Dell PowerConnect FCS624S Configuration Guide - Page 1059

Optional configuration tasks 30 You can enable the Layer 3 Switch to always compare the MEDs, regardless of the AS information in the paths. For example, if the router receives UPDATES for the same route from neighbors in three autonomous systems, the router would compare the MEDs of all the paths together, rather than comparing the MEDs for the paths in each AS individually. NOTE By default, value 0 (most favorable) is used in MED comparison when the MED attribute is not present. The default MED comparison results in the Layer 3 Switch favoring the route paths that are missing their MEDs. You can use the med-missing-as-worst command to make the Layer 3 Switch regard a BGP route with a missing MED attribute as the least favorable route, when comparing the MEDs of the routes. NOTE MED comparison is not performed for internal routes originated within the local AS or confederation. To configure the router to always compare MEDs, enter the following command. PowerConnect(config-bgp-router)#always-compare-med Syntax: [no] always-compare-med Treating missing MEDs as the worst MEDs By default, the Layer 3 Switch favors a lower MED over a higher MED during MED comparison. Since the Layer 3 Switch assigns the value 0 to a route path MED if the MED value is missing, the default MED comparison results in the Layer 3 Switch favoring the route paths that are missing their MEDs. To change this behavior so that the Layer 3 Switch favors a route that has a MED over a route that is missing its MED, enter the following command at the BGP4 configuration level of the CLI. PowerConnect(config-bgp-router)#med-missing-as-worst Syntax: [no] med-missing-as-worst NOTE This command affects route selection only when route paths are selected based on MED comparison. It is still possible for a route path that is missing its MED to be selected based on other criteria. For example, a route path with no MED can be selected if its weight is larger than the weights of the other route paths. Configuring route reflection parameters Normally, all the BGP routers within an AS are fully meshed. Each of the routers has an IBGP session with each of the other BGP routers in the AS. Each IBGP router thus has a route for each of its IBGP neighbors. For large autonomous systems containing many IBGP routers, the IBGP route information in each of the fully-meshed IBGP routers can introduce too much administrative overhead. To avoid this problem, you can hierarchically organize your IGP routers into clusters: PowerConnect B-Series FCX Configuration Guide 53-1002266-01 1017