L is a network design engineer. In a certain network project, in order to reduce the complexity, the small L design network adopts a two-layer architecture, and the access layer functions are incorporated into the convergence layer. In the design, the small L takes into account that the core layer needs to have a fast convergence function, and the convergence layer performs route aggregation to reduce the number of routes. Among the following routing protocols, which one should be used as the core layer routing protocol?

As shown in the figure, RTA and RTB establish an IS-IS adjacency relationship on a P2P type link. After RTB sends LSP_N to RTA, it sends LSP_N to RTA after a period of time. RTA then sends ______ to RTB. From the above, it can be seen that ______ is lost.

In the OSPF broadcast network, there are 4 routers RTA, RTB, RTC, and RTD in the same network segment. The priorities are 2, 1, 1, and 0, and the router IDs are 192.168.1.1, 192.168.2.1, 192.168.3.1 and 192.168.4.1. If OSPF is enabled on the 4 routers at the same time, the BDR selected by OSPF is _____.

In the topology shown in the figure, RTC, RTD and RTE are configured as follows:
RTC]ospf 1 router-id 2.2.2.2
RTC-ospf-1]area 2
RTC-ospf-1-area-0.0.0.2]nssa
RTC-ospf-1-area-0.0.0.2]network 30.0.0.0 0.0.0.255
RTD]ospf 1 router-id 1.1.1.1
RTD-ospf-1]area 2
RTD-ospf-1-area-0.0.0.2]network 40.0.0.0 0.0.0.255
RTE-LoopBack0] ip address 5.5.5.5 255.255.255.255
RTE]ospf 1
RTE-ospf-1]area 2
RTE-ospf-1-area-0.0.0.2]network 30.0.0.0 0.0.0.255
RTE-ospf-1-area-0.0.0.2]network 40.0.0.0 0.0.0.255
RTE-ospf-1-area-0.0.0.2]nssa
RTE-ospf-1]import-route direct
then_________.

In a certain network project, the client considers that network users may increase substantially in the future, so the network is required to have better scalability.
Which of the following measures can improve the scalability of the network?