A core router receives a packet destined for a remote subnet and must select the best path from multiple overlapping entries in its routing database. Place the decision criteria in the exact sequence the routing logic applies them to determine the single active forwarding path.
- 1Filter matching routing table entries to find the route with the longest prefix length (most specific subnet mask).
- 2Compare the Administrative Distance (AD) values of the remaining matching routes if they originate from different routing sources.
- 3Compare the internal metric (cost) among remaining routes learned from the exact same dynamic routing protocol.
- 4Install the winning path into the Forwarding Information Base (FIB) or initiate Equal-Cost Multi-Path (ECMP) load balancing if metrics are identical.
Cevap
The router first evaluates the longest prefix match to narrow candidate routes. If multiple routes match the same prefix length, it evaluates Administrative Distance to select the most trustworthy protocol. If routes originate from the same protocol with equal AD, it uses the metric to break the tie, and finally installs the path or enables ECMP load balancing.
The proper decision path evaluation sequence starts with Longest Prefix Match (prefix specificity), followed by Administrative Distance (protocol believability), then internal protocol metric (path cost), culminating in forwarding path installation or load balancing.
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Anahtar Kavram
IP Route Selection Decision Process