Port speed and Wan speed

[JohnTylerPearce]

While reading Cisco documentation, router have a specific WAN speed up to 21 Mbps etc or more depending on router. You also see port speeds of 100Mbps or 1Gbps, but why are Wan speeds limited to far less on most Cisco routers.

[Leo Laohoo]

If a router can support, for example, 21 Mbps, you don't want to have an interface of only 10 Mbps and you'll find router with 100 Mbps interface.

Same goes with routers that can support, for example, 125 Mbps.  The routers will come with 1 Gbps interface instead of 100 Mbps interface.