Improve Layer 2 Down Detection in Network Design with Carrier Ethernet
Question
In a network design using carrier Ethernet, which three mechanisms can be used to improve Layer 2 down detection and thereby reduce routing convergence time? (Choose three.)
Answers
Explanations
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Carrier Ethernet is a popular technology used to provide high-speed connectivity over Ethernet-based networks. In such a network design, it is important to have fast Layer 2 down detection mechanisms to minimize routing convergence time. Here are the three mechanisms that can be used to achieve this goal:
Bidirectional Forwarding Detection (BFD): BFD is a protocol used to detect failures in a network path. It provides fast, low-overhead detection of failures and can be used to detect Layer 2 failures in a carrier Ethernet network. BFD works by sending periodic control packets between two devices and measuring the response time. If the response time exceeds a certain threshold, a failure is detected.
Ethernet Port Debounce Timers: Ethernet port debounce timers can be used to detect physical link failures. When a physical link fails, there can be transient errors that cause the link to flap. Debounce timers can be used to detect these transient errors and prevent false alarms. The debounce timer starts when the link goes down and counts down to zero. If the link comes back up before the timer expires, it is considered a transient error and is ignored. If the timer expires, the link is considered down.
Link-State Tracking: Link-state tracking is a mechanism used to track the operational state of interfaces. In a carrier Ethernet network, link-state tracking can be used to monitor the operational state of Layer 2 interfaces. If a Layer 2 interface goes down, link-state tracking can be used to trigger a routing protocol to update its topology and minimize convergence time.
Other mechanisms that can also be used to reduce routing convergence time include object tracking and fast IGP hello. Object tracking can be used to monitor the state of various network resources, such as interfaces, routing protocols, and IP SLA operations. Fast IGP hello is a feature that enables routers to exchange hello messages at a higher rate, which can reduce the time it takes for the routing protocol to detect a neighbor failure.
