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Zorluk: OrtaL2 Switching Concepts and MAC Table Operation

A Cisco Catalyst switch receives an Ethernet frame on interface GigabitEthernet0/3 configured in VLAN 15. The frame contains a source MAC address of 0050.56a1.1a01 and a destination MAC address of 0050.56a1.2b02. Upon reviewing its MAC address table, the switch finds that destination 0050.56a1.2b02 is already dynamic mapping to interface GigabitEthernet0/3 in VLAN 15, but there is no entry for source MAC address 0050.56a1.1a01. Which action will the switch perform upon receiving this frame?

  1. The switch records the source MAC address 0050.56a1.1a01 on interface GigabitEthernet0/3 in VLAN 15 and filters (drops) the frame.Cevap
  2. B
    The switch floods the frame out all active interfaces in VLAN 15 except GigabitEthernet0/3 because switches treat same-interface traffic as broadcast domain boundary failures.
  3. C
    The switch forwards the frame back out interface GigabitEthernet0/3 toward the destination device after encapsulating it with a discovery protocol TLV.
  4. D
    The switch drops the frame without updating its MAC address table because the source and destination addresses originate from the same collision domain.

Cevap

The switch records the source MAC address 0050.56a1.1a01 on interface GigabitEthernet0/3 in VLAN 15 and filters (drops) the frame.
When an Ethernet frame reaches a switch port, the switch always performs MAC address learning first by inspecting the frame's source MAC address and updating its MAC address table with the ingress port and VLAN. Next, the switch looks up the destination MAC address to make a forwarding decision. If the destination MAC address is located on the exact same port where the frame entered, the switch determines that the destination host is already on the local collision domain/segment and filters (drops) the frame to avoid sending redundant traffic.

Adım Adım Çözüm

1
Examine ingress frame header and process source MAC address learning
The switch inspects the source MAC address (0050.56a1.1a01) and adds an entry mapping 0050.56a1.1a01 to interface GigabitEthernet0/3 in VLAN 15 in its MAC address table.
Layer 2 switches learn source MAC addresses from all incoming Ethernet frames on the port they arrive on.
2
Lookup destination MAC address in the MAC address table
The destination MAC address (0050.56a1.2b02) is found in the MAC address table and is mapped to interface GigabitEthernet0/3 in VLAN 15.
Switch lookup determines which egress port should be used to reach the target destination.
3
Compare ingress port with target egress port and apply forwarding/filtering logic
Since the target egress port (GigabitEthernet0/3) matches the ingress port (GigabitEthernet0/3), the frame is filtered (dropped).
Devices connected through a hub or shared segment on GigabitEthernet0/3 receive local traffic directly; retransmitting the frame out the same port would create unnecessary collision and traffic overhead.

Anahtar Kavram

Layer 2 Frame Filtering and MAC Address Table Operation
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Konular

L2 Switching Concepts and MAC Table Operation

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