7.1 Open Shortest Path First (OSPF) Overview Flashcards
What size of network is the OSPF (Open Shortest Path First) protocol suitable for
Large networks
What is Link-State Routing Protocol
A set of rules the router uses to obtain information about neighboring routers and the state of their links.
What is Hello packets
Messages that are sent out and received by OSPF routers. These messages are used to establish adjacencies. Adjacencies are also referred to as neighbor relationships.
What is Link-State advertisements (LSA)
Messages that routers send out to routers within their own areas. LSAs include the routing topology of local routers.
What is Link-state database
Data stored in each OSPF router that contains a global view of every link in the autonomous system.
What routers do OSPF routers share information with
only adjacent routers
What conditions must be met before two routers become fully adjacent
Both routers must be on the same subnet and use the same subnet mask.
Both routers must have the same hello and dead intervals configured.
Both routers must use the same OSPF area.
If authentication is required, both routers must pass the authentication requirements.
The stub area flag (value) for each router must match.
Describe Designated Router (DR)
On each subnet, one OSPF router is chosen as the DR. The DR coordinates the routing table updates for all routers on the subnet:
Other routers send information to the DR.
The DR manages the changes and forwards any necessary information to the other routers on the subnet.
Describe Backup Designated Router (BDR)
On each subnet, a single OSPF router is identified as the BDR. The BDR becomes the DR if the DR becomes unavailable.
What areas used for
To subdivide a large network
Describe Area border routers (ABR)
Routers on the edge of areas that share summarized information between areas
Describe Backbone
Is a specialized area connected to all other areas.
Contains networks not held within another area and distributes routing information between areas.
Has an address of 0.0.0.0.
Is required on all OSPF networks.
Describe Stub
An area with a single path into and out of the area.
If you configure a passive interface in OSPF, the interface:
Won't send hello messages. Ignores received hello messages. Won't form adjacencies (neighbor relationships). Won't send or receive LSAs. Won't build routing tables.
There are times when a passive interface is the best choice. For example, when:
OSPF is running on a low-bandwidth connection.
OSPF updates are traversing the WAN.
The connection between routers is being serviced by a static route. Static routes don’t need OSPF running across the link.
