In the context of network routing, administrative distance (AD) is a value used by routers to select the best route when there are several different routes to the same destination from two or more routing protocols.

Administrative distance is intended to determine the credibility or preference of a source of routing information. A lower number indicates greater credibility.

For Border Gateway Protocol (BGP), which includes both Interior BGP (iBGP) and Exterior BGP (eBGP), the default administrative distances are as follows:

• eBGP (Outside BGP): It has an administrative distance of 20. This reflects high credibility, since eBGP routes come directly from other autonomous systems through direct connections, generally considered reliable and crucial for routing between different autonomous systems.
• iBGP (Inside BGP): It has an administrative distance of 200. The higher distance compared to eBGP indicates lower credibility for routes coming from within the same autonomous system via iBGP, especially since iBGP does not change the hop count and relies on other internal routing protocols to Provide up-to-date information on network topology.

These administrative distance values ​​allow routers to give preference to eBGP routes over iBGP when both options are available, thus favoring routes that come directly from other autonomous systems.