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Difficulty: EasyInterswitch Connectivity and Trunking (802.1Q)

An administrator is configuring an IEEE 802.1Q trunk link between two Cisco Catalyst switches. By default, how does an IEEE 802.1Q trunk process Ethernet frames that belong to the configured native VLAN across the interswitch link?

  1. It forwards frames belonging to the native VLAN untagged without inserting a 4-byte 802.1Q header.Answer
  2. B
    It automatically tags native VLAN frames with a 4-byte 802.1Q header containing VLAN ID 1.
  3. C
    It drops all ingress and egress frames belonging to the native VLAN unless manual VLAN pruning is disabled.
  4. D
    It encapsulates native VLAN frames using legacy ISL tagging prior to transmitting them across the trunk.

Answer

IEEE 802.1Q trunks forward Ethernet frames belonging to the native VLAN untagged without inserting a 4-byte 802.1Q tag header.
Under default IEEE 802.1Q operational mechanics, frames associated with the native VLAN are forwarded across interswitch trunk links in their original Ethernet format without an inserted 4-byte 802.1Q header tag. When the receiving switch accepts an untagged frame on its trunk port, it places that frame into its local native VLAN.

Step-by-Step Solution

1
Identify the standard frame-handling behavior of IEEE 802.1Q trunking for native VLAN traffic.
IEEE 802.1Q specifies that traffic belonging to the designated native VLAN is transmitted across trunk links without a tag.
Transmitting native VLAN frames untagged allows backward compatibility with legacy switches or end-user devices that do not support VLAN tagging.
2
Compare native VLAN frame processing against tagged VLAN frame processing.
Non-native VLAN frames receive a 4-byte 802.1Q tag header, whereas native VLAN frames remain untagged.
The receiving switch inspects incoming frames on a trunk link; any frame lacking an 802.1Q tag is automatically assigned to the trunk port's configured native VLAN.

Key Concept

IEEE 802.1Q Native VLAN Untagged Traffic Handling
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Topics

Interswitch Connectivity and Trunking (802.1Q)

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