The Router ID: in an OSPF domain, used to identify each Router ID,

Electoral rules:

1. Manually specify (suggest)

2. If there is no specified by hand, use the IP address of the largest in the Loopback interface as the Router ID

3. If there is no configuration Loopback interface, then use the largest of physical interface IP address as the Router ID



Link-state information

Link information include:

1. The type of link

2. The interface IP address and mask

3, the link is connected on the neighbor routers

4. The bandwidth of the link (overhead)



Hello message:

Role: found to establish and maintain their neighbour

Routers in the OSPF link-state information exchange, you first need to establish a neighbor relations, this relationship is implemented through the Hello message, neighbor relationship, after the Hello message periodically sent to realize the function of the neighbors to keep, if in a certain period of time did not receive the Hello message, will interrupt their neighbour,

The process of OSPF neighbor build

Status:

Down: no enabled OSPF state; Neighbors expires into that state

Init: initial state, the first received the hello packets from the side (include to end the route - id), set for the state to Init

2 - way: neighbor state, cycle between send hello state (the two sides establish a session)

Initialization Exstart: the exchange of information state

Send DBD (including local information of LSA) message, election master-slave router (using the HELLO message in the ID and priority to the election, don't allow preemption, DR, DBDR to)

The state of the Exchange, Exchange information

The state, send each other DBD, inform to end all LSA local directory; At the same time, can send LSR, LSU, LSACK to learn of the LSA

Loading: Loading state (without studying the)

Send the LSR, LSU, LSACK, specialized study detailed information of the lsas

Full: adjacency state (state) studying the

LSDB synchronization with each other, that is, all the same LSA



Become a neighbor's six criteria:

1. Different rids

2. The specific area of the same flag field

3.. Subnet mask is the same as

4. Verify the same

5. The same area,

6. Hello/dead same