Information Technology Reference
In-Depth Information
Figure 10-33 shows the label-forwarding path from PE2 to PE1. Because of PHP, the top
label is popped at RR1 and RR2.
Figure 10-33
Label-Forwarding Path
17
24
IP Packet
24
24
IP Packet
RR2
RR1
19
24
IP Packet
18
24
24
IP Packet
24
IP Packet
ASBR
1
ASBR
2
AS 200
AS 100
PE2
PE1
IP Packet
IP Packet
AS 65000
AS 65000
VPNa
Site 2
VPNa
Site 1
CE2
CE1
Summary
When BGP is extended with multiprotocol capabilities, VPNv4 prefixes can be carried
within BGP. BGP multiprotocol extension makes it possible to support VPNv4 prefixes,
extended communities, and BGP labels for IPv4 prefixes.
MPLS is a service-enabling technology that allows connection-oriented packet forwarding
along a preestablished label path. MPLS VPN is a VPN service that is provisioned over an
MPLS network.
Depending on the requirements, various VPN connection models are available. A basic
Layer 3 VPN uses iBGP to exchange VPN information, yet an inter-AS VPN may involve
a combination of iBGP and eBGP. The carrier's carrier VPN model allows a VPN provider
to carry full Internet routes and provide hierarchical VPN services.
