Hello Kamal
When we talk about point to point connections in OSPF we can be talking about several different, but related things.
The first has to do with the physical type of connection being used, as is the case in this lesson. When you use a serial connection, the physical type of connection is point to point. In such a connection, there can only be two hosts, one on either end of the physical link. When such a connection is made and OSPF neighbors are created across this link, there is no DR/BDR election. This is what is being described in the lesson.
Contrary to this, if the connection between the two devices was Ethernet, then the connection is not considered a point to point connection, even though there are only two routers involved. This is because the technology being used to connect them (Ethernet) is by definition a multi access technology, allowing for multiple devices to be connected on that same network segment (such as if you had a single L2 switch and three or more routers connected to it on the same subnet). So if Ethernet was used, a DR/BDR election would still take place, even if only two routers are present on the link.
Now the OSFP network type is different from (but related to) the point to point and multi access designations of specific technologies mentioned above. This has to do with configuring OSPF to function in a particular way to accommodate the type of network being used. These network types include non-broadcast, broadcast, point to multipoint, point to multipoint non broadcast, and point to point. All of these are covered in Unit 3 of the OSPF series of lessons.
Specifically, the ip ospf network point-to-point command causes OSPF to function such that the following features are enabled or disabled:
- Automatic neighbor discovery is enabled so there is no need to configure OSPF neighbors yourself.
- No DR/BDR election take place since OSPF sees the network as a collection of point-to-point links.
- Normally used on point-to-point sub-interfaces with an IP subnet per link.
- Can also be used with multiple PVCs using only one subnet.
The network topology being used must be appropriate for the particular command to be implemented. This is most often implemented in a non-broadcast point to point topology such as that used in Frame Relay. You can find out about this command and the related topologies it accommodates in detail at the following lesson:
I hope this has been helpful!
Laz