very basic question. All documentation says that loopback interface should be set up on cisco routers since it never goes down, useful for remote configuration ,etc. My question is simple - how to select IP address for it ?? Lets say that I have ISDN router with Dialer interface unnumbered, using loopback's IP. The other interface is connected to Ethernet LAN. How should I pick up IP for loopback interface, is there any guidelines or something ?