Describes how aggregation policies control aggregate route generation, filter or suppress contributing routes, modify aggregate attributes, and apply deterministic processing to more-specific routes.
An aggregation policy is a route policy that
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you attach at the aggregation attach point
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controls whether the system generates an aggregate route based on the presence of more-specific routes, and
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can modify valid BGP attributes on the aggregate route while controlling how more-specific routes contribute.
Aggregation attach point behavior
The aggregation attach point generates an aggregate route for advertisement if certain subcomponents of the aggregate are present.
Policies attached at this attach point can:
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determine whether the system generates the aggregate, and
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set valid BGP attributes on the aggregated route.
The system generates an aggregate if any routes evaluated by the named policy pass the policy.
Example:
route-policy sample
if destination in (10.0.0.0/8 ge 8 le 25) then
set community (10:33)
endif
if destination in (10.2.0.0/24) then
drop
endif
if destination in (10.1.0.0/24) then
suppress-route
endif
end-policy
router bgp 2
address-family ipv4
aggregate-address 10.0.0.0/8 route-policy sample
In this example:
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The system generates the aggregate 10.0.0.0/8 if any component routes in the range 10.0.0.0/8 ge 8 le 25 pass the policy.
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The system drops routes matching 10.2.0.0/24. These routes do not contribute.
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The system suppresses routes matching 10.1.0.0/24.
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The system may set the community 10:33 on the aggregate.
Attribute modification on aggregates
Policies attached at the aggregation attach point may set valid BGP attributes on the aggregate route. Actions such as setting community values or MED affect the aggregate the system generates.
In the policy language, you can set attributes on the aggregate using normal action operations. The system generates the aggregate if at least one evaluated route passes the policy.
Suppress-route behavior
When you do not set summary-only , the system advertises both the aggregate and more-specific routes.
You can selectively filter specific component routes using the suppress-route keyword.
In the policy language:
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Select the route and set the suppress flag to control suppression.
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This approach replaces the traditional suppress map mechanism.
Cumulative effects on aggregate attributes
Each time the aggregation policy matches a more-specific route, it may modify aggregate attributes through set operations. These effects accumulate with each match.
route-policy
bumping-aggregation
set med +5
end-policyEach contributing more-specific route increments the aggregate MED by 5.
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If 3 matching more-specific routes exist, the aggregate MED becomes default plus 15 .
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If 17 matching more-specific routes exist, the aggregate MED becomes default plus 85 .
Drop behavior in aggregation
A drop in an aggregation policy does not prevent the system from generating the aggregate. It only prevents the current more-specific route from contributing to the aggregate.
The system generates the aggregate when any other more-specific route passes the policy. A single passing more-specific route is sufficient for the system to create the aggregate.
Deterministic but unspecified processing order
The system applies the aggregation policy to prefix paths in a deterministic, but unspecified, order. The system processes routes in the same order each time for a given set of routes, but the order cannot be predicted.