A Cisco switch receives an Ethernet frame on a port configured as an 802.1Q trunk link. In what sequential order does the switch process this incoming frame from initial ingress parsing to its final forwarding decision?
- 1Inspect the Ethernet header to detect the presence of an IEEE 802.1Q tag (EtherType 0x8100).
- 2Determine the VLAN association by extracting the 12-bit VLAN ID if tagged, or assigning the port's native VLAN ID if untagged.
- 3Evaluate the assigned VLAN ID against the interface's configured allowed VLAN list.
- 4Forward the frame to appropriate destination ports in that VLAN across the switch fabric, or drop it if the VLAN is disallowed.
Cevap
The correct sequence begins with inspecting the ingress frame header for an 802.1Q tag, assigning the VLAN ID based on tag presence or native VLAN configuration, checking the VLAN against the allowed VLAN list, and finally forwarding or dropping the frame.
When a frame arrives on an 802.1Q trunk interface, the switch performs ingress processing in a strict order: First, it examines the Ethernet header to detect whether an 802.1Q tag (EtherType 0x8100) is present. Second, it determines the internal VLAN ID—reading the 12-bit VLAN ID for tagged frames or mapping untagged frames to the interface's configured native VLAN. Third, it checks whether that VLAN ID is included in the interface's allowed VLAN list. Fourth, if the VLAN is permitted, the switch looks up the MAC table and forwards the frame to destination ports in that VLAN; if the VLAN is disallowed, the frame is dropped.
Adım Adım Çözüm
Anahtar Kavram
802.1Q Ingress Frame Processing Logic
Tahmini Süre:1m 30s