DHCP server cannot be disabled

Switching of the DHCP server does not work. It still offers IP-addresses.
grafik

Strange , recently switched (with the help of @Andy_Wismer) to a dedicated firewall/gateway and switching of the dhcp server in NS worked for me.
Obviously had to reboot the dhcp clients (or request an new dhcp lease);

Are you sure the dhcp-clients do not use a lease from their own cache?

AFAIK, clients usually tend to request the same address they have (after first release). The server might answer “ok” but even “please use this one instead”, sometimes with a little nudge by the reservation…

MOD: With the lack of feedback changed tag to support .

After additional research I am not able to repeat the problem and I currently think that another DHCP server was running in addition to the NS one. When NS was running it always took precedence over the other, but when it was deactivated the other DHCP server leased similar addresses which ones which NS should issue (resp. the client tried to get its old address from the new server), so it looked like the came from the NS one.

Now everything works and the topic can be considered solved.

Into Windows OS a lot of useful info about the DHCP server can be retrieved via ipconfig.

Scheda Ethernet Ethernet:

   Suffisso DNS specifico per connessione: gallo.local
   Descrizione . . . . . . . . . . . . . : Realtek PCIe GbE Family Controller
   Indirizzo fisico. . . . . . . . . . . : 9C-7B-EF-56-52-27
   DHCP abilitato. . . . . . . . . . . . : Sì
   Configurazione automatica abilitata   : Sì
   Indirizzo IPv4. . . . . . . . . . . . : 192.168.10.55(Preferenziale)
   Subnet mask . . . . . . . . . . . . . : 255.255.255.0
   Lease ottenuto. . . . . . . . . . . . : giovedì 19 agosto 2021 12:19:20
   Scadenza lease . . . . . . . . . . .  : domenica 22 agosto 2021 12:19:19
   Gateway predefinito . . . . . . . . . : 192.168.10.1
   Server DHCP . . . . . . . . . . . . . : 192.168.10.1
   Server DNS . . . . . . . . . . . . .  : 192.168.10.1
   NetBIOS su TCP/IP . . . . . . . . . . : Attivato

(Sorry for the italian output, the OS language of this computer is… Italian)

Server DHCP . . . . . . . . . . . . . : 192.168.10.1
this row tells you which IP address is hosting the DHCP server

Lease ottenuto. . . . . . . . . . . . : giovedì 19 agosto 2021 12:19:20
this row tells you date and time of the lease

You can mix the ip address and arp to get the macaddress of your DHCP-Server host

arp -a |findstr 10.1
  192.168.10.1          bc-cf-4f-77-d7-26     dinamico

then use the MAC address to get what the hell should be the brand of the device. In this case, DHCP server is operated by a Zyxel firewall.

Into windows you can be a bit more specific about options provided by your favourite DHCP server using this tool
https://www.networksecurityhome.com/network_tools/dhcp_discovery/dhcp_discovery.html

And with this one you can try to find if there are more than 1 DHCP server
https://4sysops.com/archives/free-dhcp-find-search-rogue-dhcp-servers/

Last but not least: some DHCP servers are configured to look for any running DHCP server after starting, then kill themselves if any is found. Sometimes this behavior is confusing but… May help you to troubleshoot a bit better your network status.

2 Likes

Yes, “ipconfig /all” was the way I found the problem: that correct IP-Adresss was there, BUT from a wrong DHCP-server.