Outgoing traffic restricted to application pool?

All,

I have a multi-tenancy setup in IIS, where each client has an app pool their site operates from, for client separation.  If someone's site reaches out to an external connection (like a cloud service), does this outgoing traffic go out a kind of central/shared way or do the differing app pools provide separation?

If they don't, is there a way to cause that separation so they don't impact each other?

Thanks.