Get wrong DHCP Adresse 10.254.254.x

pelikanruban

Hello!

I am not sure where I should start diggin.. or even if it is a Pfsense problem. I have the version 2.4.5 Release p1

I have 1 Pfsense in installed in a location. The IP range that would be the correct one is 10.0.2.0/24
When I try to connect to the Wifi, I also get an 10.0.2.xyz IP-adress, with the correct gateway and so on. But now it is getting strange: When I go around and roam to another access point, and then again back to the other access point, I get an 10.254.254.45 IP adresse (the .45 changes, it could also be .150 or whatever!), with a subnet mask of 255.0.0.0 - but no gateway!

The only thing I get again a 10.0.2.x IP adress is to make an ipconfig /release and then /renew. Then it is okay again till the time I roam to another access point.

I thougt maybe it is a bug from Pfsense that I get this strange behavior, but, i recognized this problem at a different location where pfsense is installed as well! The Pfsense version on the other location is 2.4.4 release p3

The problems started out of nowehere about 3 weeks ago, after working 6 months without any problems. It was a power outage there, but I cannot further isolate it.

After some googleing, It told me that there could maybe a Rogue Dhcp server - but I wonder AT TWO LOCATIONS?

Hope someone could help me...

Thank you!
pelikan

EDIT: I have also a different VLAN, with another 172.16.0.0/16 range. In this VLAN I absolutely do not face any problems...

KOM

@pelikanruban It's simple to check. Turn off DHCP on pfSense and then try to renew. If you get a lease, it isn't pfSense.

AndyRH

If you have a Windows client ipconfig /all will give the IP of the DHCP server.

pelikanruban

KOM, AndyRH thank you very much!!! each of your tips was gold for me. first i disabled dhcp on pfsense, then i immediately got a 10.254.254.x ip adress, and then with ipconfig /all it showed me the ip 10.254.254.254 of the dhcp server. i HTTPed on this adress. it was a controller for a lightning control that is installed in each of the locations. i would have never thougt of that device...

thank you very much!

mr.rosh

pfsense shoould have a mechanism as such to detect other DHCP servers in the same ip range, and raise an alert. interestingly enough my cisco meraki switch told me of such via an email alert.

JKnott

@mr-rosh

Does it actually detect servers? Or just duplicate addresses? DHCP is designed to have multiple servers on a network.

AndyRH

Having an option for pfSense to probe for other DHCP servers would be a nice addition.
All it would have to do is make a request on networks that pfSense has a DHCP range defined and report back if there is an answer other than itself.

JKnott

@andyrh

Actually, duplicate address detection is supposed to be used. There's nothing wrong with multiple DHCP servers on the same network. The client does the discovery and works with the first server to respond. Of course, the address range should be divided among servers.

JKnott

@andyrh said in Get wrong DHCP Adresse 10.254.254.x:

Having an option for pfSense to probe for other DHCP servers would be a nice addition.

From RFC 2131:

 o A DHCP client must be prepared to receive multiple responses
    to a request for configuration parameters.  Some installations
    may include multiple, overlapping DHCP servers to enhance
    reliability and increase performance.

AndyRH

I think the point was missed. It would be nice as an option. pfSense being used as the DHCP server implies a small site and a site that would not function very well if pfSense is down. I would think most people running small sites want uncomplicated lives and 2 DHCP servers is not uncomplicated.