Configure Aggregate Routes in Juniper
You want to aggregate some of the routes in the routing table to reduce the size of the tables and to minimize the amount of routing-information advertisements between routers.
Configure an aggregate route that covers the specific routes beneath it:
# set routing-options aggregate route 10.20.8.0/21
The routing table contains prefixes for 10.20.13.0/24 and 10.20.15.0/24, which aggregate as 10.20.8.0/21. Unlike static routes, you do not specify a next hop in the set aggregate route command, because aggregate routes are not “real” routes but rather are just route summaries. The default next hop is reject. Aggregate routes become active if a more specific route beneath them becomes active. For example, if 10.20.13.0/24 becomes active, the aggregate 10.20.8.0/21 also becomes active, and you then see it in the routing table:
# run show route
inet.0: 11 destinations, 11 routes (11 active, 0 holddown, 0 hidden)
+ = Active Route, – = Last Active, * = Both
10.20.8.0/21 *[Aggregate/130] 00:00:03
Reject
10.20.13.0/24 *[Direct/0] 00:01:30
> via fe-1/0/1.0
10.20.13.1/32 *[Local/0] 00:01:30
Local via fe-1/0/1.0
10.20.15.0/24 *[Direct/0] 00:01:30
> via fe-1/0/0.0
10.20.15.1/32 *[Local/0] 00:01:30
Local via fe-1/0/0.0