Quanta Cloud Technology QuantaMesh QNOS5, Configuration Manual

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3. Configuring L2 Switching Features
3.1. VLANs
By default, all switchports on the switch are in the same broadcast domain. This means when one host
connected to the switch broadcasts traffic, every device connected to the switch receives that broadcast. All
ports in a broadcast domain also forward multicast and unknown unicast traffic to the connected host.
Large broadcast domains can result in network congestion, and end users might complain that the network is
slow. In addition to latency, large broadcast domains are a greater security risk since all hosts receive all
broadcasts.
Virtual Local Area Networks (VLANs) allow you to divide a broadcast domain into smaller, logical networks.
Like a bridge, a VLAN switch forwards traffic based on the Layer 2 header, which is fast, and like a router, it
partitions the network into logical segments, which provides better administration, security, and
management of multicast traffic.
Network administrators have many reasons for creating logical divisions, such as department or project
membership. Because VLANs enable logical groupings, members do not need to be physically connected to
the same switch or network segment. Some network administrators use VLANs to segregate traffic by type
so that the time-sensitive traffic, like voice traffic, has priority over other traffic, such as data.
Administrators also use VLANs to protect network resources. Traffic sent by authenticated clients might be
assigned to one VLAN, while traffic sent from unauthenticated clients might be assigned to a different VLAN
that allows limited network access.
When one host in a VLAN sends a broadcast, the switch forwards traffic only to other members of that
VLAN. For traffic to go from a host in one VLAN to a host in a different VLAN, the traffic must be forwarded
by a layer 3 device, such as a router. VLANs work across multiple switches, so there is no requirement for the
hosts to be located near each other to participate in the same VLAN.
Note: QNOS software supports VLAN routing. When you configure VLAN routing, the switch acts as a
layer 3 device and can forward traffic between VLANs. For more information, see “VLAN Routing”.
Each VLAN has a unique number, called the VLAN ID. The QNOS supports a configurable VLAN ID range of 2–
4093. A VLAN with VLAN ID 1 is configured on the switch by default. You can associate a name with the VLAN
ID. In a tagged frame, the VLAN is identified by the VLAN ID in the tag. In an untagged frame, the VLAN identifier
is the Port VLAN ID (PVID) specified for the port that received the frame. For information about tagged and
untagged frames, see “VLAN Tagging”.
QNOS supports adding individual ports and Port-channels as VLAN members.
Figure 1 shows an example of a network with three VLANs that are department-based. The file server and
end stations for the department are all members of the same VLAN.