Question

Difficulty: MediumRouting Concepts and Dynamic Routing Protocols

Match each routing decision concept on the left with its corresponding description in router path selection on the right.

  • Longest Prefix MatchThe primary criteria evaluated first by a router when choosing among multiple destination route entries with different subnet masks.
  • Administrative DistanceThe rating of trustworthiness used to select the preferred routing source when the exact same destination prefix is learned from multiple protocols.
  • MetricThe calculated cost value used by a single dynamic routing protocol to rank candidate paths to a destination network.
  • Next-Hop AddressThe IP address of the adjacent gateway device to which traffic destined for a remote network must be transmitted.

Answer

Longest Prefix Match pairs with the primary criteria evaluated first when choosing among multiple destination route entries with different subnet masks; Administrative Distance pairs with the rating of trustworthiness used to select the preferred routing source for identical prefixes; Metric pairs with the calculated cost value used by a single routing protocol to rank candidate paths; Next-Hop Address pairs with the IP address of the adjacent gateway device.
Each routing concept directly matches its fundamental role in packet forwarding decisions. Longest Prefix Match specifies that the entry with the longest subnet mask is chosen first. Administrative Distance compares trustworthiness across different routing protocols. Metric measures path desirability within a single protocol. Next-Hop Address identifies the immediate next gateway router on the path.

Step-by-Step Solution

1
Identify the precedence rule for routing table lookup.
Longest Prefix Match is applied first before administrative distance or metric are considered.
Routers always prefer the most specific matching route entry for an incoming destination IP address.
2
Differentiate between inter-protocol and intra-protocol path selection criteria.
Administrative Distance breaks ties between different routing protocols for identical prefixes, whereas Metric breaks ties among multiple routes within the same protocol.
Routers need separate mechanisms to rate protocol source trustworthiness versus internal path performance.
3
Define the forwarding component of a routing table entry.
The Next-Hop Address provides the adjacent layer 3 egress point required to build the encapsulation frame.
Packets must be sent to an immediate downstream router interface to move closer to their final destination.

Key Concept

Routing Table Decision Process and Terminology
Estimated Time:1m 30s
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