Single-region OSPF and DR and BDR elections

First, I will draw the following topology, which is marked in the basic configuration map of each vro. The loopback ports are added to the three routers, respectively, with the addresses 1.1.1.1; 2.2.2.2; 3.3.3.3. In the subsequent configuration, each route uses its own loopback port address as its own router ID. (To facilitate OSPF region planning and troubleshooting, a loopback port address is usually configured as the router ID of the route. If the router ID or interface address is changed after OSPF takes effect, it takes effect only after OSPF is restarted or the router is restarted .)

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M00/4C/2B/wKiom1Q3rs6DGyf4AAD3rBb2VRU997.jpg "Title =" single 1.png "alt =" wkiom1q3rs6dgyf4aad3rbb2vru997.jpg "/>

Well, let's take a look at the basic configuration process of rt1.

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M01/4C/2B/wKiom1Q3sAvhZEhRAADZ-0sToHg855.jpg "Title =" 1.png" alt = "wKiom1Q3sAvhZEhRAADZ-0sToHg855.jpg"/>

After all the basic configurations are complete, I enable OSPF on the three routes, configure the region, and start OSPF on the specified interface (one interface can be added to only one region .)

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M00/4C/2D/wKioL1Q3scvi7yXoAAFkr-hpxcE327.jpg "Title =" 2.jpg" alt = "wKioL1Q3scvi7yXoAAFkr-hpxcE327.jpg"/>

You can see that the two interfaces 0/1 and 0/0 have reached the full status with the other interface, and both of the three routes have reached the full status. The OSPF of the three routes in a single region is ready.

Next we will analyze the election of DR and BDR.

According to the principle that the priority is the same, the priority of the router ID is high. The G0/0/1 of rt2 will be elected as the Dr of the network between rt1 and rt2. Similarly, the G0/0/0 of rT3 will be elected as the network Dr between rt2 and rT3, while the G0/0/1 of rT3 will be elected as the network Dr between rT3 and rt1.

Then let's take a look at the results:

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M01/4C/2D/wKioL1Q3s-ax9mawAADd_g3qJe8243.jpg "Title =" R1 peer.png "alt =" wKioL1Q3s-ax9mawAADd_g3qJe8243.jpg "/>

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M02/4C/2D/wKioL1Q3wgaRy3KxAAD5j6MII50250.jpg "Title =" R2 peer.png "alt =" wkiol1q3wgary3kxaad5j6mii50250.jpg "/>

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M02/4C/2C/wKiom1Q3weSgpX5fAADvW-m6UNc299.jpg "Title =" R3 peer.png "alt =" wKiom1Q3weSgpX5fAADvW-m6UNc299.jpg "/>

What we can see is not the expected result. On the contrary, the reason is that if OSPF is enabled for the three routes at the same time, the DR and BDR elections are conducted according to the above principles, however, when I start OSPF, the order is rt1, rt2, rT3, so the election of DR and BDR is not based on the priority and router ID, but on the OSPF startup order, as a result, we can talk about three routes and reset OSPF process at the same time to eliminate this interference.

Single-region OSPF and DR and BDR elections