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352-001 · Question #246
352-001 Question #246: Real Exam Question with Answer & Explanation
The correct answer is C: The EIGRP dead timers will expire due to the absence of EIGRP traffic.. In a switched multi-access network, when a router shuts down its neighbors retain their own physical links to the switch, so EIGRP must rely on dead timer expiration to detect the lost neighbor.
Question
Three routers in a single broadcast domain are connected by means of a standard Ethernet switch. The only Layer 2 protocol running on this link is Spanning Tree Protocol. The only Layer 3 protocol running on this link is EIGRP, which uses a standard configuration. Then, one of the three routers is manually shut down. How will the other two routers discover the loss of this neighbor?
Options
- AThe line protocol on the remaining two routers will be brought down as soon as the carrier is lost
- BThe switch will bring down the carrier on all ports momentarily to force all the routers connected
- CThe EIGRP dead timers will expire due to the absence of EIGRP traffic.
- DThe switch will send a reverse ARP when the router disconnects from the switch.
Explanation
In a switched multi-access network, when a router shuts down its neighbors retain their own physical links to the switch, so EIGRP must rely on dead timer expiration to detect the lost neighbor.
Common mistakes.
- A. The line protocol on the remaining routers will not go down because their physical connections to the switch are still active - only the port of the downed router loses carrier.
- B. Switches do not bring down carrier on all ports when one device disconnects - each port operates independently and only the affected port loses the signal.
- D. Reverse ARP is used by diskless clients to obtain an IP address and is not a mechanism by which switches notify connected routers of topology changes.
Concept tested. EIGRP neighbor loss detection via dead timer
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