JN0-649 Enterprise Routing and Switching Professional (JNCIP-ENT) Question and Answers

OSPF inter-area route summarization reduces the routing information exchanged between areas and the size of routing tables, and improves routing performance. OSPF inter-area route summarization enables an ABR to summarize contiguous networks into a single network and advertise the network to other areas.

Area-1 has no external connections. However, Area-1 has static route (172.16.31.0/24) that are not internal OSPF route. You can limit the external route advertisements to the area and advertise the static routes by designating the area an NSSA. In an NSSA, the ASBR (vMX1) generates NSSA external (Type 7) LSAs and floods them into the NSSA, where they are contained.

Type-7 LSAs allow an NSSA to support the presence of ASBR and their corresponding external routing information. The ABR (vMX2) converts Type-7 LSAs into Type-5 External LSAs and leaks them to the other areas, but external routes from other areas are not advertised within the NSSA.

An admin should check this and change it

https://www.packetswitch.co.uk/configuring-junos-ospf-stub-and-nssa-areas/

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/ref/statement/nssa-edit-protocols-ospf.html

https://www.juniper.net/documentation/us/en/software/junos/evpn-vxlan/topics/concept/evpn-route-type5-understanding.html#:~:text=In%20the%20control%20plane%2C%20EVPN,subnet%20connectivity%20across%20data%20centers .