Well it was a District Case, but I think it's accurate to say it applies against the Federal Government. Later cases will rule on whether is applies against the State governments and their lower level governments.
There is a Chicago case winding it's way to the Supreme Court now. Chicago's ban is similar enough to DC's that the only issue should be applicability to the states. From the NRA-ILA
Two-thirds of the nation’s attorneys general have filed an amicus brief asking the U.S. Supreme Court to grant certiorari in the case of NRA v. Chicago and hold that the Second Amendment applies to state and local governments through the Due Process Clause of the Fourteenth Amendment
...
California attorney general Edmund G. Brown Jr. is filing a separate brief arguing that the Supreme Court should take up NRA’s appeal and hold that the Second Amendment is incorporated against the States.
California? I think I'll go now before I faint dead away. :)
Of course this "through the due process clause" is so much Bovine Scat. The record clearly shows that the 14th amendment's authors' purpose was to apply the protections of the first 8 amendments, against the states through the "privileges and immunities clause.