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Zorluk: ZorL2 Switching Concepts and MAC Table Operation

A Cisco Catalyst switch receives an Ethernet frame on interface FastEthernet0/1. The frame contains a source MAC address that does not currently exist in the MAC address table, and a destination MAC address that is already registered to interface FastEthernet0/4. In what correct sequential order does the switch perform its internal frame processing and forwarding tasks?

  1. 1Receive the Ethernet frame on interface FastEthernet0/1 and inspect the Layer 2 header for source and destination MAC addresses.
  2. 2Check the MAC address table for the source MAC address and create a dynamic entry associating it with FastEthernet0/1.
  3. 3Perform a lookup in the MAC address table using the destination MAC address to identify the associated egress port.
  4. 4Forward the unicast frame exclusively out interface FastEthernet0/4 without flooding.

Cevap

1. Receive the Ethernet frame on interface FastEthernet0/1 and inspect the Layer 2 header for source and destination MAC addresses.
2. Check the MAC address table for the source MAC address and create a dynamic entry associating it with FastEthernet0/1.
3. Perform a lookup in the MAC address table using the destination MAC address to identify the associated egress port.
4. Forward the unicast frame exclusively out interface FastEthernet0/4 without flooding.
When a switch receives a frame, it sequentially executes two main phases: MAC learning followed by frame forwarding. First, it extracts the header information on the ingress port. Second, it inspects the source MAC address; if missing from the MAC address table, it records a dynamic entry associating the source MAC with the receiving port and VLAN. Third, it checks the destination MAC address against its MAC address table. Fourth, because a matching entry exists for FastEthernet0/4, the switch forwards the frame directly out that single interface without flooding.

Adım Adım Çözüm

1
Frame Ingress Inspection
Source and destination MAC address fields are read from the incoming Ethernet frame header.
The switch must inspect the frame header on port FastEthernet0/1 to extract the Layer 2 addressing information.
2
Source MAC Learning
A new entry is added to the MAC address table mapping the source MAC address to interface FastEthernet0/1.
Layer 2 switches learn source MAC addresses upon ingress prior to making any forwarding decisions.
3
Destination Address Table Query
The destination MAC address is matched to existing entry for interface FastEthernet0/4.
The switch inspects its Content Addressable Memory (CAM) table to determine where to direct the frame.
4
Known Unicast Egress Forwarding
The frame is transmitted directly out interface FastEthernet0/4.
Matching a known destination MAC address triggers point-to-point unicast forwarding instead of unknown unicast flooding.

Anahtar Kavram

Layer 2 frame processing pipeline: MAC learning occurs on ingress before destination lookup and forwarding.
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Konular

L2 Switching Concepts and MAC Table Operation

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