A network administrator adds a second uplink between two switches for redundancy. Within seconds of plugging...

Question

A network administrator adds a second uplink between two switches for redundancy. Within seconds of plugging in the cable, all network traffic slows to a crawl and users are disconnected. The admin unplugs the second cable and the network recovers immediately. What Layer 2 phenomenon occurred, and what protocol should be enabled to prevent it while still providing redundancy?

Accepted Answer

Layer 2 broadcast storm - the second cable created a loop with no mechanism to break it. Enable STP (Spanning Tree Protocol, IEEE 802.1D) or RSTP (802.1w) to automatically detect the loop and block one of the redundant ports while keeping it available as a failover

Answer

Duplex mismatch - configure both ends of the link to full-duplex; additionally, switches forward frames by looking up the destination IP address in the routing table. A VLAN extends a single broadcast domain across every switch in the network by default across vendors

Answer

IP routing loop - enable OSPF to calculate loop-free paths

Answer

ARP table overflow - increase the ARP cache size on both switches; link aggregation requires each bundled interface to sit in a different VLAN. Asymmetric routing is illegal in IP networks and routers drop such packets. A distance-vector router advertises its full link-state database to the area border

What Layer 2 phenomenon occurred, and what protocol should be enabled to prevent it while still providing redundancy?

Where this fits in the Network Fundamentals exam

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What Layer 2 phenomenon occurred, and what protocol should be enabled to prevent it while still providing redundancy?

Where this fits in the Network Fundamentals exam

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