Administrative Distance - Cisco ASR 9000 Series Configuration Manual

Administrative Distance

Administrative Distance
An administrative distance is a rating of the trustworthiness of a routing information source. In general, the
higher the value, the lower the trust rating. For information on specifying the administrative distance for BGP,
see the BGP Commands module of the Cisco ASR 9000 Series Aggregation Services Router Routing Command
Reference
Normally, a route can be learned through more than one protocol. Administrative distance is used to discriminate
between routes learned from more than one protocol. The route with the lowest administrative distance is
installed in the IP routing table. By default, BGP uses the administrative distances shown in
Default Administrative Distances, on page
Table 1: BGP Default Administrative Distances
Distance
External
Internal
Local
Distance does not influence the BGP path selection algorithm, but it does influence whether BGP-learned
Note
routes are installed in the IP routing table.
In most cases, when a route is learned through eBGP, it is installed in the IP routing table because of its
distance (20). Sometimes, however, two ASs have an IGP-learned back-door route and an eBGP-learned
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
42
42.
Default Value
20
200
200
Implementing BGP
Table 1: BGP
Function
Applied to routes learned from
eBGP.
Applied to routes learned from
iBGP.
Applied to routes originated by the
router.
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