User Guide

BGP 1379
• If the individual routes have communities and the aggregate does not have
the ATOMIC_AGGREGATE attribute set, the aggregate is advertised
with the union of the communities from the individual routes. If the
aggregate carries the ATOMIC_AGGREGATE attribute, the aggregate is
advertised with no communities.
Dell EMC Networking BGP never aggregates paths with unknown attributes.
By default, Dell EMC Networking BGP does not aggregate paths with
different MEDs, but there is a configuration option to allow this.
Routing Policy
Route maps are used to implement redistribution policy, i.e., they are used to
filter routes and change route attributes. Route maps may be applied in the
inbound direction (before the P2 decision process) or in the outbound
direction (after best route selection but before redistribution to peer routers).
In either direction, the list of configured route maps is processed in order of
increasing sequence number.
Match clauses in a route map are processed as a logical AND, i.e., all match
clauses in a route-map must match for the route to be processed. If a route
matches all relevant match clauses in a route map, the route is permitted or
denied and route-map list processing ceases for that route. (Some match
clauses are irrelevant to routing policy, e.g., match length). ACLs are not
supported for matching prefixes when filtering routes. Use the ip prefix-list
command instead. Matching on AS numbers, community, or extended
communities is also supported.
In processing the list of route maps, each route map is processed individually.
When a match occurs, if the route is permitted, the set clauses are processed
and list processing ceases. If the route is denied, no set clauses are processed
and list processing ceases. If no match occurs, list processing continues with
the next highest numbered route map.
Unlike PBR, routing policy route maps implement an implicit deny at the end
of the last route map that filters out all routes. Routes that do not match any
match clause reach the end of the route map list and are removed.
An empty route map has a defined action. An deny route map with no match
clause matches all routes and does not perform any set actions since the
action is deny. Processing of the route-map list ceases. An empty permit route
map permits all routes, performs any set clauses, and stops processing of the
route-map list since it matched a route.