AZ-700 · Question #385
You have an on-premises datacenter named DC1 that contains two routers. You have an Azure subscription. The subscription contains a virtual network named VNet1 and a zone-redundant ExpressRoute…
The correct answer is B. On the routers, configure Bidirectional Forwarding Detection (BFD). The 3-minute failover time is caused by slow link-failure detection using standard BGP keepalive/hold-down timers. BGP by default uses a 90-second keepalive with a 180-second hold timer, meaning it can take up to 3 minutes to detect a peer failure. Bidirectional Forwarding…
Question
You have an on-premises datacenter named DC1 that contains two routers. You have an Azure subscription. The subscription contains a virtual network named VNet1 and a zone-redundant ExpressRoute virtual network gateway named GW1 that uses the ErGw3Az SKU. GW1 is attached to VNet1 DC1 is connected to VNet1 by using an ExpressRoute Standard circuit named Circuit1. The DC1 routers are configured as endpoints for Circuit1. Circuit1 traffic traverses two physical links. During a link outage, the connection takes three minutes to fail over. You need to ensure that failovers between the links take less than one second. What should you do?
Options
- AFor Circuit1, select FastPath.
- BOn the routers, configure Bidirectional Forwarding Detection (BFD).
- CFor GW1, change SKU to UltraPerformance.
- DFor GW1, set Active-active mode to Enabled.
How the community answered
(41 responses)- A7% (3)
- B76% (31)
- C5% (2)
- D12% (5)
Explanation
The 3-minute failover time is caused by slow link-failure detection using standard BGP keepalive/hold-down timers. BGP by default uses a 90-second keepalive with a 180-second hold timer, meaning it can take up to 3 minutes to detect a peer failure. Bidirectional Forwarding Detection (BFD) is a lightweight, fast hello protocol that operates independently of BGP and can detect link failures in milliseconds (typically configurable down to 300ms or less). When BFD is configured on the CE routers and the ExpressRoute gateway supports it (ErGw3Az does support BFD), BGP uses BFD failure notifications to trigger near-instant rerouting, achieving sub-second failover. Option A (FastPath) bypasses the gateway for data-plane traffic but doesn't accelerate failover detection. Option C (changing to UltraPerformance SKU) increases throughput but doesn't improve failover speed. Option D (Active-active mode) improves redundancy at the gateway level but doesn't address the link-failure detection latency on the router side.
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