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Cisco ASDM User Guide
OL-16647-01
Chapter 43 Monitoring Routing
Monitoring OSPF Neighbors
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2-Way—This state designates that bi-directional communication has been established between
the security appliance and the neighbor. Bi-directional means that each device has seen the hello
packet from the other device. This state is attained when the router receiving the hello packet
sees its own Router ID within the neighbor field of the received hello packet. At this state, the
security appliance decides whether to become adjacent with this neighbor. On broadcast media
and non-broadcast multiaccess networks, a the security appliance becomes full only with the
designated router and the backup designated router; it stays in the 2-way state with all other
neighbors. On point-to-point and point-to-multipoint networks, the security appliance becomes
full with all connected neighbors.
At the end of this stage, the DR and BDR for broadcast and non-broadcast multiaccess networks
are elected.
Note Receiving a Database Descriptor packet from a neighbor in the Init state will also a cause a
transition to 2-way state.
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Exstart—Once the DR and BDR are elected, the actual process of exchanging link state
information begins between the security appliance and the DR and BDR.
In this state, the security appliance and the DR and BDR establish a master-slave relationship
and choose the initial sequence number for adjacency formation. The device with the higher
router ID becomes the master and starts the exchange and is therefore the only device that can
increment the sequence number.
Note DR/BDR election occurs by virtue of a higher priority configured on the device instead of
highest router ID. Therefore, it is possible that a DR plays the role of slave in this state.
Master/slave election is on a per-neighbor basis. If multiple devices have the same DR priority,
then the device with the highest IP address becomes the DR.
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Exchange—In the exchange state, OSPF neighbors exchange DBD packets. Database
descriptors contain LSA headers only and describe the contents of the entire link state database.
Each DBD packet has a sequence number which can be incremented only by master which is
explicitly acknowledged by slave. Routers also send link state request packets and link state
update packets (which contain the entire LSA) in this state. The contents of the DBD received
are compared to the information contained in the routers link state database to check if new or
more current link state information is available with the neighbor.
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Loading—In this state, the actual exchange of link state information occurs. Based on the
information provided by the DBDs, routers send link state request packets. The neighbor then
provides the requested link state information in link state update packets. During the adjacency,
if a the security appliance receives an outdated or missing LSA, it requests that LSA by sending
a link state request packet. All link state update packets are acknowledged.
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Full—In this state, the neighbors are fully adjacent with each other. All the router and network
LSAs are exchanged and the router databases are fully synchronized.
Full is the normal state for an OSPF router. The only exception to this is the 2-way state, which
is normal in a broadcast network. Routers achieve the full state with their DR and BDR only.
Neighbors always see each other as 2-way.
• Dead Time—Display only. Displays the amount of time remaining that the router waits to receive
an OSPF hello packet from the neighbor before declaring the neighbor down.
• Address—Display only. Displays the IP address of the interface to which this neighbor is directly
connected.