3Com 5500 SI - Switch - Stackable, Руководство по настройке

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8
VLAN-VPN C
ONFIGURATION
This chapter contains configuration information to create VLAN-VPNs.
VLAN-VPN Overview
The VLAN-VPN function enables packets to be transmitted across the operators'
backbone networks with VLAN tags of private networks nested in those of public
networks. In public networks, packets of this type are transmitted by their outer VLAN
tags (that is, the VLAN tags of public networks). And those of private networks, which
are nested in the VLAN tags of public networks, remain intact.
Figure 28 describes the structure of the packets with single VLAN tags.
Figure 28 Structure of packets with private network VLAN tags only
Figure 29 describes the structure of the packets with nested VLAN tags.
Figure 29 Structure of packets with nested VLAN tags
Compared with MPLS-based L2VPN, VLAN-VPN has the following features:
■
It allows Layer 2 VPN tunnels that are simpler.
■
VLAN-VPN can be implemented without the support of signalling protocols. You
can enable VLAN-VPN by static configuring.
The VLAN-VPN function provides you with the following benefits:
■
Saves public network VLAN ID resource.
■
You can have VLAN IDs of your own, which is independent of public network
VLAN IDs.
■
Provides simple Layer 2 VPN solutions for small-sized MANs or intranets.
Implementation of
VLAN-VPN
VLAN-VPN can be implemented by enabling the VLAN-VPN function on ports.
With the VLAN-VPN function enabled, a received packet is tagged with the default
VLAN tag of the receiving port no matter whether or not the packet already carries a
VLAN tag. If the packet already carries a VLAN tag, the inserted VLAN tag becomes a
nested VLAN tag in the packet. Otherwise, the packet is then transmitted with the
default VLAN tag of the port carried.