To Next Page

To Previous Page

232

• Layer 2 labels—Inner labels, used for forwarding packets from the remote PEs to the CEs. An inner

label indicates to which site, or more precisely, to which CE the packet should be sent. A PE finds

the interface for forwarding a packet according to the inner label.

If two CEs belong to the same VPN and are connected to the same PE, each CE only needs to know how

to reach the other CE.

Figure 15 VPN packet forwarding

A VPN packet is forwarded in the following way:

1. Site 1 sends an IP packet with the destination address of 1.1.1.2. CE 1 transmits the packet to PE

2. PE 1 searches VPN instance entries based on the inbound interface and destination address of the

packet. Once finding a matching entry, PE 1 labels the packet with both inner and outer labels and

forwards the packet out.

3. The MPLS backbone transmits the packet to PE 2 by outer label. The outer label is removed from

the packet at the penultimate hop.

4. PE 2 searches VPN instance entries according to the inner label and destination address of the

packet to determine the outbound interface and then forwards the packet out the interface to CE 2.

5. CE 2 transmits the packet to the destination by IP forwarding.

MPLS L3VPN networking schemes

In MPLS L3VPNs, route target attributes are used to control the advertisement and reception of VPN

routes between sites. They function independently and can be configured with multiple values to support

flexible VPN access control and implement multiple types of VPN networking schemes.

Basic VPN networking scheme

In the simplest case, all users in a VPN form a closed user group. They can forward traffic to each other,

but cannot communicate with any user outside the VPN.

For this basic VPN networking scheme, you must assign a route target to each VPN for identifying the

export target attribute and import target attribute of the VPN. Moreover, this route target cannot be used

by any other VPNs.

CE 1Site 1

PE 1

PE 2

CE 2

Site 2

2.1.1.1/24

1.1.1.2/24

1.1.1.2

Layer2

Layer1

1.1.1.2

Layer2

1.1.1.2

HP 10500 series User Manual

Other manuals for HP 10500 series