Caller ID display

Hi all,
We have a strange problem:

We have a set up hunt list to be pointed directly from an inbound route. When incoming call comes in, all the extensions do not have CID displayer but only display as "unknown".

However, if you point the inbound route to an extension directly. It will display the correct CID.

Can anyone please give us some advices / or let us know where to check?

Thank you very much in advance.

Daniel