When would you need this: When you need to configure your router to operate on ADSL line provided by an ISP.
Special Requirements: ADSL WAN interface on the router.
When would you need this: When you need to configure your router to operate on ADSL line provided by an ISP.
Special Requirements: ADSL WAN interface on the router.
When would you need this: When you are creating a WAN link. And also when the other end of a WAN link is NOT a Cisco router. Point-to-Point Protocol can be used in synchronous, asynchoronous, HSSI, and ISDN links.
Special Requirements: None.
When would you need this: When you are using ISDN links between more than two nodes.
Special Requirements: The router should have ISDN interface(s).
When would you need this: When you have ISDN WAN link and you want the router to use it.
Special Requirements: The router should have BRI interface(s).
When would you need this: When you want to perform routing between different VLANs.
Special Requirements: You have to make sure that your router support the frame tagging technology used between the switches.
When would you need this: When you are implementing a routing protocol on a large Internetwork and all the networking devices involved are Cisco devices.
Special Requirements: EIGRP is a Cisco proprietary protocol. So, either all the routers in the Internetwork must be Cisco routers, or the routers should be EIGRP capable.