Overview:
A few different types of WAN topology options exist. The concepts behind WAN topology can apply to Layer2 or Layer3 of the OSI model. These are the four types of WAN topology optoins covered on the CCNA exam:
4.4.a Point-to-point
- A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only. These circuits are generally priced based on bandwidth required and distance between the two connected points. Point-to-point links are generally more expensive than shared services such as Frame Relay.
4.4.b Hub and spoke
- Think of a bicycle wheel
- A single core device (the hub) that connects to multiple remote devices (the spokes). In a WAN environment this might be implemented using MPLS, DMVPN, Frame Relay, etc.
4.4.c Full mesh
- Think of a window screen
- All devices are connected to each other.
4.4.d Single vs dual-homed
- Single-homed means a single WAN connection to the internet
- Dual-homed means a router has two independent connections to the internet. This is good for reliability in case one of the connections goes down the other will still be connected.