Foundry Networks Switch and Router Installation And Configuration Manual page 926

Foundry Switch and Router Installation and Configuration Guide
Figure 25.3 shows an example of the default Layer 2 port-based VLAN.
DEFAULT-VLAN
VLAN ID = 1
Layer 2 Port-based VLAN
By default, all ports belong to a single
port-based VLAN, DEFAULT-VLAN.
Thus, all ports belong to a single
Layer 2 broadcast domain.
Figure 25.3 Default Layer 2 port-based VLAN
When you configure a port-based VLAN, one of the configuration items you provide is the ports that are in the
VLAN. When you configure the VLAN, the Foundry device automatically removes the ports that you place in the
VLAN from DEFAULT-VLAN. By removing the ports from the default VLAN, the Foundry device ensures that each
port resides in only one Layer 2 broadcast domain.
NOTE: Information for the default VLAN is available only after you define another VLAN.
Some network configurations may require that a port be able to reside in two or more Layer 2 broadcast domains
(port-based VLANs). In this case, you can enable a port to reside in multiple port-based VLANs by tagging the
port. See the following section.
If your network requires that you use VLAN ID 1 for a user-configured VLAN, you can reassign the default VLAN to
another valid VLAN ID. See "Assigning a Different VLAN ID to the Default VLAN" on page 25-16.
802.1q Tagging
802.1q tagging is an IEEE standard that allows a networking device to add information to a Layer 2 packet in order
to identify the VLAN membership of the packet. Foundry devices tag a packet by adding a four-byte tag to the
packet. The tag contains the tag value, which identifies the data as a tag, and also contains the VLAN ID of the
VLAN from which the packet is sent.
• The default tag value is 8100 (hexadecimal). This value comes from the 802.1q specification. You can
change this tag value on a global basis on Foundry devices if needed to be compatible with other vendors'
equipment.
25 - 6 December 2000