When OSPF adjacency is formed, the router has several state changes. These states have been defined in OSPF RFC 2328 Part 10.1, and the following is a detailed explanation of each state.
Components used
This article is not limited to specific software and hardware versions.
The information provided in this article is created from the device in a specific laboratory environment. All devices in this article have begun to be configured for the default (default). If working on a real network, make sure to use it before knowing the potential impact of all commands.
Come down
This is the first OSPF neighbor state. It means that the information (hello) is not obtained from this neighbor, but the hello packet may still be sent to the neighbor in this state.
During a fully approached neighbor state, if the router does not receive hello packets from neighbors within RouterDeadInterval time (RouterDeadInterval = 4*HelloInterval by default), the neighbor state then changes from full to down.
attempt
This state is adjacent only valid in the NBMA environment. An attempt means that the router sends hello packets to the neighbors, but does not get any information.
Init
This status specifies that the router receives a hello packet from its neighbor, but the hello packet that accepts the router ID is not included. When the router receives a hello packet from adjacent, a valid packet in which it should list the sender's router ID as a reply is received.
Two-way
This state selects two-way communication established between the two routers. Two-way means that each router sees other hello packets. When the router that received the hello packet is within the received hello packet adjacency domain, it is obtained by looking at its own router ID. In this state, whether the router decides to become adjacent to this neighbor. In broadcasting quality, the router only becomes with the specified router (DR) and the backup specified router (BDR); it insists on other adjacent neighbors in the bidirectional state.
At the end of this phase, DR and BDR selections. For more information about the DR selection process, see DR selection.
Exstart
Once DR and BDR are selected, the information about the actual transaction process connection status can begin between the router and their DR and BDR.
In this state, the router establishes a master-slave relationship with their DR and BDR and selects the initial sequence number to form the adjacency relationship. The router becomes the master with a higher router ID and starts switching, and is likewise the only router that can increase the sequence number. Note that a process that will logically consider during the master-slave relationship, DR/BDR with the highest router ID will become the master. Remember that DR/BDR selection may be due to the high priority in the router configuration purely rather than the highest router ID. Therefore, it is very likely that DR plays a subordinate role.
Exchange
In the exchange state, the OSPF router exchanges database descriptor (DBD) packets. The database descriptor contains a link state broadcast (LSA) header and describes the contents of the entire link state database. Each DBD packet has a sequence number that is explicitly recognized. The router also sends a link state request packet containing the entire LSA) and a link state update packet (in this state. The content of the received DBD is compared with the information contained in the router link state database to check whether the information of the new or more current connection state is available and adjacent.
load
In this state, the actual exchange of information in the connection state occurs. Based on the information provided by DBDs, the router sends a link status request packet. The adjacent update packet in the link state and then provides information on the requested connection state. During adjacency, if the router accepts an outdated or missing LSA, it requests the LSA by sending a link status request packet.
full
In this state, the routers are sufficiently adjacent to each other. All routers and network LSAs are exchanged and the router's database is fully synchronized.
Fully normal state is OSPF router. If the router is stuck in another state, it is implied that there is a problem to form an adjacency. The only exception to this is a two-way state, which is normal on the broadcast network. Routers reach full state with only their DR and BDR. Neighbors always see each other in two directions. Article entry: csh Editor in charge: csh
Components used
This article is not limited to specific software and hardware versions.
The information provided in this article is created from the device in a specific laboratory environment. All devices in this article have begun to be configured for the default (default). If working on a real network, make sure to use it before knowing the potential impact of all commands.
Come down
This is the first OSPF neighbor state. It means that the information (hello) is not obtained from this neighbor, but the hello packet may still be sent to the neighbor in this state.
During a fully approached neighbor state, if the router does not receive hello packets from neighbors within RouterDeadInterval time (RouterDeadInterval = 4*HelloInterval by default), the neighbor state then changes from full to down.
attempt
This state is adjacent only valid in the NBMA environment. An attempt means that the router sends hello packets to the neighbors, but does not get any information.
Init
This status specifies that the router receives a hello packet from its neighbor, but the hello packet that accepts the router ID is not included. When the router receives a hello packet from adjacent, a valid packet in which it should list the sender's router ID as a reply is received.
Two-way
This state selects two-way communication established between the two routers. Two-way means that each router sees other hello packets. When the router that received the hello packet is within the received hello packet adjacency domain, it is obtained by looking at its own router ID. In this state, whether the router decides to become adjacent to this neighbor. In broadcasting quality, the router only becomes with the specified router (DR) and the backup specified router (BDR); it insists on other adjacent neighbors in the bidirectional state.
At the end of this phase, DR and BDR selections. For more information about the DR selection process, see DR selection.
Exstart
Once DR and BDR are selected, the information about the actual transaction process connection status can begin between the router and their DR and BDR.
In this state, the router establishes a master-slave relationship with their DR and BDR and selects the initial sequence number to form the adjacency relationship. The router becomes the master with a higher router ID and starts switching, and is likewise the only router that can increase the sequence number. Note that a process that will logically consider during the master-slave relationship, DR/BDR with the highest router ID will become the master. Remember that DR/BDR selection may be due to the high priority in the router configuration purely rather than the highest router ID. Therefore, it is very likely that DR plays a subordinate role.
Exchange
In the exchange state, the OSPF router exchanges database descriptor (DBD) packets. The database descriptor contains a link state broadcast (LSA) header and describes the contents of the entire link state database. Each DBD packet has a sequence number that is explicitly recognized. The router also sends a link state request packet containing the entire LSA) and a link state update packet (in this state. The content of the received DBD is compared with the information contained in the router link state database to check whether the information of the new or more current connection state is available and adjacent.
load
In this state, the actual exchange of information in the connection state occurs. Based on the information provided by DBDs, the router sends a link status request packet. The adjacent update packet in the link state and then provides information on the requested connection state. During adjacency, if the router accepts an outdated or missing LSA, it requests the LSA by sending a link status request packet.
full
In this state, the routers are sufficiently adjacent to each other. All routers and network LSAs are exchanged and the router's database is fully synchronized.
Fully normal state is OSPF router. If the router is stuck in another state, it is implied that there is a problem to form an adjacency. The only exception to this is a two-way state, which is normal on the broadcast network. Routers reach full state with only their DR and BDR. Neighbors always see each other in two directions. Article entry: csh Editor in charge: csh