VLAN Management
VLANs
185 Cisco Small Business 300 Series Managed Switch Administration Guide
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VLAN Description
Each VLAN is configured with a unique VID (VLAN ID) with a value from 1 to 4094.
A port on a device in a bridged network is a member of a VLAN if it can s end data
to and receive data from the VLAN. A port is an untagged member of a VLAN if all
packets destined for that port into the VLAN have no VLAN tag. A port is a tagged
member of a VLAN if all packets destined for that port into the VLAN have a VLAN
tag. A port can be a member of one untagged VLAN and can be a member of
several tagged VLANs.
A port in VLAN Access mode can be part of only one VLAN. If it is in General or
Trunk mode, the port can be part of one or more VLANs.
VLANs address security and scalability issues. Traffic from a VLAN stays within
the VLAN, and terminates at devices in the VLAN. It also eases network
configuration by logically connecting devices without physically relocating those
devices.
If a frame is VLAN-tagged, a four-byte VLAN tag is added to each Ethernet frame.
The tag contains a VLAN ID between 1 and 4094, and a VLAN Priority Tag (VPT)
between 0 and7. See Quality of Service for det ails ab out VPT.
When a frame enters a VLAN-aware device, it is classified as belonging to a VLAN,
based on the four-byte VLAN tag in the frame.
If there is no VLAN tag in the frame or the frame is priority-tagged only, the frame is
classified to the VLAN based on the PVID (Port VLAN Identifier) configured at the
ingress port where the frame is received.
The frame is discarded at the ingress port if Ingress Filtering is enabled and the
ingress port is not a member of the VLAN to which the packet belongs. A frame is
regarded as priority-tagged only if the VID in its VLAN tag is 0.
Frames belonging to a VLAN remain within the VLAN. This is achieved by sending
or forwarding a frame only to egress ports that are members of the target VLAN.
An egress port may be a tagged or untagged member of a VLAN.
The egress port:
•Adds a VLAN tag to the frame if the egress port is a tagged member of the
target VLAN, and the original frame does not have a VLAN tag.
•Removes the VLAN tag from the frame if the egress port is an untagged
member of the target VLAN, and the original frame has a VLAN tag.