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| 6.2 |  | OSPF Operation |
| 6.2.2 |  | Step 1: Establish router adjacencies |

The first step a router takes in the OSPF operation is to establish router adjacencies. Each of the three routers shown in the figure attempts to become adjacent to another router on the same IP network.

To become adjacent with another router, RTB sends Hello packets, advertising its own router ID. Because no loopback interfaces are present, RTB chooses its highest IP address, 10.6.0.1, as its router ID.

Assuming that RTB is appropriately configured, RTB multicasts Hello packets out both S0 and E0. RTA and RTC should both receive the Hello packets. These two routers then add RTB to the Neighbor ID field of their respective Hello packets and enter the Init state with RTB.

RTB receives Hello packets from both of its neighbors and sees its own ID number, 10.6.0.1, in the Neighbor ID field. RTB declares a two-way state between itself and RTA, and a two-way state between itself and RTC.

At this point, RTB determines which routers to establish adjacencies with, based on the type of network that a particular interface resides on. If the network type is point-to-point, the router becomes adjacent with its sole link partner. If the network type is multiaccess, RTB enters the election process to become a DR or BDR. This happens unless both roles are already established, as advertised in the Hello packet header.

If an election is necessary, OSPF routers will proceed as described in the next section under Step 2: Elect a DR and a BDR. However, if an election is not necessary, the routers will enter the ExStart state, as described in the section, Step 3: Discover Routes.