Chapter 8-10 OSPF

What is the LSA age field in the LSDB used for?

Troubleshoot when was the last time an LSA was advertised

TRUE OR FALSE All routers within the same OSPF area maintain an identical copy of the link-state database (LSDB).

True

True or False The area ID can be configured with simple decimal and dotted decimal?

True

True or false: Breaking a large OSPF topology into smaller OSPF areas can be considered a form of summarization.

True

What type of hierarchical tier does OSPF uses ?

Two-Tier hierarchical achitecture

Name all six IPV4 routing LSA types

Type 1, Router LSA Type 2, network LSA Type 3, summary LSA Type 4, ASBR summary LSA Type 5, AS external LSA Type 7, NSSA external LSA

Which LSA advertises the LSAs that originate within an area

Type 1, router LSA

Which LSA advertises a multi-access network segment attached to a DR

Type 2, network LSA

Which LSA advertises network prefixes that originated from a different area

Type 3, summary LSA

Which LSA advertises a summary LSA for a specific ASBR

Type 4, ASBR summary LSA

Which LSA advertises LSAs for routes that have been redistributed

Type 5, AS external LSA

Which LSA advertises redistributed routes in NSSAs

Type 7, NSSA external LSA

What happens within a OSPF area if a topology change occurs such as a link flap or an additional network being added within an area?

All routers in the same OSPF area calculate the SPF tree again.

Why is simplifying an OSPF topology with areas so important?

Because the larger the network gets, the more convergence, and resources is used to maintain the network by using areas it can simplify a OSPF topology while still connecting networks together

Why does OSPF does not put the DR functionality on Point to Point networks

Because this networks only two nodes can exist in a point to point network

How is an ospf router is able to determine where the Dr and BDR are?

By sending an LSA to the ALLDRouter 224.0.0.6 Multicast address

How is the process of summarizing routes on an OSPF router accomplished?

By using the OSPF process configuration command area area-id range network subnet-mask

What is the OSPF logic when selecting which router will be the DR or BDR?

1 - Highest OSPF Priority 2 - Highest Router ID

What is the logic behind OSPF routers selecting a router ID automatically?

1- The highest IP address of any up loop back interfaces. 2- The Highest IP address of any active physical interfaces

What is the advertised network for the loopback interface with IP address 10.123.4.1/30?

10.123.4.1/32

OSPF automatically assigns a link cost to an interface based on a reference bandwidth of ___________.

100 Mbps

What is the default reference bandwidth in OSPF?

100 Mbps

What OSPF neighbor state indicates Bidirectional communication has been established. If a DR or BDR is needed, the election occurs during this state.

2-way

What are the two Multicast addresses and mac addresses use in OSPF?

224.0.05 01:00:5E:00:00:05 224.0.0.6 01:00:5E:00:00:06

OSPF uses the protocol number ___________ for its inter-router communication.

89

What command restarts the ospf process?

Clear ip ospf process

What formula is used for OSPF link cost?

Cost = Reference Bandwidth / Interface Bandwidth

These packets are for summarizing database contents. Packets are exchanged when an OSPF adjacency is first being formed. These packets are used to describe the contents of the LSDB.

Database description (DBD) or DDP

Usually the Wait timer has the same time as the ?

Dead timer interval

What algorithm is used in OSPF?

Dijkstra Shortest Path First algorithm

What OSPF neighbor state indicates that the router has not received any OSPF hello packets.

Down

Special area called the backbone

Area 0

OSPF routers connected to Area 0 and another OSPF are

Area Border Routers

What OSPF neighbor state relevant to NBMA networks that do not support broadcast and require explicit neighbor configuration. This state indicates that no information has been received recently, but the router is still attempting communication.

Attempt

Why is it important to set the dead intervals longer then the hello timer?

Because so that the dead interval timer does not reach 0 between hello packets

When running multiple ospf processes what is important to keep in mind in regards to the redistribution of router?

Each process has a unique database and the routes learned in one Processes are not available to a different OSPF processes without redistribution of orutes between processes

What OSPF neighbor state is the first state in forming an adjacency. Routers identify which router will be the master or slave for the LSDB synchronization.

ExStart

What OSPF neighbor state indicates routers are exchanging link states by using DBD packets.

Exchange

A member router contains a complete copy of the LSDBs for every area in the routing domain

False

A router with an interface associated with Area 1 and Area 2 will be able to inject routes learned from one area into another area

False

TRUE OR FALSE Can a interface belong to more than one Area in OSPF?

False

True or False each router sees itself as the lowest of the Shortest Path First TREE?

False

True or false: A default route advertised with the command default information-originate in OSPF will always appear as an OSPF inter-area route.

False

True or false: OSPF is only enabled on a router interface by using the command network ip-address wildcard-mask area area-id under the OSPF router process.

False

True or false: OSPF uses the shortest total path metric to identify the best path for every internal OSPF route (intra-area and interarea).

False

True or false: The OSPF process ID must match for routers to establish a neighbor adjacency.

False

True or false: The router with the highest IP address is the designated router when using a serial point-to-point link

False

When an ABR receives a network LSA, the ABR forwards the network LSA to the other connected areas.

False

True of False is required to set the same bandwidth reference on all routers participating on an OSPF domain?

False, is good practice to place the same reference bandwidth

True or False As an OSPF router adds or removes a directly connected network link to or from its database, the router floods the link-state advertisement (LSA) out all active and inactive OSPF interfaces.

False, only active OSPF interfaces

True or False: All routers from different areas have the same LSDB?

False, only routers within the same area do have the same LSDB

OSPF uses ___________ packet types for inter-router communication.

Five

What OSPF neighbor state indicates Neighboring routers are fully adjacent.

Full

These packets are for discovering and maintaining neighbors. Packets are sent out periodically on all OSPF interfaces to discover new neighbors while ensuring that other adjacent neighbors are still online.

Hello

What are the five different packet types in OSPF?

Hello Database description (DBD) or DDP Linkstate request (LSR) Link-state update (LSU) Link-state ack

What command turns on the OSPF network on a loopback

IP OSPF NETWORK POINT-TO-POINT

What destination addresses does OSPF use, when feasible? (Choose two.) A - IP address 224.0.0.5 B- IP address 224.0.0.10 C- IP address 224.0.0.8 D- MAC address 01:00:5E:00:00:05 E- MAC address 01:00:5E:00:00:0A

IP address 224.0.0.5 MAC address 01:00:5E:00:00:05

Which multicast address is used for ALLDRouters

IPv4 224.0.0.6

Which multicast address is used for ALLSPFROUTERS?

IPv4 address 224.0.05

How many fields are inside a hello packet in OSPF?

NINE

Can you see the exact topology from one area to another outside area?

No your only able to the necessary information to be able to communicate to an outside area

in OSPF what is a logical grouping of routers or, more specifically

OSPF Area

What OSPF neighbor state indicates that a hello packet has been received from another router, but bidirectional communication has not been established.

Init

When a type 3 LSA is received in a nonbackbone area, what does the ABR do?

Installs the type 3 LSA for only the area where it was received

All areas in OSPF inject routing information into which area?

Into the backbone area 0

Network routes that are learned from other OSPF routers within the same area

Intra-Area Routes

What is the backbone AREA in charged of?

It distrutes routes of different areas so that different areas can communicate

What is the OSPF network type loopback feature?

It states that the IP address is always advertise a /32 prefix on a loopback interface even if the interface does not have an actual /32 prefix

How does OSPF sends to neighboring routers advertisements that contain link state and metric

Link State Advertisements (LSAs)

What is the database used by ospf neighbors to keep all advertised LSAs?

Link State Database LSDB

These packets are for flooding acknowledgments. These packets are sent in response to the flooding of LSAs, thus making flooding a reliable transport feature.

Link-state ack

These packets are for database downloads. When a router thinks that part of its LSDB is stale, it may request a portion of a neighbor's database by using this packet type

Link-state request (LSR)

These packets are for database updates. This is an explicit LSA for a specific network link and normally is sent in direct response to an LSR.

Link-state update (LSU)

What OSPF neighbor state indicates LSR packets are sent to the neighbor, asking for the more recent LSAs that have been discovered (but not received) in the Exchange state.

Loading

In order for an OSPF neighbor successfully become adjacent with is neighbors what requirements must it pass?

RIDs must be unique Interfaces must share a common subnet MTUs must match in the interface Area ID must match The Designated Router enablement must match OSPF hello and dead timer must match Authentication type and credentials must match Area type flags must match for segment

What are the benefits from segmenting OSPF domains into multiple areas?

Reduces the size of the LSDB for each area, SPF tree calculations become faster, and decreasing LSDB flooding between routers when a link flap occurs

Which LSA type exists in all OSPF areas?

Router

What are the 9 fields within a OSPF hello packet?

Router ID Authentication options Area ID Interface address mask interface priority Hello Interval Dead Interval Designated Router and Designated Backup routers Active Neighbor

What happens outside a OSPF area if a topology change occurs such as a link flap or an additional network being added within an area?

Routers outside that area do not calculate the full SPF tree again but perform a partial SPF calculation if the metric have changed or prefix is removed

What networks are set to Point to point on OSPF by default

Serial interfaces, GRE tunnels and Frame Relays

What type of network circuits dont need a Designated router?

Serial links

OSPF supports filtering of routes using what techniques?

Summarization, using the no-advertise option Area filtering, which prevents type 1 LSAs from being generated into a type 3 LSA

Explain the purpose for the DEADTimer

The Dead timer is used to determine the time when the neighboard has not check in and if the neighbor does not check in it will reconverge the network

To ensure that all routers have fully initialized which packet initiates a wait timer when OSPF hello timers do not contain a DR/BDR router for a segment?

The Wait timer

A special area in OSPF that every other area must connect to?

The backbone area or Area0

Explain the purpose for the Hello Timer

The hello packet intervals are used to discover and update router status

What command is configured to prevent a router from becoming the designated router for a network segment?

The interface command ip ospf priority 0

If a hybrid configuration of OSPF exist on a router meaning there is a network statement configuration and an interface specific configuration which configuration takes precedence over the other?

The interface specific

What can be build from the LSDB?

a topology of the advertised network

What command changes the bandwidth referene in ospf?

auto-cost reference-bandwidth

How is OSPF able to provide scalability?

by using Areas

What command sets up the default route in OSPF?

default-information originate

How many OSPF link-state announcement (LSA) types are used for routing traditional IPv4 packets?

five

Network routes that are learned from other OSPF routers from a different area using an ABR are known as

interarea routes

What command configures ospf on the interface configuration mode?

ip ospf 1 area

What command modifies the priority for ospf and where would this command be executed from?

ip ospf priority [0-255] within the interface configuration mode

What is the formula to find the number of adjecencies?

n(n-1)/2

What command enables OSPF on all interfaces?

network 0.0.0.0 255.255.255.255 area 0

What command verifies OSPF timers

show ip ospf interface

What command best shows the OSPF interface role in a router?

show ip ospt interface brief