Monday, December 7, 2015

Setting untagged port-based and Tagged VLANs

Setting untagged port-based and Tagged VLANs
This section provides a brief description of VLANs and explains how to display, create, and modify port-based and tagged Virtual LANs which are more commonly known as VLANs. See the following sections:
For additional information about VLANs, see the following chapters in the AlliedWare Plus Management Software Command Line Interface User’s Guide:
■ Port-based and Tagged VLANs
■ Port-based and Tagged VLAN Commands


A VLAN is a group of ports that form a logical Ethernet segment on an Ethernet switch. The ports of a VLAN form an independent traffic domain in which the traffic generated by the nodes remains within the VLAN.
VLANs let you segment your network through the switch’s management software so that you can group nodes with related functions into their own separate, logical LAN segments. These VLAN groupings can be based on similar data needs or security requirements. For example, you could create separate VLANs for the different departments in your company, such as one for Sales and another for Accounting. Both port-based and tagged VLANs are supported in the web interface.

Port-based VLANs

A port-based VLAN is a group of ports on a Gigabit Ethernet Switch that form a logical Ethernet segment. Each port of a port-based VLAN can belong to only one VLAN at a time. A port-based VLAN can have as many or as few ports as needed. The VLAN can consist of all the ports on an Ethernet switch, or just a few ports. In addition, a port-based VLAN can span switches and consist of ports from multiple Ethernet switches.
Ports in a port-based VLAN are referred to as untagged ports and the frames received on the ports as untagged frames. The names derive from the fact that the frames received on a port do not contain any information that indicates VLAN membership, and that VLAN membership is determined solely by a port’s PVID.

Port VLAN Identifier

Each port in a port-based VLAN must have a port VLAN identifier (PVID). The switch associates a frame to a port-based VLAN by the PVID assigned to a port on which a frame is received, and forwards a frame only to those ports with the same PVID. Consequently, all ports of a port-based VLAN must have the same PVID. In addition, the PVID of the ports in
a VLAN must match the VLAN’s VID.
For example, if you create a port-based VLAN on the switch and assign it the VID 5, the PVID for each port in the VLAN needs to be assigned the value of 5.

Tagged VLANs

The second type of VLAN is the tagged VLAN. VLAN membership in a tagged VLAN is determined by information within the frames that are received on a port. This differs from a port-based VLAN, where the PVIDs assigned to the ports determine VLAN membership.
The VLAN information within an Ethernet frame is referred to as a tag or tagged header. A tag, which follows the source and destination addresses in a frame, contains the VID of the VLAN to which the frame belongs (IEEE 802.3ac standard). This number uniquely identifies each VLAN in a network.
When the switch receives a frame with a VLAN tag, referred to as a tagged frame, the switch forwards the frame only to those ports that share the same VID.
A port that receives or transmits tagged frames is referred to as a tagged port. Any network device connected to a tagged port must be IEEE 802.1Q-compliant. This is the standard that outlines the requirements and standards for tagging. The device must be able to process the tagged information on received frames and add tagged information to transmitted frames.

Tagged and Untagged Ports

You need to specify which ports are members of the VLAN. In the case of a tagged VLAN, it is usually a combination of both untagged ports and tagged ports. You specify which ports are tagged and which untagged when you create the VLAN.
An untagged port, whether a member of a port-based VLAN or a tagged VLAN, can be in only one VLAN at a time. However, a tagged port can be a member of more than one VLAN. A port can also be an untagged member of one VLAN and a tagged member of different VLANs simultaneously.

Displaying VLANs

To display the VLAN assignments for all of the switch ports, do the following:
1. Select the Switching tab.
The Switching tab is displayed. See Figure 19.
2. From the Switching tab, select Virtual LANs.
The VLANs page is displayed. For an example of the VLANs page, see Figure 45.

Figure 45. VLANs Page
The following fields are displayed:
■ Vlan ID— Specifies a VLAN identifier. The range is 2 to 4094. The VID of 1 is reserved for the default VLAN. The VID cannot be the same as the VID of an existing VLAN on the switch. If this VLAN is unique in your network, its VID must also be unique. However, if this VLAN is part of a larger VLAN that spans multiple switches, the VID value for the VLAN must be the same on each switch. For example, if you are creating a VLAN called Sales with a VID of 3 that spans three switches, assign the Sales VLAN on each switch the same VID value.
■ Name— Specifies a name of a VLAN. A name can be from 1 to 20 characters in length. The first character must be a letter; it cannot be a number. VLANs are easier to identify if their names reflect the functions of their subnetworks or workgroups (for example, Sales or Accounting). A name cannot contain spaces or special characters, such as asterisks (*) or exclamation points (!). A name cannot be the same as a name of an existing VLAN on the switch. If a VLAN is unique in your network, then its name must be unique as well. A VLAN that spans multiple switches must have the same name on each switch.
■ Untagged Member Ports— Indicates which ports are untagged ports.
■ Tagged Member Ports— Indicates which ports are tagged ports.

By default, there is one VLAN configured. This is the default VLAN with a Vlan ID of 1. All ports on the switch are assigned to the default VLAN. All ports in Vlan ID 1 are untagged by default.


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