Dell Force10 S4820T S4820T Configuration Guide - Page 188

www.dell.com | support.dell.com 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 the illustration in Best Path Selection Criteria. For this example, assume that LOCAL_PREF is the only attribute applied. In the illustration below, 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. 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 Multi-Exit Discriminators (MEDs) If two Autonomous Systems (AS) connect in more than one place, a Multi-Exit Discriminator (MED) can be used to assign a preference to a preferred path. The MED 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. 188 | Border Gateway Protocol IPv4 (BGPv4)