Huawei Quidway NetEngine80E Configuration Manual page 954

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
Item
peer fake-as
peer substitute-as
During BGP route selection, BGP compares the AS_Path length by calculating the number of
ASs included in the AS_Sequence if AS_Sequence is carried in a route. If both AS_Sequence
and AS_Set are carried in the route, BGP considers the AS_Path length to be the number of ASs
included in the AS_Sequence plus 1.
Deleting Private AS Numbers
As public AS resources are limited, carriers generally use private AS numbers when deploying
VPNs. Private AS numbers, however, must not be advertised to the Internet because they may
cause routing loops. In
Figure 8-19 Networking in which a private AS needs to be deleted
AS 65001
10.0.0.0/8
Issue 02 (2014-09-30)
Description
After the command is configured, BGP can use a fake AS
number to set up a BGP peer relationship.
If the local device uses the actual AS number to establish an
EBGP peer relationship with a remote device, the actual AS
number is carried in the AS_Path of the route sent to the
remote device. If the local device uses the fake AS number
to establish the EBGP peer relationship, the fake AS number
is carried in the AS_Path of the route sent to the remote
device.
If the command is configured and an AS in the AS_Path
carried in the route sent by a PE to the CE of the specified
peer is the same as the AS of the CE, the PE replaces the AS
with the local AS.
NOTE
Figure 8-19, both ISP1 and ISP2 use 65001 as a private AS number.
On B: peer C public-as-only
Router A
Update
10.0.0.0/8
AS_Path: 65001
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The peer substitute-as command applies only to PEs in BGP
MPLS IP/VPN scenarios and may cause routing loops if it is
improperly configured. Therefore, exercise caution when using the
command.
ISP1
AS 100
Router B
Update
10.0.0.0/8
AS_Path: 100
8 BGP Configuration
ISP2
AS 200
Router C
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