I have a theoretical question about the loopback implementation on a router.
I understand that the idea of a loopback interface is that it is a virtual interface which never goes down due to a physical line or network problem. Loopback interfaces can be used for testing. I also understand that Loopbacks are often used as the source address for various services (NTP, TFTP, FTP, SSH, TACACS, domain lookup, etc.). These services would, by default, use the IP address of the interface by which they exit the router.
What happens if the routers in the networks are trunked and vlan tagged? Is it then still possible to use the loopback interface to perform domain lookup, ftp or curl?