cicuit level proxy

[CISSP_Candidate]

How to understand this discrepency in AIO and Official Guide ...

AIO says circuit-level proxy works at network layer, while the Official Guide says it is session layer.

[Jescoi]

All I know is that first statement is the right one - circuit-level proxies work at network layer.

I cannot imagine what rules can firewall apply at session layer!!

Any other clues?