Huawei Quidway S5600 Series Operation Manual page 352

Operation Manual – Routing Protocol
Quidway S5600 Series Ethernet Switches-Release 1510
AS_Path attribute can also be used to choose and filter routes. BGP chooses the
routes containing less AS numbers with shorter path under the same circumstances.
For example, in Figure 5-5, the BGP router in AS50 will choose the path passing
through AS40 as the route to the router in AS10.
In some applications, you can increase the number of AS numbers a BGP route
contains through routing policy to control BGP routing in a flexible way.
By configuring AS path filtering list, you can have BGP routes filtered by the AS
numbers contained in the AS-Path attribute.
3) Next_Hop
Different from that of the IGP, the Next_Hop attribute of a BGP route does not
necessarily holds the IP address of the neighbor router.
The Next_Hop attribute is set in the following ways.
When a BGP speaker advertises a route generated by itself to all its neighbors, it
sets the Next_Hop attribute of the routing information to the address of its own
interface connecting to the peer.
When a BGP speaker sends a received route to one of its EBGP peer, it sets the
Next_Hop attribute of the routing information to the address of its interface
connecting to the EBGP peer.
When a BGP speaker sends a route received from one of its EBGP peer to one of
its IBGP neighbor, it does not change the Next_Hop attribute of the routing
information. But with load balancing enabled, the Next_Hop attribute is changed
when the BGP route is sent to a IBGP neighbor.
AS200
1.1.2.1/24
D=8.0.0.0
Next_Hop=1.1.2.1
Figure 5-6 The Next_Hop attribute
4) MED (Multi_Exit_Disc)
The MED attribute is only valid between two neighboring ASs. The AS receiving this
attribute will not advertise this attribute to a third AS.
D=8.0.0.0
Next_Hop=1.1.1.1
1.1.1.1/24
EBGP
EBGP
IBGP
D=8.0.0.0
Next_Hop=1.1.2.1
AS300
Huawei Technologies Proprietary
5-7
Chapter 5 BGP Configuration
AS100
8.0.0.0