Administrative distance
General information on “Administrative distance”:
- The AD is a value for ranking routes from most preferred to least preferred
- Every static route as well as routing protocol has a pre-defined AD value which can be modified if needed
- The AD can be between 0 and 255 (infinite)
- If two routing protocols have a route for the same network, only the one with the lower AD will be installed in the routing table
| Route type (protocol) | Default administrative distance |
|---|---|
| Directly connected | 0 |
| Static | 1 |
| EIGRP summary route (only on the summarization router) | 5 |
| eBGP | 20 |
| EIGRP internal | 90 |
| OSPF | 110 |
| IS-IS | 115 |
| IS-IS | 115 |
| RIP | 120 |
| EIGRP external | 170 |
| iBGP | 200 |
| OMP (for VIPTELA/SD-WAN) | 250 |
| Unreachable (not used to pass traffic) | 255 |
“Administrative Distance” CLI configuration commands:
## Modifying the AD of EIGRP (named mode)
Router(config-router-af)# topology base
Router(config-router-af-topology)# distance eigrp <ad-internal> <ad-external>
## Modifying the AD of OSPFv2
Router(config-router)# distance ospf intra-area <ad-ospfv2-intra> inter-area <ad-ospfv2-inter> external <ad-ospfv2-external>
## Modifying the AD of OSPFv3 (configured per AF)
Router(config-router-af)# distance <ad-ospfv3>
## Modifying the AD of BGP (configured per AF)
Router(config-router-af)# distance bgp <ad-ebgp> <ad-ibgp> <ad-local-route>