In Griffith's Electrodynamics he states: for a wave guide, considering the walls as perfect conductors we have Et=0 and Bn=0 at the inner walls (considering E and B to be 0 inside the material) Et= is the transverse electric field and Bn is the normal magnetic field.

the first case Et=0 is understandable from the reflection at a conductor, where E_0R=-E_0I and E_0T=0 thus Et=0

also Bn=0 since inside the material B=0

but En is not 0 since there can be free surface charges, which is also conceivable but for the case of Bt we consider it as non 0 since there can be a free surface current. But just few pages earlier, when Griffith just introduced the reflection at a conducting surface, he said that for an ohmic conductor, J=(sigma)E thus surface current is 0 since it would take infinite electric field.

Then why don't we use this same consideration in the case of waveguides? are we using non-ohmic conductors?