27.3.2 Connecting to neighboring routers
- <Structure of this section>
(1) Hello datagram
Routers running OSPFv3 send hello packets on each interface to verify that the links between routers are active. A hello packet is the means by which a router recognizes other routers running OSPFv3.
(2) Inter-Router Connection Conditions
For each network that provides a direct connection between routers, the interface parameters below must be consistent among all connected routers. Routers that do not share the same parameters are not considered to be connected.
(a) Area ID
To establish a direct connection between routers, the interfaces on both routers must be assigned the same area ID.
(b) Hello Interval and Dead Interval
In OSPFv3, a router sends hello packets so that directly connected routers will detect it. The hello interval is the sending interval for hello packets.The dead interval is the number of seconds that a router's hello packets must not have been seen before its neighbors declare the connection down. For a router to properly judge when a connection is lost, these two parameters must have the same values on the interfaces of the directly connected routers.
(c) Area settings
The information reported to an area differs for stub areas and other area types. To allow OSPFv3 to determine that two routers are directly connected, the areas to which the interfaces belong must share the same stub configuration.
(d) Instance ID
OSPFv3 advertises an instance ID as a group ID to define groups of connected routers. The interfaces of routers that exchange routing information with each other must share the same instance ID.