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After a number of best paths is determined, this selection criteria is applied to group’s best to determine the ultimate best path.
In non-deterministic mode (the bgp non-deterministic-med command is applied), paths are compared in the order in
which they arrive. This method can lead to Dell EMC Networking OS choosing different best paths from a set of paths,
depending on the order in which they were received from the neighbors because MED may or may not get compared between
the adjacent paths. In deterministic mode, Dell EMC Networking OS compares MED between the adjacent paths within an AS
group because all paths in the AS group are from the same AS.
Weight
The weight attribute is local to the router and is not advertised to neighboring routers.
If the router learns about more than one route to the same destination, the route with the highest weight is preferred. The route
with the highest weight is installed in the IP routing table.
Local Preference
Local preference (LOCAL_PREF) represents the degree of preference within the entire AS. The higher the number, the greater
the preference for the route.
Local preference (LOCAL_PREF) is one of the criteria used to determine the best path, so keep in mind that other criteria may
impact selection, as shown in the illustration in Best Path Selection Criteria. For this example, assume that thelocal preference
(LOCAL_PREF) is the only attribute applied. In the following illustration, AS100 has two possible paths to AS 200. Although
the path through Router A is shorter (one hop instead of two), the LOCAL_PREF settings have the preferred path go through
Router B and AS300. This is advertised to all routers within AS100, causing all BGP speakers to prefer the path through Router
B.
Figure 21. BGP Local Preference
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Border Gateway Protocol IPv4 (BGPv4)