H3C Technologies H3C S12500-X Series Switches - Manual (Page 129)

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Figure 46 Application of BGP AS number substitution
In Figure 46 , both Site and Site 2 use the AS number 800. AS number substitution is enabled on PE 2 for
CE 2. Before advertising updates received from CE 1 to CE 2, PE 2 substitutes its own AS number 100
for the AS number 800. In this way, CE 2 can correctly receive the routing information from CE 1.
However, the AS number substitution function also introduces a routing loop in Site 2 because route
updates originated from CE 3 can be advertised back to Site 2 through PE 2 and CE 2. To remove the
routing loop, you can configure a routing policy on PE 2 to add the SoO attribute to route updates
received from CE 2 and CE 3 so that PE 2 does not advertise route updates from CE 3 to CE 2.
NOTE:
The device does not support adding the SoO attribute to routes.
MPLS L3VPN configuration task list
Tasks at a glance
Configuring basic MPLS L3VPN
Configuring inter-AS VPN
Configuring nested VPN
Configuring HoVPN
Configuring an OSPF sham link
Specifying the VPN label processing mode on the egress PE
Configuring BGP AS number substitution
Enabling SNMP notifications for MPLS L3VPN
Configuring basic MPLS L3VPN
Tasks at a glance
Configuring VPN instances :
1. (Required.) Creating a VPN instance
MPLS backbone
VPNv4_Update: 10.1.0.0/16
RD: 100:1
AS_PATH: 800
EBGP_Update: 10.1.0.0/16
AS_PATH: 100, 100
PE 1 PE 2
CE 3
AS 800
Site 2
EBGP_Update: 10.1.0.0/16
AS_PATH: 800
AS 800
Site 1
AS 100
CE 1
CE 2