Online services appear to be up and running Call of Duty: Black Ops 2 Status.
Please let us know if you are still unable to connect. If so, specify the platform you are on as well as the connection type (wired/wireless). Also include the NAT type that displays in-game. You may also want to try rebooting your router, modem and system.
If you still need assistance, we're here to help!
Try to power cycle the Internet modem and the router to fix any Internet connectivity issues.
Hope that helps.