Cabletron Systems SmartSwitch Router, Руководство пользователя

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Chapter 10: BGP Configuration Guide
154 SmartSwitch Router User Reference Manual
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-list option 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.