Enterasys Networks X-PeditionTM manual Vlan Processing Over the XSR’s Ethernet Interfaces

IP Routing Protocols

Figure 5-3 Topology of Ethernet/PPPoE/VLAN/PPPoE over VLAN

G3.1

IP

PPPoE

G3.2

IP

VLAN 100

G3.3

IP

PPPoE

VLAN 200

G3.4

IP

PPPoE

VLAN 300

Ethernet

VLAN Processing Over the XSR’s Ethernet Interfaces

The VLAN routing process, shown in Figure 5-4, works as follows on the XSR. The following steps are reflected in the graphic below.

Figure 5-4 XSR’s VLAN Processing

					IP Routing Table
					1.2.3.0/24 F1.1
					2.2.3.0/24 F2.1
			VLAN 1200		3.3.2.0/24 F2.2
					9.9.9.0/24 F2.1 (Static)
			IP 1.2.3.4/24			F2.1
Ethernet		VLAN Tag		IP: 9.9.9.1	F1.1	F2.2
	1
					VLAN 1400
					IP 3.3.2.4/24
Priority	CFI		VLAN: 1300

Incoming VLAN tagged frame

VLAN 1300

IP 2.2.3.4/24

Ethernet VLAN Tag IP: 9.9.9.1

3

Priority CFI VLAN: 1300

Outgoing VLAN tagged frame

1.When a VLAN-tagged Ethernet frame is received, it is stripped and the tag’s VLAN ID used to map the frame to a sub-interface of the Ethernet port. Priority bits are kept internally with the frame. If a PPPoE session header exists behind the tag, the frame is further de-muxed. The matched sub-interface is marked as the incoming port. If no match is found for the VLAN ID, the frame is dropped.

2.The Ethernet frame’s IP packet is routed based on the XSR’s forwarding table which chooses the next hop and outgoing interface.

3.If the outgoing interface is associated with a VLAN by a VLAN ID, a VLAN tag including the VLAN ID is created and inserted into the outgoing Ethernet frame. If priority bits are stored with the frame, they are marked in the VLAN tag.

VLAN Processing: VLAN-enabled Ethernet to Standard LAN Interfaces

In this scenario, illustrated in Figure 5-5, the XSR does not insert a VLAN tag since there is no VLAN associated with the outgoing interface.

5-20 Configuring IP