[j-nsp] BGP strange Next hop behavior (in JNCIP)

[medrees]

Hi Expertise

     I’m wondering from strange behavior for two IBGP session included in
JNCIP_StudyGuide, I have one router make aggregation for the whole network
10/8(R5 in case study of EBGP) and where the routers inside the other ISIS
are level-1 routers (R1 & R6) so they reach the Level1-2 router R5 Lo0
 through the default route.

We have two scenarios:

1-   when this route inserted in their BGP table the R1 which receive this
aggregated subnet (with Protocol NH of the router which created the
aggregated route R5) through another Level1-2 router R3 will simply choose
this subnet more preferred than the default route and the session of the BGP
between R1 & R3 will flap and it is normal behavior .
2- The abnormal behavior appear in the other Level-1 area which has direct
physical connection with the aggregated router R5 the route won’t be
inserted in the BGP active table but it will be inserted as Hidden route
which cause the Level-1 router R6 keep the IBGP session up.

The two issues solved by use static route for the next hop of this
aggregated route toward the neighbor while sent this update to be preferred
more than even the aggregated BGP route or the Default ISIS route. 

But the question is why the remote router choose this route as active one
while the direct connected router (Route-reflector client ) flagged this
route as hidden route??