Which DHCP server is primary?

the active server
When using hot standby mode one server is the active server and the other is a standby. The active server is the primary server and handles all DHCP requests. If the active server goes down the standby server takes over the DHCP requests.

Can two computers share one IP address?

As I understand it, two computers cannot have the same public (external) IP address unless they are connected via the same router. If they are connected via the same router, then they can have (share) the same public IP address yet have different private (local) IP addresses.

Is it possible to have two DHCP servers on the same server?

Normally, you should not have two DHCP responding for the same gateway (especially when servers are not on the same site, but this is also true when you have different scopes on a same server). You could try IPCONFIG /RENEW command to force the computer to empty its cache and try to get an address from the correct DHCP server

What is a DHCP server and how does it work?

A DHCP server is responsible for allocating IP address and other information to requesting clients. The DHCP server is configured with a range of IP addresses that it can assign and also with other settings like DNS servers, default gateway addresses etc.

Why does my PC have a different IP address?

It’s most likely the PC has picked up a different IP address from the DHCP server, mostly after the one it had was reissued to another device. If you have a reasonably short lease, or the device was not connected for some time, this is possible.

How to tell if multiple network cards have the same IP?

If you have multiple network cards and you mannually configure the metrics (as windows usually does automatically), do an ipconfig and you’ll see that both network cards received an IP from the DHCP server (if they are configured for DHCP, otherwise they’ll use the statically assigned IP).