OSPF LSAs Flashcards Preview

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Flashcards in OSPF LSAs Deck (36):
1

Name the six IPv4 LSA types.

1 - router, 2 - network, 3 - network summary, 4 - ASBR summary, 5 - AS external, 7 - NSSA external

2

What type of OSPF packet contains LSAs?

Link State Update (LSU)

3

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.

4

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.

5

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

6

As a rule of thumb, areas should contain no more than what number of routers?

40

7

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.

8

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

9

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

10

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

11

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

12

How are point-to-multipoint and loopback IP addresses advertised?

As /32 host addresses

13

What is the maximum amount of time an LSA remains valid?

1 hour (3,600 seconds)

14

How is information poisoned in OSPF?

By sending an LSA with the age set to the maximum time

15

Which links are advertised as /32 host addresses by default?

Point-to-multipoint and loopbacks

16

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

17

What is a type 1 LSA?

Type 1 router LSA

18

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.

19

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.

20

How do other routers learn a router is an ABR or ASBR?

The flags are present in the type 1 router LSAs

21

What type of LSA do area border routers send?

type 3 summary LSA

22

Give the command to view all type 3 LSAs.

sh ip ospf database summary

23

How often do routers flood type 1 LSAs if there are no changes?

Every thirty minutes they flood and reset the timer.

24

Is a type 3 LSA flooded through an ABR?

Technically the ABR will create its own new type 3 LSA.

25

What is a type 5 LSA?

A type 5 external LSA is created by an ASBR.

26

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.

27

What is the default cost for a type 5 LSA?

1

28

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.

29

Which routers receive type 5 LSAs?

Type 5 LSAs are flooded to all of the routers in the domain, except stub areas.

30

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.

31

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.

32

Which type of LSAs do not show under a specific area with "sh ip ospf database"?

type 5 external LSAs

33

What is a type 7 LSA?

A type 7 NSSA external LSA is sent by ASBRs in a not-so-stubby area.

34

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.

35

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.

36

What is the default metric for a type 7 LSA?

20