Rusty box underneath?

[Easyrider772]

Hello, new to forum, on my DN-01 and just about every other one I've seen, there is a rusty (exhaust?) box underneath
which seems to contrast with the shiny stainless exhaust. Will these boxes eventually rust through? Has anyone ever replaced
one and are they expensive? Thanks.

 

[spamer80]

Catalytic converter.

The right way to deal with:

Also, it`s the part of exhaust pipes. #8