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Zorluk: KolayRouting Concepts and Dynamic Routing Protocols

When a router receives an IP packet, it compares the destination address against multiple matching entries in its routing table. In what sequence does the router evaluate these routing criteria to select the single best path for forwarding?

  1. 1Longest Prefix Match (selecting the route with the most specific subnet mask)
  2. 2Lowest Administrative Distance (selecting the most believable route source)
  3. 3Lowest Metric (selecting the optimal path cost within the same routing protocol)

Cevap

The correct order of route selection evaluation is: 1. Longest Prefix Match, 2. Lowest Administrative Distance, 3. Lowest Metric.
Routers follow a strict hierarchy to determine the best path. First, the router checks for the longest prefix match to find the most specific network destination. If multiple candidate routes share the exact same prefix length, the router compares administrative distance to select the most reliable routing source. Finally, if routes originate from the same protocol and prefix length, the router uses the metric to break the tie.

Adım Adım Çözüm

1
Evaluate subnet mask specificity
The router selects the entry with the longest network prefix (most specific subnet mask).
Longest prefix match always takes precedence over administrative distance and metrics.
2
Compare administrative distance if prefix lengths are equal
The router selects the route coming from the source with the lower administrative distance.
Administrative distance measures the trustworthiness of the routing protocol or static route source.
3
Compare routing metric if route sources are identical
The router selects the path with the lowest metric value (e.g., hop count, cost, or bandwidth).
Metric is used to compare multiple paths learned within the exact same dynamic routing protocol.

Anahtar Kavram

Route Selection Order of Precedence
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Routing Concepts and Dynamic Routing Protocols

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