Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 200

www.dell.com | support.dell.com 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 FTOS choosing different best paths from a set of paths, depending on the order in which they were received from the neighbors since MED may or may not get compared between adjacent paths. In deterministic mode, FTOS compares MED between adjacent paths within an AS group since 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 will be 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. The 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 Figure 12-4. For this example, assume that LOCAL_PREF is the only attribute applied. In Figure 12-5, AS100 has two possible paths to AS 200. Although the path through the 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 12-5. LOCAL_PREF Example AS 100 Router A Router B Set Local Preference to 100 T1 Link Router C AS 200 Set Local Preference to 200 Router E OC3 Link Router D Router E AS 300 Router F 200 | Border Gateway Protocol IPv4 (BGPv4)