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12. If two paths have the same router ID, prefer the path with the lowest cluster ID length. Paths without a cluster ID length are
set to a 0 cluster ID length.
13. Prefer the path originated from the neighbor with the lowest address. (The neighbor address is used in the BGP neighbor
configuration and corresponds to the remote peer used in the TCP connection with the local router.)
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 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 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
effect selection, as shown in the illustration in Best Path Selection Criteria. For this example, assume that the local preference
(LOCAL_PREF) is the only attribute applied. In the following illustration, AS100 has two possible paths to AS200. 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 20. BGP Local Preference
Border Gateway Protocol IPv4 (BGPv4)
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