Slow / delayed / long VNC connections

[kamik]

Hello,
I'd like to share my experience with a strange problem - slow / delayed / long VNC connections from master to clients.

Problem:
It takes about 10-15 seconds to complete the VNC connection. Then everything runs smoothly. It is hardware independent.

Environment:
Veyon 4.5.7
OS Windows 10 Pro
HW mix, old Pentium G860+4GB+HDD, i5+8GB+SSD
100 Mbit network

Veyon Config:
(Basic set-up, no control rules)
Authentication method: Logon authentication
Network object directory backend: Ldap
Access control: Grant access to every authenticated user
Authentication keys: none

Debug Log from client (student PC):
https://pastebin.com/LPFu0NtR
Strange delays at 11:21:56.300 and at 11:22:00.879

Solution:
In my case, the problem was missing reverse PTR records in DNS (never used them). VeyonServer.exe (student PC) requested a PTR record of accessing PC (teacher PC), DNS replied NXDOMAIN immediately... then process froze for a few seconds... another DNS request and reply occurred, and then finally a screen appeared.
After filling in the reverse record of master PC to DNS, VNC connects almost immediately.

Not sure why veyon process requests reverse records, I don't use rule "Accessing computer and local computer are at the same location".

Similar topics:
Connection problems - long waiting times
Slow connection on gigabit ethernet
About the slow connecting speed of new version 4.4.0

[tobydox]

Thank you very much for sharing your interesting observations! Indeed Veyon Server performs DNS reverse lookups to log or display machine names instead of IP addresses (e.g. in the tooltip or the connection notifications ("Show notification when an unauthorized access is blocked" or "Show notification on remote connection"). We'll try to change the code such that it resolves hostnames in background to prevent the application from blocking.

[kamik]

@tobydox Thank you for the explanation. I use "Show notification on remote connection".