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352-001 · Question #22

Refer to the exhibit. Which routes in this network will be installed in the routing table at router E?

The correct answer is C. the OSPF and EIGRP routes. When OSPF and EIGRP advertise routes to different destination prefixes, both routes are installed simultaneously because administrative distance only arbitrates between competing routes to the same prefix.

Layer 3 Control Plane

Question

Refer to the exhibit. Which routes in this network will be installed in the routing table at router E?

Options

  • Athe OSPF route
  • Bthe EIGRP route
  • Cthe OSPF and EIGRP routes
  • Dneither the OSPF nor the EIGRP route

How the community answered

(41 responses)
  • A
    17% (7)
  • B
    2% (1)
  • C
    71% (29)
  • D
    10% (4)

Why each option

When OSPF and EIGRP advertise routes to different destination prefixes, both routes are installed simultaneously because administrative distance only arbitrates between competing routes to the same prefix.

Athe OSPF route

Installing only the OSPF route would occur only if both protocols advertised the same prefix and OSPF somehow had a lower AD than EIGRP, which it does not (OSPF AD 110 vs. EIGRP internal AD 90).

Bthe EIGRP route

EIGRP would win over OSPF for an identical prefix due to its lower administrative distance, but the exhibit shows separate destination networks, so selecting only the EIGRP route would drop reachability to the OSPF-learned destination.

Cthe OSPF and EIGRP routesCorrect

Based on the exhibit topology, the OSPF and EIGRP routes point to distinct destination networks, so there is no competition between them and both are placed in the routing table. Administrative distance (EIGRP internal AD 90, OSPF AD 110) is only consulted when two protocols advertise an identical prefix, which is not the case here.

Dneither the OSPF nor the EIGRP route

Both protocol sessions are functional and advertising valid routes; no configuration failure or reachability issue prevents either route from being installed.

Concept tested: Administrative distance and multi-protocol route installation

Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/15986-admin-distance.html

Topics

#administrative distance#OSPF#EIGRP#routing table selection

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