Unfortunately the times I see the DHCP server shut down in SBS is when a rogue DHCP server is introduced to the network. Typically this occurs when users bring in a home router to use as a wireless access point or a switch. They often don't realize that DHCP is enabled on these devices.
How do you identify a rogue DHCP server?The most common symptoms of a rogue DHCP server on an SBS network are:
- The DHCP service on the SBS server stops.
- Computers are getting an incorrect IP address or DNS server
How do you find the rogue DHCP server?If you are lucky you are aware of new devices brought into the network. Based on this information you may be able to track down the bad device. However, in most cases, you don't know about new devices. So, what steps can we follow to track this sucker down:
- In the System event log on the SBS server there will be an event generated when the DHCP service is stopped. Event 1053 with the Source DHCP-Server indicates the IP address for the rogue DHCP server.
- Try connecting to the IP address with a web browser. If this is a home router or WAP brought into the office, it will probable have a web site for configuration. At the very least this might help you identify the brand of device and indicate what you physically need to be looking for.
- Try to ping the IP address of the rogue DHCP server. If you are lucky it responds back. Then use arp -a to list the MAC address of that IP address.
- If you have web-managed switches, you can log on to the web site for your switches and identify the port that the MAC address is attached to. That will give you the location of the offending device.
- If you don't have web-managed switches, you can use the MAC address to identify the vendor of the equipment causing the issues. Then at least you know what brand of equipment you are looking for.