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 functions of the access layer are incorporated into the aggregation layer. In the design, considering that the core layer needs to have a fast convergence function, the aggregation layer performs route aggregation to reduce the number of routes. Which of the following routing protocols should L should use as the aggregation layer routing protocol?

The topology of a certain network is complex, and there are multiple paths between the core and the branch. In order to control the routing between the core and the branch, effectively use the bandwidth resources, and reduce the maintenance cost, which of the following measures is optimal?

Among the following routing protocols, the one belonging to the IGP is ______, and the one using the path vector algorithm is ______.

In the broadcast network of OSPF, there are 4 routers RTA, RTB, RTC and RTD in the same network segment, their priorities are 2, 1, 1 and 0 respectively, and the Router IDs are 192.168.1.1, 192.168.2.1, 192.168 respectively. 3.1 and 192.168.4.1. If the OSPF protocol is enabled on these 4 routers at the same time, the BDR selected by OSPF is _____.

As shown in the figure, the MSR router in the headquarters is connected to the branch through the Ethernet interface E1/0, and the connection is backed up through the ISDN network. Which of the following options is the most reasonable and feasible at this time?