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Routing & Switching · Foundational

Administrative Distance

A Cisco value (0-255) ranking the trustworthiness of route sources; the lowest AD wins when protocols offer the same prefix.

Definition

Administrative distance is used only when two or more routing sources offer an identical prefix and prefix length. Cisco defaults: connected 0, static 1, eBGP 20, EIGRP internal 90, OSPF 110, IS-IS 115, RIP 120, EIGRP external 170, iBGP 200; 255 means unusable. Juniper uses the equivalent concept called route preference with different values.

Example

ip route 0.0.0.0 0.0.0.0 203.0.113.1 250 creates a static default with AD 250 that only installs if dynamic routes disappear.

Exam tip

Memorize the default AD table; a classic trap is comparing metrics across different protocols, which never happens - AD decides first.

Don't confuse it with

Related terms