Administrative Distance in Routing

6 Questions

Which of the following has the least default administrative distance?

Static route to an IP address

Which of the following is a key characteristic of administrative distance?

Configurable

What is the default administrative distance value for OSPF?

110

What happens when multiple routes have the same administrative distance?

Other metrics are used to select the best route

Which of the following use cases involves configuring administrative distance to prioritize specific routes?

Route filtering

What is the default administrative distance value for external EIGRP routes?

170

Study Notes

Administrative Distance

Administrative distance is a value assigned to a route in a routing table to determine its trustworthiness or preference. It is used by routing protocols to select the best route to a destination network.

Key characteristics:

Lowest wins: The route with the lowest administrative distance is preferred.
Default values: Each routing protocol has a default administrative distance value.
Configurable: Administrative distance can be manually configured to influence route selection.

Default administrative distance values:

Connected routes: 0
Static routes: 1
EIGRP: 90 (internal), 170 (external)
OSPF: 110
RIP: 120
BGP: 20 (internal), 200 (external)

Influence on route selection:

A route with a lower administrative distance is preferred over one with a higher value.
If multiple routes have the same administrative distance, other metrics (e.g., metric value, hop count) are used to select the best route.

Use cases:

Route filtering: Use administrative distance to filter out unwanted routes or prefer specific routes.
Route redundancy: Configure administrative distance to ensure redundant routes are used in case of primary route failure.