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300-410 · Question #71

Refer to the exhibit. An engineer is trying to get 192.168.32.100 forwarded through 10.1.1.1, but it was forwarded through 10.1.1.2. What action forwards the packets through 10.1.1.1? router# show…

The correct answer is D. Configure EIGRP to receive 192.168.32.0 route with equal or longer prefix than /24. To ensure packets for 192.168.32.100 are forwarded via 10.1.1.1, the EIGRP route must be configured with a prefix length that is equal to or longer than the currently preferred /24 RIP route.

Layer 3 Technologies

Question

Refer to the exhibit. An engineer is trying to get 192.168.32.100 forwarded through 10.1.1.1, but it was forwarded through 10.1.1.2. What action forwards the packets through 10.1.1.1? router# show ip route D 192.168.32.0/19 [90/25789217] via 10.1.1.1 R 192.168.32.0/24 [120/4] via 10.1.1.2 O 192.168.32.0/26 [110/229840] via 10.1.1.3

Options

  • AConfigure EIGRP to receive 192.168.32.0 route with lower admin distance.
  • BConfigure EIGRP to receive 192.168.32.0 route with longer prefix than /19.
  • CConfigure EIGRP to receive 192.168.32.0 route with lower metric.
  • DConfigure EIGRP to receive 192.168.32.0 route with equal or longer prefix than /24.

How the community answered

(23 responses)
  • A
    4% (1)
  • B
    4% (1)
  • C
    13% (3)
  • D
    78% (18)

Why each option

To ensure packets for 192.168.32.100 are forwarded via 10.1.1.1, the EIGRP route must be configured with a prefix length that is equal to or longer than the currently preferred /24 RIP route.

AConfigure EIGRP to receive 192.168.32.0 route with lower admin distance.

Lowering EIGRP's administrative distance would only matter if the prefix lengths were equal; longest prefix match takes precedence over administrative distance.

BConfigure EIGRP to receive 192.168.32.0 route with longer prefix than /19.

Configuring an EIGRP route with a prefix longer than `/19` is a step in the right direction, but to specifically beat a `/24` route, it needs to be equal to or longer than `/24`.

CConfigure EIGRP to receive 192.168.32.0 route with lower metric.

Lowering the EIGRP metric is considered only after both prefix length and administrative distance have been evaluated; it would not override the preference for a longer prefix from another protocol.

DConfigure EIGRP to receive 192.168.32.0 route with equal or longer prefix than /24.Correct

Routing decisions prioritize the longest prefix match. Since 192.168.32.100 is currently forwarded via the 10.1.1.2 RIP route (`/24`), which is more specific than the existing EIGRP `/19` route, the EIGRP route must be updated. By configuring EIGRP to receive a route with an equal or longer prefix than `/24` (e.g., `/24`, `/25`, `/26`), it will either become the longest match or, if matching `/24`, be preferred due to EIGRP's lower administrative distance (90 vs. RIP's 120).

Concept tested: Routing table lookup preference (longest prefix match)

Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-4.html

Topics

#Routing Table Lookup#Longest Prefix Match#Administrative Distance#EIGRP

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