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Difficulty: MediumRouting Table Components

A network administrator is reviewing the output of the 'show ip route' command on a Cisco IOS router. Match each routing table component or source code on the left with its correct functional definition on the right.

  • Administrative DistanceDefines the trustworthiness of the routing information source used when selecting between different routing protocols.
  • MetricIndicates the cost value calculated by a specific routing protocol to select the best path among routes from the same source.
  • Prefix LengthSpecifies the subnet mask bit count used by the router to determine the longest matching prefix during packet forwarding.
  • Source Code 'D'Designates that a route entry was dynamically learned through the EIGRP routing protocol.

Answer

Administrative Distance matches the trustworthiness of the route source; Metric matches the protocol-specific path cost; Prefix Length matches the subnet mask bit count used for longest prefix matching; Source Code 'D' matches routes dynamically learned via EIGRP.
Each field in a Cisco IPv4 routing table entry provides distinct information: Administrative Distance prioritizes between routing protocols; Metric determines the optimal path within a single protocol; Prefix Length defines mask length for longest prefix match logic; and the code 'D' identifies routes learned via EIGRP.

Step-by-Step Solution

1
Identify the definition of Administrative Distance.
Administrative Distance rates the trustworthiness of routing protocol sources.
It allows the router to choose the preferred route source when the same network prefix is advertised by different routing sources.
2
Identify the role of Metric in a routing table entry.
Metric represents path cost calculated by an individual routing protocol.
When multiple candidate paths to a destination exist within the same protocol, the route with the lowest metric value is selected.
3
Determine the function of Prefix Length.
Prefix length denotes the subnet mask bit count and determines match specificity.
Routers evaluate prefix lengths to perform longest prefix matching as the primary criteria during packet lookup.
4
Identify the Cisco IOS routing table source code indicator 'D'.
'D' corresponds to EIGRP-learned routes.
Cisco utilizes 'D' for EIGRP (referencing its DUAL algorithm) because 'E' was historically assigned to EGP.

Key Concept

Routing Table Components and Operational Roles
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Topics

Routing Table Components

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