R3303-HP HSR6800 Routers Layer 2 - LAN Switching Configuration Guide

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Figure 56 VLAN termination for inter-VLAN communication (through Layer 3 Ethernet subinterfaces)
LAN-WAN communication
Most packets sent out of LANs carry VLAN tags, but some WAN protocols such as ATM, Frame Relay,
and PPP cannot recognize VLAN-tagged packets. Therefore, before sending VLAN-tagged packets to a
WAN, the sending port must locally record VLAN information and remove VLAN tags from the packets.
VLAN termination can help implement this purpose. You can configure subinterfaces to enable
LAN-WAN communication.
As shown in Figure 57, the
VLANs of the customer network are called customer VLANs (CVLANs), and
the VLANs of the service provider network are called service provider VLANs (SVLANs). When a packet
carrying a CVLAN tag enters the service provider network, it is tagged with a SVLAN tag, and
forwarded based on the SVLAN tag. When the packet is to be forwarded to an external WAN, the
gateway (Device) must perform VLAN termination for the packet and remove the two layers of VLAN tags
from the packet before sending the packet to the WAN through synchronous/asynchronous serial port
Serial 5/1.
Figure 57 VLAN termination enables LAN-WAN communication
VLAN termination configuration task list
When you configure VLAN termination, follow these guidelines:
WAN
Add a CVLAN tag
Enable QinQ and add a
SVLAN tag
Create a Layer 3
Ethernet subinterface
to perform QinQ
termination
Packets
Layer 2 network
S5/1
L2 Switch A
L2 Switch B
Device