Bgp Configuration Task List - Edge-Core ES4626 User Manual

BGP-4 can share and query inner IP route table through relevant mechanisms, but it
has its own route table. In the BGP route table, each route has a network number, AS
listing information (also called AS path) that it passed and some routing attributes (such
as origin). The routing attribute that BGP-4 used is very complex, this attribute can be
used as metrics to select path.
4．Route-selecting policy of BGP
When receiving BGP notification about a same route from several neighbors,
selecting the best route need to be take into account after routing filtering. This process is
called BGP route selecting process. BGP route selecting process will start only when the
following conditions are fulfilled:
The switch's route must be next hop reachable. That is in the route table there is
the route that can reach the next hop.
BGP must be synchronized with IGP (unless asynchronism is configured; only
restricted to IBGP)
BGP route selecting process is based on the BGP attribute. When there are several
routes that indicate the same destination, BGP need select the best route to the
destination. The decision-making process is as the following:
1．Select the route with the most weight first;
2. If the weights are the same, select the route with the most local preference;
3. If the local preferences are the same, select the route generated by local switch.
4. If the local preferences are the same and there is no route generated by local
switch, select the route with the shortest AS path;
5. If the AS paths are the same, select the route with the lowest "origin" type
（IGP<EGP<INCOMPLETE）;
6. If the "origin" types are the same, select the route with the lowest MED attribute.
Unless activating command "bgp always-compare-med", this comparison is only available
among the routes from the same neighbor AS.
7. If the MED attributes are the same, EBGP is preferable to outer confederation and
outer confederation is preferable to IBGP.
8. If it's still the same by now, BGP router ID （router ID） is used to break the balance.
The best route is the one from the least router ID.

17.8.2 BGP Configuration Task List

The BGP configuration tasks include basic and advanced tasks. Basic BGP
configuration tasks include the following:
1．Enable BGP Routing (required)
2．Configure BGP Neighbors (required)
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