To use bit.ly pro, you need to make a CNAME entry pointing to cname.bit.ly
How does cname.bit.ly have to be configured in order to let this happen?
Updated for a more detailed explanation.
a.domain.com points to c.b.com a.domain.com simply needs a CNAME entry. c.b.com needs to actually serve the request. How should this server be configured to allow this to happen?