Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityMedium
A network technician needs to configure a default route on a Cisco router to forward all traffic for unknown destinations to the internet service provider (ISP). The ISP's router has an IP address of 203.0.113.1 on the directly connected link. Which command would correctly configure this default route?
- Aip route default 203.0.113.1
- Bip route 0.0.0.0 0.0.0.0 203.0.113.1
- Cip route 255.255.255.255 255.255.255.255 203.0.113.1
- Dip default-gateway 203.0.113.1
Show answer & explanationAnswer & explanation
Correct answer: B. ip route 0.0.0.0 0.0.0.0 203.0.113.1
In Cisco IOS, a default route is configured using the `ip route` command with a destination network of `0.0.0.0` and a subnet mask of `0.0.0.0`. This signifies 'all networks' and 'all hosts'. The next-hop IP address `203.0.113.1` directs traffic to the ISP's router.
Why the other options are wrong
- A. The `default` keyword is not used directly in this form for `ip route` to define a default static route; it must be `0.0.0.0 0.0.0.0`.
- C. This command would configure a route for a specific host (255.255.255.255), not a default route for all unknown networks.
- D. `ip default-gateway` is used on a Layer 2 switch or a host for its default gateway, not on a Layer 3 router to define a route in its routing table.
Cisco IOS Default Static Route
A default static route in Cisco IOS directs any packets for which there is no more specific route in the routing table to a specified next-hop IP address or outgoing interface.
- Configured using `ip route 0.0.0.0 0.0.0.0`.
- Acts as a 'gateway of last resort'.
- Essential for internet connectivity on edge routers.
Memory trick: When in doubt, send it to 0.0.0.0 to the next-hop out!