How to find out why debian server loads the network?

Question

Debian

Good night everyone and Happy New Years.
The problem is the following...
I installed Debian on my nettop. The system is clean, from the installations only the graphical interface and the ssh server.
I tried to connect it to my router both via lan and wlan, but after a while I noticed that the Internet was starting to fall on all computers on the network. I disconnect the server from a network - the Internet at once everywhere works.
Artificially limited the speed in both directions on the server, but to no avail.
How can the problem be tracked? Or is this already a known issue?
Thanks

Answer 1

Install iftop, then look with the iftop command.

Answer 2

tcpdump?

Answer 3

You can also look through nethogs nethogs.sourceforge.net

Answer 4

How can the problem be tracked?

Which problem?

I tried to connect it to my router both via lan and wlan, but after a while I noticed that the Internet was starting to fall on all computers on the network. I disconnect the server from a network - the Internet at once everywhere works.

Specify what the Internet "falls" / "works" means? Pages open / do not open in the browser? Pass / disappear icmp-packets ("pings")? Compare the settings (address, network mask on the interface, default router, DNS servers, arp table, routing table) on the affected computer in "working" and "non-working" Internet conditions.
You can also recommend to study the traffic coming from the nettop (using tcpdump/wireshark). I assume this traffic can be seen on other hosts as well (i.e. is it broadcast or multicast). The current hypothesis is that the source of the problem could be an active DHCP server on your nettop giving out incorrect settings. Another option is that the nettop has a static IP address that conflicts with the one already in use.