A core router learns two separate routes to the destination network 192.168.50.0/24 from t… — CompTIA Network+

A core router learns two separate routes to the destination network $192.168.50.0/24$ from two different dynamic routing protocols. The first route is learned via Internal EIGRP with an Administrative Distance (AD) of $90$ and a metric cost of $2,176,000$ . The second route is learned via OSPF with an Administrative Distance (AD) of $110$ and a cost metric of $20$ . Assuming default settings, which route will the router install into its Routing Information Base (RIB) for traffic destined to $192.168.50.0/24$ ?

The EIGRP route, because lower Administrative Distance takes precedence over protocol metrics when comparing routes from different routing sources.Cevap
B
The OSPF route, because a metric value of $20$ is lower than the EIGRP metric of $2,176,000$ .
C
Both routes simultaneously, distributing traffic using equal-cost multi-path (ECMP) load balancing.
D
Neither route, because dynamic routes require a higher-priority floating static route to be active in order to install entries into the RIB.

Cevap

The EIGRP route is installed because lower Administrative Distance takes precedence over protocol metrics when evaluating routes from different sources.

When a router receives multiple routes for the exact same network prefix from different routing protocols, it uses Administrative Distance (AD) to measure administrative trustworthiness. Internal EIGRP defaults to an AD of 90, whereas OSPF defaults to an AD of 110. Because 90 is lower than 110, the router selects the EIGRP path to populate the routing table. Metric comparisons are only performed between paths learned from the exact same dynamic routing protocol.

Adım Adım Çözüm

Evaluate destination prefix matching.

Both routes target the exact same prefix length (

192.168.50.0/24

Longest prefix match rule applies first, but since the subnet masks are identical, the router proceeds to compare routing sources.

Compare Administrative Distance (AD) values between EIGRP and OSPF.

Internal EIGRP has an AD of

90

, while OSPF has an AD of

110

Administrative Distance indicates the trustworthiness of a routing source. Lower values indicate higher believability.

Select the route for RIB installation.

The route with AD

90

(EIGRP) is selected and installed into the routing table.

Because EIGRP has a lower AD than OSPF, the OSPF route is discarded from RIB consideration, making protocol metrics irrelevant during inter-protocol path selection.

Anahtar Kavram

Administrative Distance vs. Routing Metric in Path Selection

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Adım Adım Çözüm

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