Trademarks and domain names can be, but are not necessarily, complementary. A domain name can function as a trademark if used as a brand, e.g. if the mark is used in the upper-left banner of a page or in another emphasized way, but not if it is used solely as an “address” akin to a physical street address. So, owning a domain name does not necessarily give the owner trademark rights in the terms comprising the domain name.
Domain names are frequently a source of trademark-related conflicts, though. Registration and use of a domain name in a way that is likely to create consumer confusion with a mark owned by a third party is quite common, and can be addressed in a couple of ways for most generic top-level domain names, like .com and .net and many more. First, the trademark owner could file a lawsuit in federal or state court. Second, the trademark owner can use an administrative dispute proceeding: the Uniform Domain Name Dispute Resolution Policy (“UDRP”). All registrants of generic top-level domains agree to UDRP proceedings as a condition of registration.
To prevail in a UDRP proceeding, the complainant needs to show that it had rights in a mark that predate the current registrant’s ownership of the domain name, that the domain name is “confusingly similar” to the mark, that the registrant has no “rights or legitimate interests” in the domain name, and that the domain name was registered and is being used in good faith. “Bad faith” can be shown in a variety of fact patterns, the most common of which are “pay per click” ads advertising for competitors of the brand owner.