In the multiaccess topology shown in Figure 1, there are three routers interconnected over a common Ethernet multiaccess network, 192.168.1.0/28. Each router is configured with the indicated IP address on the Gigabit Ethernet 0/0 interface.
Because the routers are connected over a common multiaccess broadcast network, OSPF has automatically elected a DR and BDR. In this example, R3 has been elected as the DR because its router ID is 3.3.3.3, which is the highest in this network. R2 is the BDR because it has the second highest router ID in the network.
To verify the roles of the router, use the show ip ospf interface command (Figure 2). The output generated by R1 confirms that:
- R1 is not the DR or BDR, but is a DROTHER with a default priority of 1. (1)
- The DR is R3 with router ID 3.3.3.3 at IP address 192.168.1.3, while the BDR is R2 with router ID 2.2.2.2 at IP address 192.168.1.2. (2)
- R1 has two adjacencies: one with the BDR and one with the DR. (3)
The output generated by R2 in Figure 3 confirms that:
- R2 is the BDR with a default priority of 1. (1)
- The DR is R3 with router ID 3.3.3.3 at IP address 192.168.1.3, while the BDR is R2 with router ID 2.2.2.2 at IP address 192.168.1.2. (2)
- R2 has two adjacencies; one with a neighbor with router ID 1.1.1.1 (R1) and the other with the DR. (3)
The output generated by R3 in Figure 4 confirms that:
- R3 is the DR with a default priority of 1. (1)
- The DR is R3 with router ID 3.3.3.3 at IP address 192.168.1.3, while the BDR is R2 with router ID 2.2.2.2 at IP address 192.168.1.2. (2)
- R3 has two adjacencies: one with a neighbor with router ID 1.1.1.1 (R1) and the other with the BDR. (3)