In fact, the main place where it makes sense to consider changing the administrative distance for a routing protocol is when the same route is distributed by two different protocols. For example, suppose you have an OSPF network that uses EIGRP to distribute routes for dial backup links. When both the primary OSPF link and backup EIGRP link are active, the router will prefer the routes it learns via EIGRP by default because of the lower administrative distance values. This will cause performance problems, since the backup link most likely has lower bandwidth, and it will probably also interfere with dropping the dialup connection because it is actively passing tra...
Adjusting AD for routing protocols
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