Foundry Networks Switch and Router Installation And Configuration Manual page 923

Figure 25.1 shows an example of a Foundry device on which a Layer 2 port-based VLAN has been configured.
DEFAULT-VLAN
VLAN ID = 1
Layer 2 Port-based VLAN
User-configured port-based VLAN
When you add a port-based VLAN,
the device removes all the ports in the
new VLAN from DEFAULT-VLAN.
Figure 25.1 Foundry device containing user-defined Layer 2 port-based VLAN
A port can belong to only one port-based VLAN, unless you apply 802.1q tagging to the port. 802.1q tagging
allows the port to add a four-byte tag field, which contains the VLAN ID, to each packet sent on the port. You also
can configure port-based VLANs that span multiple devices by tagging the ports within the VLAN. The tag
enables each device that receives the packet to determine the VLAN the packet belongs to. 802.1q tagging
applies only to Layer 2 VLANs, not to Layer 3 VLANs.
Since each port-based VLAN is a separate Layer 2 broadcast domain, by default each VLAN runs a separate
instance of the Spanning Tree Protocol (STP).
Layer 2 traffic is bridged within a port-based VLAN and Layer 2 broadcasts are sent to all the ports within the
VLAN.
Layer 3 Protocol-Based VLANs
If you want some or all of the ports within a port-based VLAN to be organized according to Layer 3 protocol, you
must configure a Layer 3 protocol-based VLAN within the port-based VLAN.
You can configure each of the following types of protocol-based VLAN within a port-based VLAN. All the ports in
the Layer 3 VLAN must be in the same Layer 2 VLAN.
• AppleTalk – The device sends AppleTalk broadcasts to all ports within the AppleTalk protocol VLAN.
• IP – The device sends IP broadcasts to all ports within the IP protocol VLAN.
December 2000
Configuring Virtual LANs (VLANs)
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