Cisco CCIE Service Provider Written Exam: Troubleshooting Intermittent Packet Loss and Link Bounces
Question
Users are complaining of intermittent high packet loss for seconds at a time.
The engineer troubleshooting the issue finds that a TenGigE link is bouncing for milliseconds at a time, causing the traffic path to reconverge onto a congested FastEthernet link.
What can the engineer do to prevent service-affecting reconvergence only in the case of momentary link bounces until the link can be repaired?
Answers
Explanations
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A. B. C. D. E.D.
The problem described indicates that the network is experiencing intermittent packet loss due to a TenGigE link bouncing for milliseconds at a time. This is causing the traffic path to reconverge onto a congested FastEthernet link, resulting in service disruption. The question asks what the engineer can do to prevent service-affecting reconvergence until the link can be repaired.
The solution to this problem involves adjusting the carrier-delay timer. The carrier-delay timer is used to control the amount of time a router waits before transitioning from one link to another after detecting a link failure. It is used to avoid unnecessary reconvergence caused by momentary link bounces or flapping.
In this case, the engineer should increase the value of the carrier-delay timer. The carrier-delay up timer controls the amount of time a router waits before transitioning from the failed link to the backup link. By increasing the carrier-delay up timer, the router will wait longer before transitioning to the backup link, which will help to avoid unnecessary reconvergence caused by momentary link bounces.
Disabling keepalives and BFD (Bidirectional Forwarding Detection) are not the correct solutions in this scenario. Keepalives are used to ensure that a connection remains active by periodically sending packets to confirm that the connection is still alive. BFD is a protocol used to detect faults in the forwarding path between two routers. Disabling either of these protocols would not address the underlying issue of intermittent link bouncing.
Decreasing the value of the carrier-delay down timer would also not be the correct solution, as this timer controls the amount of time a router waits before transitioning back to the primary link after it has been restored. Decreasing this timer could result in unnecessary traffic being routed over the primary link, potentially causing congestion and further service disruption.
Therefore, the correct answer is D. Increase the value of the carrier-delay up timer.
