010-151 · Question #56
Which table in a switch must be populated with forwarding information as to reduce Layer 2 flooding in the network?
The correct answer is A. MAC table. A switch's MAC address table (CAM table) must be populated with source MAC-to-port mappings so the switch can make unicast forwarding decisions instead of flooding frames to all ports.
Question
Which table in a switch must be populated with forwarding information as to reduce Layer 2 flooding in the network?
Options
- AMAC table
- Bforwarding table
- CARP table
- Drouting table
How the community answered
(27 responses)- A81% (22)
- B7% (2)
- C4% (1)
- D7% (2)
Why each option
A switch's MAC address table (CAM table) must be populated with source MAC-to-port mappings so the switch can make unicast forwarding decisions instead of flooding frames to all ports.
When a switch receives a frame, it looks up the destination MAC address in its MAC address table to determine the correct egress port. If the table is unpopulated or the destination is unknown, the switch floods the frame out all ports in the VLAN except the ingress port, increasing unnecessary traffic. A fully populated MAC table allows the switch to forward frames only to the correct port, eliminating this flooding behavior.
While 'forwarding table' is a generic term, in Layer 2 switching context the specific table used for unicast flood reduction is the MAC address table, not a separate forwarding table.
The ARP table maps IP addresses to MAC addresses and resides at Layer 3; it is not used by a switch to make Layer 2 forwarding decisions.
The routing table is used by Layer 3 devices for IP-based forwarding decisions and has no role in reducing Layer 2 flooding.
Concept tested: Switch MAC address table and Layer 2 flood reduction
Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9300/software/release/17-1/configuration_guide/lyr2/b_171_lyr2_9300_cg/configuring_mac_address_tables.html
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