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Zorluk: KolayRouter Forwarding Decision Logic

When a router processes an incoming IP packet to make a forwarding decision, it evaluates matching candidate routes using a deterministic precedence hierarchy. Place the following routing decision criteria in the correct order of evaluation from first (1st) to last (4th).

  1. 1Longest prefix match (the route with the most specific matching subnet mask length)
  2. 2Administrative distance (lowest preference value among competing routing sources)
  3. 3Metric (lowest internal path cost within the same routing protocol)
  4. 4Equal-cost load balancing (distributing traffic across tied paths)

Cevap

The correct sequence for router forwarding decision logic is: 1) Longest prefix match, 2) Administrative distance, 3) Metric, and 4) Equal-cost load balancing.
A router evaluates forwarding decisions using a strict hierarchy: first, it determines the longest prefix match (most specific subnet mask matching the destination IP). If multiple routes have the exact same prefix length, it evaluates Administrative Distance to select the route from the most trustworthy source. If multiple routes come from the same routing source with identical prefix lengths, it compares the Metric to pick the path with the lowest cost. Finally, if prefix length, Administrative Distance, and Metric are all equal, the router performs equal-cost load balancing.

Adım Adım Çözüm

1
Evaluate subnet mask specificity for candidate routes matching the destination IP.
Longest prefix match is evaluated first.
The router always prefers the most specific route (longest prefix length) regardless of protocol or AD.
2
Compare routing sources when matching routes have identical prefix lengths.
Administrative Distance (AD) is evaluated second.
Lower AD indicates a more believable/trustworthy routing source (e.g., Static route AD 1 vs OSPF AD 110).
3
Compare route metrics for paths learned via the same routing protocol with identical prefix lengths.
Metric is evaluated third.
Within a single routing protocol, lower metric indicates a lower-cost, more efficient network path.
4
Handle remaining candidate routes where prefix length, AD, and metric are all identical.
Equal-cost load balancing is applied fourth.
When all criteria are tied, the router installs multiple next-hops into the forwarding table for traffic sharing.

Anahtar Kavram

Router Forwarding Precedence Hierarchy
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Konular

Router Forwarding Decision Logic

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