White Papers

Table 26. 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 defined by different ports or interfaces. In Dell Networking OS, a port-based VLAN
can contain interfaces from different stack units within the chassis. Dell Networking OS supports 4094 port-based VLANs.
Port-based VLANs offer increased security for traffic, conserve bandwidth, and allow switch segmentation. Interfaces in
different VLANs do not communicate with each other, adding some security to the traffic on those interfaces. Different
VLANs can communicate between each other by means of IP routing. Because traffic is only broadcast or flooded to the
interfaces within a VLAN, the VLAN conserves bandwidth. Finally, you can have multiple VLANs configured 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 filter traffic. 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 figure shows the structure of a frame with a tag header. The
VLAN ID is inserted in the tag header.
Figure 51. Tagged Frame Format
The tag header contains some key information used by Dell Networking OS:
● 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 1518 bytes
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.
Interfaces
339