Chapter 7: Routing Policy Configuration Guide108 SmartSwitch Router User Reference ManualPreferencePreference is the value the SSR routing process uses to order preference of routes from oneprotocol or peer over another. Preference can be set using several different configurationcommands. Preference can be set based on one network interface over another, from oneprotocol over another, or from one remote gateway over another. Preference may not beused to control the selection of routes within an Interior Gateway Protocol (IGP) This isaccomplished automatically by the protocol based on metric.Preference may be used to select routes from the same Exterior Gateway Protocol (EGP)learned from different peers or autonomous systems. Each route has only one preferencevalue associated with it, even though the preference can be set at many places usingconfiguration commands. The last or most specific preference value set for a route is thevalue used. A preference value is an arbitrarily assigned value used to determine theorder of routes to the same destination in a single routing database. The active route ischosen by the lowest preference value.A default preference is assigned to each source from which the SSR routing processreceives routes. Preference values range from 0 to 255 with the lowest number indicatingthe most preferred route.The following table summarizes the default preference values for routes learned invarious ways. The table lists the CLI commands that set preference, and shows the typesof routes to which each CLI command applies. A default preference for each type of routeis listed, and the table notes preference precedence between protocols. The narrower thescope of the statement, the higher precedence its preference value is given, but the smallerthe set of routes it affects.Table 4. Default Preference ValuesPreference Defined by CLI Command DefaultDirect connected networks ip-router global set interface 0OSPF routes ospf 10Static routes from config ip add route 60RIP routes rip set preference 100Point-to-point interface 110Routes to interfaces that aredownip-router global set interfacedown-preference120Aggregate/generate routes aggr-gen 130OSPF AS external routes ospf set ase-defaults preference 150BGP routes bgp set preference 170
