300-415 Question #94: Real Exam Question with Answer & Explanation

The correct answer is B: prefix-list tracking. A traffic black hole occurs when a VRRP master continues to hold the virtual IP but has lost its upstream transport connectivity, causing traffic to be forwarded to a dead path. Prefix-list tracking solves this by configuring VRRP to monitor specific routes in the routing table.

Router Deployment

Question

A network administrator is configuring VRRP to avoid a traffic black hole when the transport side of the network is down on the master device. What must be configured to get the fastest failover to standby?

Options

Alower timer interval
Bprefix-list tracking
Chigher group ID number
DOMP tracking

Explanation

A traffic black hole occurs when a VRRP master continues to hold the virtual IP but has lost its upstream transport connectivity, causing traffic to be forwarded to a dead path. Prefix-list tracking solves this by configuring VRRP to monitor specific routes in the routing table. When the tracked prefixes (representing transport-side reachability) disappear from the routing table, VRRP immediately decrements the master's priority below the standby's, triggering an instant failover. This is faster than OMP tracking (D), which relies on the overlay control plane convergence and adds delay. Lowering timer intervals (A) reduces VRRP hello/dead timers but does not address detecting transport-side failures. Higher group ID (C) is irrelevant to failover speed. Prefix-list tracking directly ties VRRP master election to local routing table state, enabling the fastest possible detection and failover.

Topics

#VRRP#First Hop Redundancy Protocols#High Availability#Interface Tracking

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