A. Name squatting is a common problem with DHCP and dynamic DNS wherein one client registers a name with DNS, but that name is actually used by another machine. This makes the original machine no longer accessible. As a solution to this for Windows clients, you have the ability to use ACLs on the DNS records so that once a Windows box registers its host record, another machine cannot overwrite it.
The problem comes with non-Windows machines, which can't use ACLs to protect their DNS records. This is where DHCP Name Protection is used. DHCP Name Protection uses a resource record known as a DHCID, gets stored in DNS by the DHCP server. The DHCID keeps track of which machine originally requested the name. When the DHCP server gets a request by a machine with the same name for an IP address, the DHCP server can look at the DHCID in DNS to check if the machine requesting the name is the original machine that used the name. If it's not the same machine, the record in DNS won't be updated.
More information about DHCID and how it's generated can be found on this site.
Related Reading: