Administrator Guide

Table 25. VLAN Defaults
Feature Default
Mode Layer 2 (no IP address is assigned)
Default VLAN ID VLAN 1
Default VLAN
When an Aggregator boots up, all interfaces are up in Layer 2 mode and placed in the default VLAN as untagged interfaces. Only untagged
interfaces can belong to the default VLAN.
By default, VLAN 1 is the default VLAN. To change the default VLAN ID, use the default vlan-id <1–4094> command in
CONFIGURATION mode. You cannot delete the default VLAN.
Port-Based VLANs
Port-based VLANs are a broadcast domain dened by dierent ports or interfaces. In Dell Networking OS, a port-based VLAN can contain
interfaces from dierent stack units within the chassis. Dell Networking OS supports 4094 port-based VLANs.
Port-based VLANs oer increased security for trac, conserve bandwidth, and allow switch segmentation. Interfaces in dierent VLANs
do not communicate with each other, adding some security to the trac on those interfaces. Dierent VLANs can communicate between
each other by means of IP routing. Because trac is only broadcast or ooded to the interfaces within a VLAN, the VLAN conserves
bandwidth. Finally, you can have multiple VLANs congured on one switch, thus segmenting the device
Interfaces within a port-based VLAN must be in Layer 2 mode and can be tagged or untagged in the VLAN ID.
VLANs and Port Tagging
To add an interface to a VLAN, it must be in Layer 2 mode. After you place an interface in Layer 2 mode, it is automatically placed in the
default VLAN. Dell Networking OS supports IEEE 802.1Q tagging at the interface level to lter trac. When you enable tagging, a tag
header is added to the frame after the destination and source MAC addresses. The information that is preserved as the frame moves
through the network. The below gure shows the structure of a frame with a tag header. The VLAN ID is inserted in the tag header.
Figure 50. Tagged Frame Format
The tag header contains some key information used by Dell Networking OS:
• The VLAN protocol identier identies the frame as tagged according to the IEEE 802.1Q specications (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 1518 bytes
specied in the IEEE 802.3 standard. Some devices that are not compliant with IEEE 802.3 may not support the larger frame
size.
354 Interfaces