H3C Technologies H3C S7500E Series Switches - Manual (Page 247)

6-22
After you enable the BGP AS number substitution function, the PE re-advertises all routing information
to the connected CEs in the peer group, performing BGP AS number substitution based on the above
principle.
Figure 6-18 Application of BGP AS number substitution
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
In Figure 6-18 , 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 6-18 , which connects CE 2 and CE 3.
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.
MPLS L3VPN Configuration Task List
Complete the following tasks to conf
Task Remarks
Configuring VPN Instances Required
Configuring Basic MPLS L3VPN Required
Configuring Inter-Provider VPN
Optional
Configure it as needed