Cabletron Systems SmartSwitch manual LocalPref Attribute Example

Chapter 10: BGP Configuration Guide

Notes on Using Communities

When originating BGP communities, the set of communities that is actually sent is the union of the communities received with the route (if any), those specified in group policy (if any), and those specified in export policy (if any).

When receiving BGP communities, the update is only matched if all communities specified in the optional-attributes-listoption of the ip-router policy create command are present in the BGP update. (If additional communities are also present in the update, it will still be matched.)

Local_Pref Attribute Example

Figure 13 shows a BGP configuration that uses the BGP local preference (Local_Pref) attribute in a sample BGP configuration with two autonomous systems.

The local preference is not set directly in the CLI, but rather is a function of the GateD preference and setpref metric. The setpref option allows GateD to set the local preference to reflect GateD's own internal preference for the route, as given by the global protocol preference value. The setpref option may be used with routing or internal type groups. BGP routes with a larger Local_Pref are preferred.

The formula used to compute the local preference is as follows:

Local_Pref = 254 – (global protocol preference for this route) + set preference metric

Note: A value greater than 254 will be reset to 254. GateD will only send Local_Pref values between 0 and 254.

In a mixed GateD and non-GateD network, the non-GateD IBGP implementation may send Local_Pref values that are greater than 254. When operating a mixed network of this type, you should make sure that all routers are restricted to sending Local_Pref values in the range metric to 254.

154 SmartSwitch Router User Reference Manual