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Dell Configuration Guide for the S4048–ON System 9.14.2.6

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VLANs and Port Tagging

To add an interface to a VLAN, the interface must be in Layer 2 mode. After you place an interface in Layer 2 mode, the interface is automatically placed in the Default VLAN.

supports IEEE 802.1Q tagging at the interface level to filter traffic. When you enable tagging, a tag header is added to the frame after the destination and source MAC addresses. That information is preserved as the frame moves through the network. The following example shows the structure of a frame with a tag header. The VLAN ID is inserted in the tag header.
Figure 1. Tagged Frame Format
Illustration of the tagged frame format.
The tag header contains some key information that uses:
  • The VLAN protocol identifier identifies the frame as tagged according to the IEEE 802.1Q specifications (2 bytes).
  • Tag control information (TCI) includes the VLAN ID (2 bytes total). The VLAN ID can have 4,096 values, but two are reserved.
NOTE The insertion of the tag header into the Ethernet frame increases the size of the frame to more than the 1,518 bytes as specified in the IEEE 802.3 standard. Some devices that are not compliant with IEEE 802.3 may not support the larger frame size.

Information contained in the tag header allows the system to prioritize traffic and to forward information to ports associated with a specific VLAN ID. Tagged interfaces can belong to multiple VLANs, while untagged interfaces can belong only to one VLAN.

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