OSPF LSAs Flashcards
Name the six IPv4 LSA types.
1 - router, 2 - network, 3 - network summary, 4 - ASBR summary, 5 - AS external, 7 - NSSA external
What type of OSPF packet contains LSAs?
Link State Update (LSU)
What information does a type 1 LSA contain and where is it shared?
A type 1 router LSA contains all the information about a router’s attached links and is flooded to all routers in the area.
What value is used for the link state identifier (LSID) field in type 1 advertisements?
Type 1 router LSAs use the source router’s router-id in the link state id field.
Give the command for showing all type 1 LSAs from router 1.1.1.1.
sh ip ospf database router adv-router 1.1.1.1
As a rule of thumb, areas should contain no more than what number of routers?
40
What four types are advertised in type 1 LSAs?
Type 1 router LSAs can be “stub,” “transit network”, “another router (point-to-point)” or virtual links.
What are in the link id and link data fields for a “stub” network in a type 1 router LSA?
Link id: network
Link data: netmask of the interface
What are in the link id and link data fields for a “transit network” in a type 1 router LSA?
Link id: DR’s IP address
Link data: router’s IP address on the link
What are the link id and link data fields for a “router (point-to-point)” network in a type 1 router LSA?
Link id: neighboring router ID
Link data: router’s IP address on the link
Then, a second entry is appended, using the same link but as a stub network.
Link id: network
Link data: netmask of the interface
What are the link id and link data fields for a “virtual link” network in a type 1 router LSA?
Link id: neighboring router ID
Link data: router’s IP address on the link
How are point-to-multipoint and loopback IP addresses advertised?
As /32 host addresses
What is the maximum amount of time an LSA remains valid?
1 hour (3,600 seconds)
How is information poisoned in OSPF?
By sending an LSA with the age set to the maximum time
Which links are advertised as /32 host addresses by default?
Point-to-multipoint and loopbacks
How can a loopback address be sent with the full subnet mask?
Set the loopback as a point-to-point link.
interface Loopback0
ip ospf network point-to-point
What is a type 1 LSA?
Type 1 router LSA
What is a type 2 LSA?
A type 2 network LSA is sent by a DR on multiaccess networks advertising the subnet, mask, and all neighbor router-ids in the network.
What does a type 3 LSA include?
A type 3 summary LSA includes the subnet and mask, with the advertising router set as the ABR’s router-id.
How do other routers learn a router is an ABR or ASBR?
The flags are present in the type 1 router LSAs
What type of LSA do area border routers send?
type 3 summary LSA
Give the command to view all type 3 LSAs.
sh ip ospf database summary
How often do routers flood type 1 LSAs if there are no changes?
Every thirty minutes they flood and reset the timer.
Is a type 3 LSA flooded through an ABR?
Technically the ABR will create its own new type 3 LSA.
What is a type 5 LSA?
A type 5 external LSA is created by an ASBR.
What are the LSID and data fields in a type 5 LSA?
The LSID in a type 5 external LSA is the subnet, and the data field contains the mask.
What is the default cost for a type 5 LSA?
1
What are the two sub-types for type 5 LSAs? Which is the default?
Subtype 1, where receiving routers calculate their own additional costs to get to the ASBR, and subtype 2, where they do not. Subtype 2 is the default.
Which routers receive type 5 LSAs?
Type 5 LSAs are flooded to all of the routers in the domain, except stub areas.
What type of LSA is sent into stub areas as a default route and what is the default metric?
A type 3 summary LSA with a metric of one.
Which kinds of LSAs do stub routers not receive?
They do not receive type 5 external network LSAs and may or may not receive type 3 LSAs, depending on the stub type.
Which type of LSAs do not show under a specific area with “sh ip ospf database”?
type 5 external LSAs
What is a type 7 LSA?
A type 7 NSSA external LSA is sent by ASBRs in a not-so-stubby area.
Where are type 7 LSAs flooded?
Type 7 NSSA external LSAs are flooded to all routers in the domain, except they are changed into a type 5 external LSA at the first ABR they hit.
What are the two subtypes for type 7 LSAs? Which is the default?
Sub-type 1 increments the router’s cost to get to the ASBR to the LSA’s cost. Sub-type 2 (the default) does not.
What is the default metric for a type 7 LSA?
20
