> Why do the routers involve themselves at the transport layer? Can't they just route IP packets and leave the transport alone? Because they have to do NAT, at

> Why do the routers involve themselves at the transport layer? Can't they just route IP packets and leave the transport alone? Because they have to do NAT, at least on IPv4. > Firewalls -- whose firewalls are we talking about here? If a client (say, home user) tries to initiate an SCTP connection to a server somewhere, what step will fail? Because the connection tracking that's needed to even recognize whether a packets belongs to an outbound or an inbound connection needs to understand the protocol.