Huawei Quidway S5600 Series Operation Manual page 351

Operation Manual – Routing Protocol
Quidway S5600 Series Ethernet Switches-Release 1510
EGP: BGP routes with their Origin attributes being EGP are obtained through
EGP.
Incomplete: BGP routes with their Origin attributes being Incomplete have the
least priority. This value does not indicate that the BGP route is unreachable; it
means the source of the BGP route cannot be determined. The Origin attribute of
a BGP route imported through the import-route command is Incomplete.
2) AS_Path
The AS_Path attribute holds the numbers of all the ASs that a route passes from the
source to the destination. AS numbers in this attribute are in the order the route passes
the ASs. Before a BGP speaker advertises a route to the BGP speakers of other ASs, it
adds the local AS number to the head of the AS number queue in the AS_Path attribute.
According to the AS_Path attribute of a received BGP route, a router can retrieve the
information about the ASs the route passes. In AS_Path attribute, AS numbers are
listed by the distances between the ASs and the local AS. The number of the AS that is
closest to the local AS is listed in the head, as shown in Figure 5-5.
D=8.0.0.0
(10)
Figure 5-5 AS_Path attribute
Normally, a router with BGP employed discards the routes that contain local AS number
in the AS_Path attribute. This eliminates routing loops.
Note:
In VRP implementations, you can use the peer allow-as-loop command to allow AS
number repetition to meet some special needs.
8.0.0.0
AS10
D=8.0.0.0
(10)
AS20
D=8.0.0.0
(20,10)
D=8.0.0.0
(30,20,10)
AS30
Huawei Technologies Proprietary
AS40
D=8.0.0.0
(40,10)
AS50
5-6
Chapter 5 BGP Configuration