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DES-7200 Configuration Guide Chapter 6 BGP
Configuration
6-21
6.12 Selecting the Optimal Path for BGP
The selection of the optimal route is an important part of the BGP protocol. The
following will describe the selection process of the BGP route protocol in details:
1. Discard the unreachable Next-hop route.
2. Select the route with the maximal weight.
3. Select the route with the high LOCAL_PREF attribute value.
4. Select the route generated by the local BGP speaker.
5. The route generated by the local BGP speaker includes the one generated
by the neighbor default-originate, network, redistribute, aggregate
command.
6. Select the route with the shortest AS length.
7. Select the route with the lowest ORIGIN attribute value.
8. Select the route with the smallest MED value.
9. The priority of the EBGP path is higher than that of the route of the IBGP
path and the AS
10. confederation, and the priority of the IBGP path and the AS confederation is
identical.
11. Select the route with the smallest IGP metric to reach the next hop.
12. Select the route received comparativelly earlier from the EBGP routes.
13. Select the route which advertises that the router ID of the BGP speaker is
small.
14. Select the route with the great cluster length.
15. Select the route: the value of neighbor address for which is high.
Caution
Above is the process of select the optimum route under the default
configuration. You can change the selection process of the route by the CLI
command. For instance, you can use the bgp bestpath as-path ignore
command to make the step 5 in the process of selecting the optimum route
invalid.
6.13 Configuring BGP Route Aggregation
Since the BGP-4 supports CIDR, aggregated entries are allowed to create to
reduce the size of the BGP routing table. Certainly, only when there is valid path
within the aggregation scope can the BGP aggregated entries be added to the