'm trying to setup an OpenVPN server on my ...
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286 views

Send SOCKS proxy credentials over SSL/TLS

OpenVPN client config file has a socks-proxy rule which allows connecting to a SOCKS proxy before connecting to a VPN. I installed Dante SOCKS proxy but it looks like it does not support SSL/TLS so ...
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TCP NAT forwarding works, UDP doesnt

I am using an Ubuntu Computer as a Router. It has a network connected locally on eth0 and is also connected to the internet with another interface and inside of an OpenVPN. I set up NAT port ...
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Can nginx cache UDP requests?

I have a server in front of several backend servers that act as router using iptables DNAT. As I know, every connection will be tracked by the conntrack module and the count is limited. I have an ...
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What is the meaning of “User” in “User Datagram Protocol” (UDP)? [closed]

Most sources are pretty accurate in the definition of "Datagram" or "Protocol", but where does "User" fit in the whole scheme of things? Is this a user of the protocol itself, is it related to server ...
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How can I make my libvirt/KVM guest see all IPv4/UDP multicast traffic?

I have an issue with IPv4/UDP multicast traffic not being fully visible from within a KVM guest. The guest has a dedicated NIC which is attached using MacVTap. Both the host OS and the OS in the ...
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Windows 10 becoming un-responsive when receiving lots of UDP multi-cast network traffic (but not with unicast traffic)

By coincidence we found that our Windows 10 machines (running version 1607 or 1809) becomes sluggish and/or start stalling when we throw lots of UDP multicast traffic on them. This happens if we send ...
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How can HTTP work over UDP (in the case of Google's QUIC protocol)? [closed]

Here is my understanding of how a client-server HTTP server works. The client creates a TCP socket connection to connect to the server and sends data. The server creates a TCP socket connection to ...
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68 views

Cloning a UDP packet recieved on localhost to another IP

I have a machine A with local ip 192.168.0.199 - I want to clone all udp packets recieved on a local machine and forward to machine A i tried the below in IP tables sudo iptables -A OUTPUT -t nat -p ...
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How to forward UDP traffic on same eth0 interface from one to another port

I am trying to follow some guidelines to forward UDP traffic, but it seems that nothing works. I am having a Syslog server pushing logs to my Logstash instance (yes, EC2) on port 514. As this is a ...
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How to find root cause of throughput decrease and packet loss increase?

Short summary of my issue: How or why can a stable server suddenly start to perform worse for several days, only to later (seemingly automatically) return to normal? I'm doing some performance ...
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61 views

Transparent UDP intermediary for error correction / retransmission

If wanting to use UDP for performance over TCP, is there something which can act as an intermediary on the sender side and receiver side where packets are fed to it and it sends them over UDP but also ...
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2answers
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Why udp has lower throughput than tcp? [duplicate]

I am measuring the tcp and udp throughput by iperf3. I run iperf3 in virtual machines, one as server and the other as client. The VMs are connecting via 10 Gbps link. The results show that tcp get ...
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Server creating UDP routing loop

Our Ubuntu 16.04.6 server is receiving UDP packets from a distant machine (the packets destination address is our server) When the UDP receiver (a simple C program receiving UDP packets and ...
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UDP Hole punching guidance

I am trying to experiment with UDP hole punching to try to connect 2 computers. The 2 computers I am trying to connect are on 2 different Wifi created by the same router. Let me call these computers ...
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iptables matching pattern followed by 4 random values followed by another pattern

I'm trying to create a iptables rule that matches the following pattern in this UDP packet: 0x0000: 0000 030a 0000 0000 0000 0000 0000 0800 ................ 0x0010: 4500 0027 5d30 0000 6c11 232a ...
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Routing TCP packets to a local UDP port

A third party server sends UDP packets to an EC2 instance we've set up and I'm trying to route those packets to my local machine. The client sends these packets to port 8975 To that effect I first ...
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Lost UDP fragments

On my PC I have an issue related to UDP: when snmp bulk request comes and response size is larger than MTU (1500), UDP packet fragmented but only the first part is sent to network. I get a traffic ...
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230 views

syslog udp load balancing and failover with keepalived

I have a simple two host graylog cluster for which i need to load balance udp syslog traffic, I'm using keepalived, floating ip and load balancing work perfectly, but it still directs traffic to all ...
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196 views

sar + get network info from sar

this syntax give the network info on sa1 file sar -n DEV -f /var/log/sa/sa1 how to get the info only from UDP protocol ? we try also sar -n UDP -f /var/log/sa/sa1 Requested activities not ...
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How to filter udp flood on dedicated machine

someone has any technique to prevent UDP floods or somehow filter them? It's being a big issue because it can't be traffic limited, so delaying UDP packets will not work. Please if someone has ...
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Under ddos attack, legit packets increase length also?

I would like to know about packets length, for example, with normal traffic (without DDoS attack) packets length is 20-40, which I believe is normal, once DDoS attack starts packets length goes over ...
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224 views

How do I trigger a client reconnect with OpenVPN?

I am running multiple replicas of OpenVPN server (on a Kubernetes cluster) and have configured clients to reconnect should a server instance go down (with keepalive 10 60) which works fairly well. ...
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Using PHP to create a udp listening post

I have a php application that manipulates database and supplying REST API for clients, it works fine. I was asked to add it capabilities to listen to UDP port, 24/7, and use whatever is submitted ...
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How to start iperf3 server in UDP mode?

I would like to test UDP connectivity with iperf3 but do not know how to start it in UDP server mode. iperf3 -s only opens a TCP socket: root@srv ~# lsof -i -P | grep iperf3 iperf3 21030 ...
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Simple socat UDP6 relay test setup not working

I'd like to use socat as a relay to let two players (both behind firewalls) of my game connect to each other. The game engine uses UDP. Player A will host the game server, player B will join as client,...
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Windows Server Firewall: Block all incoming traffic except from domain members

I want to secure a Remote-Desktop server farm (running on Windows Server 2019). I run multiple servers with different roles (as Active Directory, Connection Broker, RD Gateway, ...). Now I want to ...
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1answer
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Node.js UDP listener inside Docker container reports packets' source IP unreliably

I have a Node.JS application receiving UDP packets, which I have recently moved into a Docker container for easy deployment. The application relies on distinguishing multiple UDP streams based on the ...
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BAD UDP LENGTH > IP PAYLOAD LENGTH

My UDP server program is unable to receive UDP messages from the socket. After checking the PCAP file, I realized that the error is due to: [BAD UDP LENGTH 736 > IP PAYLOAD LENGTH] Len=728 I ...
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1answer
562 views

How to set a port to listen on udp instead of udp6?

I have an application that listen on udp port 1234. I already added the udp/1234 in my firewall and checked if the port is already added to the allowed ports. When I checked if the port is listening ...
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Partially obstructed communication when publishing Docker container on different host port

I have a game server running inside a Docker container that listens on UDP port 1111 (EXPOSE 1111/udp). When I publish this server on the same port on the host (-p 1111:1111/udp) everything works as ...
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81 views

IPTables or alternate solution to block the first attempt to connect then allow further attempts from same IP

I have a unique situation in which a DDOS attack for a certain game is sending realistic player connection packets that seem to perfectly mimic a real player's connection packet. These typically ...

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