Enterasys Networks X-PeditionTM manual Forwarding VLAN, PPPoE over Vlan, 802.1Q Vlan Tag

IP Routing Protocols

Figure 5-1 802.1Q VLAN Tag

802.1Q Tag Type

Priority CFI

VLAN Identifier

The reserved Tag Type denotes the associated Ethernet frame type of the VLAN Tag while the remaining 16 tag bits comprise this control data:

•a 3-bit value indicating the user priority of the Ethernet frame for QoS purposes

•a 1-bit Canonical Format Indicator (CFI) denoting the presence of a Routing Information Field

•a 12-bit VLAN Identifier (VLAN ID) used for network assignment

The XSR lets you configure up to 4094 VLANs using the vlan command, with IDs 0 and 4095 reserved. VLAN ID 0 is used to represent the default VLAN. VLANs provide for eight priority levels but the XSR does not act on priority bits. Any VLAN packets originating from the XSR are assigned a priority of 0.

Figure 5-2depicts a typical VLAN routing setup. The LAN that a device belongs to depends on the settings of the interfaces on the VLAN switch rather than the actual systems layout.

Figure 5-2 Typical Configuration of VLAN Routing

Physical layout

WAN

XSR

VLAN Switches
Logical layout	VLAN 100 VLAN 200 VLAN 300

Forwarding VLAN, PPPoE over VLAN

It is possible for a single physical Ethernet interface to support a mixture of Ethernet, PPPoE, Ethernet VLAN, and PPPoE over VLAN traffic, as illustrated in Figure 5-3. Note that GigabitEthernet sub-interfaces 3.1 - 3.4 are all sub-interfaces associated with different VLAN IDs.

XSR User’s Guide 5-19