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350-001 · Question #66

Refer to the exhibit. Assuming that the routing protocol for this network is EIGRP, if the link between R1 and R3 failed, what would R4 receive from R3?

The correct answer is A. R4 would receive an update noting R3's higher cost to reach 172.30.1.0/24. In EIGRP, when a successor route fails and a feasible successor is not available via the failed interface, the router recalculates and advertises an updated metric to downstream neighbors.

Routing Protocols

Question

Refer to the exhibit. Assuming that the routing protocol for this network is EIGRP, if the link between R1 and R3 failed, what would R4 receive from R3?

Exhibit

350-001 question #66 exhibit

Options

  • AR4 would receive an update noting R3's higher cost to reach 172.30.1.0/24.
  • BR4 would not receive any updates or queries, since R3 would simply move to the path through
  • CR4 would receive a query, since R3 would mark 172.30.1.0/24 as active when the link between
  • DR4 would not receive any packets, since R3 is not using the link to R1 to reach 172.30.1.0/24.

How the community answered

(47 responses)
  • A
    64% (30)
  • B
    11% (5)
  • C
    4% (2)
  • D
    21% (10)

Why each option

In EIGRP, when a successor route fails and a feasible successor is not available via the failed interface, the router recalculates and advertises an updated metric to downstream neighbors.

AR4 would receive an update noting R3's higher cost to reach 172.30.1.0/24.Correct

When the R1-R3 link fails, R3 loses its current successor path to 172.30.1.0/24. If R3 has an alternative path (through another neighbor) whose reported distance satisfies the feasibility condition, R3 installs it and sends an update to R4 advertising the new, higher composite metric for that prefix.

BR4 would not receive any updates or queries, since R3 would simply move to the path through

EIGRP does not silently switch paths without notifying downstream neighbors; any change in metric or next-hop triggers an update.

CR4 would receive a query, since R3 would mark 172.30.1.0/24 as active when the link between

R3 would only send a query and mark the route as Active if it had no feasible successor; a query is not the only possible outcome described by the scenario.

DR4 would not receive any packets, since R3 is not using the link to R1 to reach 172.30.1.0/24.

R3 is the router whose link failed, so it must find a new path and propagate changes to R4 rather than staying silent.

Concept tested: EIGRP feasible successor and route update behavior

Source: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html

Topics

#EIGRP#feasible successor#route update#link failure

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