Port-Based Vlans; Vlans And Port Tagging - Dell Force10 S4810P Configuration Manual

Untagged interfaces must be part of a VLAN. To remove an untagged interface from the Default VLAN,
you must create another VLAN and place the interface into that VLAN. Alternatively, enter the
command, and FTOS removes the interface from the Default VLAN.
switchport
A tagged interface requires an additional step to remove it from Layer 2 mode. Since tagged interfaces can
belong to multiple VLANs, you must remove the tagged interface from all VLANs, using the
command. Only after the interface is untagged and a member of the Default VLAN can you use
interface
the command to remove the interface from Layer 2 mode. For more information, see
no switchport
and Port Tagging.

Port-Based VLANs

Port-based VLANs are a broadcast domain defined by different ports or interfaces. In FTOS, a port-based
VLAN can contain interfaces from different line cards within the chassis. FTOS supports 4094 port-based
VLANs.
Note: E-Series ExaScale platforms support 4094 VLANs with FTOS version 8.2.1.0 and later. Earlier
ExaScale supports 2094 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. FTOS supports IEEE 802.1Q tagging at the interface level
to filter traffic. When tagging is enabled, 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.
illustrates the structure of a frame with a tag header. The VLAN ID is inserted in the tag header.
Figure 53-2. Tagged Frame Format
Ethernet
Preamble Destination
Address
6 octets
The tag header contains some key information used by FTOS:
Source Tag Protocol
Address Header Type
6 octets 4 octets 2 octets
Data Frame
Check
Sequence
45 - 1500 octets 4 octets
no
no tagged
VLANs
Figure 53-2
Virtual LANs (VLAN) | 1055