Uses Of Tagged Vlans - Nokia ESB26 User Manual

17.
based VLAN, BiNOS follows the 802.1Q standard that lets you assign a single switch port to
two or more VLANs.
Tagging VLANs
Tagging is a process that inserts a marker (called a tag) into the Ethernet frame. The tag
contains the identification number of a specific VLAN, called the VLAN ID.
The use of 802.1Q tagged packets may lead to the appearance of packets slightly bigger than
the current IEEE 802.3/Ethernet maximum of 1,518 bytes. This may affect packet error
counters in other devices, and may also lead to connectivity problems if non-802.1Q bridges
or switches are placed in the path. By default all the interfaces in the device belong to VLAN
tag number 1 (the VLAN name is default).
Port Default VLAN
In Port-based VLAN classification within a switch, the VLAN ID associated with an
untagged or priority-tagged frame (i.e., a frame with no tag header, or a frame with a tag
header that carries the null VLAN ID) is determined, based on the Port of arrival of the frame
into the Switch. This classification mechanism requires the association of a specific VLAN
ID, the Port VLAN Identifier, or PVID, with each of the Switch's Ports. The PVID is also
known as the port's default VLAN.
The PVID for a given port provides the VID for untagged and priority-tagged frames received
through that port. The PVID for each port contains a valid VID value, not the value of the null
VLAN ID.
If no PVID value has been explicitly configured for a port, the PVID assumes the value of the
default PVID=1. This will result that even though a port is added to a certain VLAN,
untagged traffic will not flow on that VLAN until the port's default VLAN is set to that
VLAN.
NOTE
A port can be configured for more than one untagged VLAN, but with only one PVID. If a
port is a member of several VLANs, its PVID can be changed with the default vlan
command in Interface Configuration mode, or with the add ports default command in a
specific VLAN Configuration mode.

Uses of Tagged VLANs

Tagging is most commonly used to create VLANs that span switches; an example of this type
of VLAN is shown in Figure 17-1.
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Virtual LANs (VLANs)
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