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4.1.4. Administrative Distance
Administrative Distance (AD) is a measure of trustworthiness of a routing source. Lower AD = more trusted. Used when multiple routing sources provide routes to the same destination. Only the lowest-AD route is installed; the losing source keeps its route in its own database, so if the winner is withdrawn the next-best route is installed automatically (the principle behind floating static routes).
In show ip route the bracketed pair is [AD/metric]: in O 10.0.0.0/8 [110/20], 110 is OSPF's AD and 20 is the route's metric (for OSPF, the summed interface cost, not a hop count).
| Source | AD |
|---|---|
| Connected | 0 |
| Static | 1 |
| EIGRP summary | 5 |
| eBGP | 20 |
| EIGRP (internal) | 90 |
| OSPF | 110 |
| IS-IS | 115 |
| RIP | 120 |
| EIGRP (external) | 170 |
| iBGP | 200 |
| Unknown | 255 (never used) |
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Written byAlvin Varughese
Founder•20 professional certifications