Topology

graph LR
net1(LAN1_172.17.99.0/24) 
net1 <--> R1
R1 <--> |WAN1_10.10.10.8/30|R4

Configuration and Interpretations

Desired outcome: I want to configure a generated route on R1 for the prefix 172.17.99.0. Currently, the prefix 172.17.99.0/24 is directly attached to ge-0/0/6. I want to make R1 advertise the generated route 172.17.96.0/19 toward its BGP neighbor R4 only when R1 receives the BGP route 10.22.1.0/26 from R4 (which is configured as an aggregate route on R4) and successfully imports it from BGP into inet.0. On R1, at the moment there is only one contributing route for the generated route, which is 17.17.99.0/24.

Topology

graph LR
net1(LAN1_172.17.99.0/24) 
net1 <--> R1
R1 <--> |WAN1_10.10.10.8/30|R4

Configuration and Analysis

The default next hop of an aggregate route is reject:

root@R4> show configuration routing-options rib inet.0 aggregate 
defaults {
    preference 189;
}
route 10.22.1.0/26;

root@R4> 
root@R4> show route protocol aggregate 

inet.0: 15 destinations, 17 routes (15 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.22.1.0/26       *[Aggregate/189] 00:00:58
                       Reject

inet6.0: 3 destinations, 3 routes (3 active, 0 holddown, 0 hidden)

root@R4> 
root@R4> show route 10.22.1.0/26 exact detail 

inet.0: 15 destinations, 17 routes (15 active, 0 holddown, 0 hidden)
10.22.1.0/26 (1 entry, 1 announced)
        *Aggregate Preference: 189
                Next hop type: Reject, Next hop index: 0
                Address: 0x77c5434
                Next-hop reference count: 2
                Kernel Table Id: 0
                State: <Active Int Ext>
                Local AS:    22 
                Age: 7:22 
                Validation State: unverified 
                Task: Aggregate
                Announcement bits (2): 0-KRT 5-Resolve tree 3 
                AS path: I  (LocalAgg)
                Flags:                  Depth: 0        Active
                AS path list:
                AS path: I Refcount: 2
                Contributing Routes (2):
                        10.22.1.0/27 proto Direct
                        10.22.1.32/27 proto Static
                Thread: junos-main 

root@R4> 

#LessonLearned The contributing routes may be of different routing protocols or pseudoprotocols.