Operation Manual – MPLS L3VPN
H3C S9500 Series Routing Switches
Chapter 1 MPLS L3VPN Configuration
1-23
MPLS backbone
VPNv4_Update:10.1.0.0/16
RD:10.1.1.1/32
AS_PATH:800
EBGP_Update:10.1.1.1/32
AS_PATH:100,100
PE 1
PE 2
CE 3
AS 800
AS 800
EBGP_Update:10.1.1.1/32
AS_PATH:800
AS 800
AS 100
CE 1
CE 2
Figure 1-17
Application of BGP AS number substitution
In
Figure 1-17
, both CE 1 and CE 2 use the AS number of 800. AS number substitution
is enabled on PE 2 for CE 2. Before advertising updates received from CE 1 to CE 2,
PE 2 finds that an AS number in the AS_PATH is the same as that of CE 2 and hence
substitutes its own AS number 100 for the AS number. In this way, CE 2 can normally
receive the routing information from CE 1.
AS number substitution also applies to a PE connecting multiple CEs through different
interfaces, such as PE 2 in
Figure 1-17
, which connects CE 2 and CE 3.
Note:
For a multi-homed CE, that is, a CE connected with multiple PEs, the BGP AS number
substitution function must be used in combination with the site-of-origin (SOO) function.
Otherwise, routing loops may appear.
1.2 MPLS L3VPN Configuration Task List
Task
Remarks
Configuring VPN Instances
Required
Configuring Basic MPLS L3VPN
Required
Configuring Inter-Provider VPN
Optional
Configure it as needed
Configuring HoVPN
Optional
Configure it as needed
Configuring OSPF Sham Link
Optional
Configure it as needed
Configuring Multi-VPN-instance CE
Optional
Configure it as needed
