After connection, even if I do nothing, it will occupy bandwidth

[Variazioni]

With the softether vpn client connected to the VPN, even if I don't do anything, it takes about 7Mbps of bandwidth. And the CPU usage of the vpnserver process is about 25%. The more people connected to the VPN, the higher the usage.
vpnserver is deployed on a centos7 virtual machine, 8cpu 16g ram, the latest rtm version in August 2021 used by both the server and the client.
Since my broadband bandwidth is not large, this thing is very bothering me, does anyone have the same problem as me?
This paragraph is translated from Google Translate, please forgive me if there are any mistakes.

[solo]

All idle SE connections I've ever tested consumed between 1 and 5kbps. SE servers on Windows or Linux.

[Variazioni]

All idle SE connections I've ever tested consumed between 1 and 5kbps. SE servers on Windows or Linux.

Is it possible that this is a network topology problem?
I have tried using Windows and Linux to build a server under the same LAN, and even tried different versions, but the results are the same.
Regardless of whether a Windows client or a Linux client is used, idle connections require 5~10Mbps bandwidth.

[Variazioni]

And I found that the server would send broadcast packets like crazy, I didn't know what was broadcast, and I didn't find any abnormality in the log file.

[Variazioni]

I turned off security nat and dhcp and used the physical router's dhcp service. There are no other special settings.

[solo]

Is it possible that this is a network topology problem?

Yes, a LAN loop and/or broadcast storm could cause it.
Test out your client on a public SE server here https://www.vpngate.net/en/

[Variazioni]

Is it possible that this is a network topology problem?

Yes, a LAN loop and/or broadcast storm could cause it.
Test out your client on a public SE server here https://www.vpngate.net/en/

thank you very much