Day 14 - OSPF Operation Flashcards by Houston Molinar

Q

The data portion of an OSPF message is encapsulated in a __________

A

Packet

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Q

In the IP packet header, the protocol field is to set to what number to indicate OSPF?

A

89

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Q

What are the destination multicast addresses for OSPF?

A

224.0.0.5
224.0.0.6

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Q

What are 5 types of OSPF Packets?

A

Hello
DBD
LSR
LSU
LSAck

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Q

Solve for definition of OSPF packet type:

These packets establish and maintain adjacency with other OSPF routers

A

OSPF hello packets

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Q

Solve for definition of OSPF packet type:

This type of packet contains an abbreviated list of the sending router’s link state database. Receiving routers use it to check against the local link-state database

A

DBD (Database Descriptor Packets)

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Q

Solve for definition of OSPF packet type:

Receiving routers can request more information about any entry in the DBD by sending these types of packets

A

Link-state requests

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Q

Solve for definition of OSPF packet type:

These types of packets reply to LSRs and announce new information. These types of packets contain 11 types of LSAs

A

LSU (Link-state updates)

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Q

Solve for definition of OSPF packet type:

When an LSU is received, the router sends this type of packet to confirm receipt of the LSU

A

LSAck

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Q

Full adjacency occurs when two routers have exchanged any necessary __________ and have identical __________ __________?

A

LSUs
Link-state databases

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Q

What types of OSPF packets are used for routing updates?

A

LSUs (Link-state updates)

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Q

What do LSU’s contain within them?

A

LSA (Link-state advertisements)

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Q

An LSU contains one or more what?

A

LSA

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Q

What is the solution to managing the number of adjacencies and the flooding of LSAs on a multiaccess network?

A

Electing a DR and BDR

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Q

The __________ router is responsible for updating all other OSPF routers when a change occurs in the multiaccess network

A

Designated

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Q

All other routers other than DR and BDRs become this

A

DROTHERs

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Q

Each OSPF router maintains a link-state database containing the what received from all other routers

A

LSAs (Link-state advertisements)

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Q

OPSF uses Dijkstra’s algorithm to create a what?

A

An SPF tree

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Q

After the Dijkstra algorithm builds the SPF tree and and calculates cost along each path from source to destination, the SPF tree is then used to populate the what?

A

IP routing table with best possible paths

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Q

True or false:

OSPFv2 and OPSFv3 use a different routing algorithm?

A

False

They both use the Dijkstra SPF algorithm

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Q

True or False:

OSPFv2 and OSPFv3 both use cost as their metric?

A

True

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Q

True or False:

OSPFv2 and OSPFv3 use different packet types

A

False

They both use hello, DBD, LSR, LSU and LSAck packets

Q

True or False:

OSPFv2 and OPSFv3 both use the same function and election process to elect the DR and BDR

A

True

Q

What is the FF02::5 OSPFv3 multicast address used for?

A

All routers multicast

What is the FF02::6 OSPFv3 multicast address used for?

DR/BDR multicast updates

Once adjacencies have been formed, OSPF will then start sending these out

DBD Packets (Database Description Packets)

A router will send out and listen for these when OSPF is enabled on an interface

OSPF Hello Packets

If a router is missing information about any of the networks it received in the DBD, it will send the neighbor one of these

LSR (Link State Request)

These packets contain routing updates

LSA (Link State Advertisement)

These packets contain a list of Link State Advertisements (LSAs) which should be updated and that will be used during flooding

LSU (Link State Update)

This is a routers response to a Link State Request (LSR) asking for more information

Link State Advertisement (LSA)

Scenario: If a new link was added to the network or if a link went down and new information needs to get flooded everywhere so all routers can know about it this type of packet would be processed

LSU (Link State Update)

Receiving routers acknowledge Link State Advertisements (LSA) through these types of packets

LSAck (Link State Acknowledgement)

OSPF sends Hello Packets using Broadcast

False. Hello Packets use Multicast

What are the 6 Steps / Characteristics of OSPF?

1. Discover Neighbors 2. Form Adjacencies 3. Flood the Link State Database 4. Compute the Shortest Path 5. Install the Best Routes Into The Routing Table 6. Respond to Network Changes

What will happen if a router running OSPF has 2 interfaces with different Process IDs?

It will not share information about it's routes with either side of the link due to separate Link State Databases

Does the network command in OSPF default to the classful boundary?

No. That's one of the differences between OSPF and EIGRP

Do you have to enter a wildcard mask in OSPF?

Yes

If a network contained routers with interfaces such as: 10.1.0.1/24 10.0.1.1/24 10.0.2.1/24 And you configured a network command for OSPF as: network 10.0.0.0 0.0.255.255 area 0 What networks would get advertised in the routing table?

10.0.1.0/24 10.0.2.0/24 10.1.0.0 would not be advertised because it doesn't match the 10.0.X.X space that the network command is looking for.

What is the chief characteristic of an ABR?

It separates the LSA Flooding Zones

Routers which have all of their OSPF interfaces in an area and are not in a backbone are considered what?

Normal Area Routers

How do Normal Area Routers learn their routes

From the ABRs

This type of router redistributes routes from different routing protocols into OSPF Normal Area Routers

Autonomous System Boundary Router (ASBR)

What are the general steps for Neighbor State Summary?

1. Down - No active neighbor detected 2. Initilialization - Hello packets sent and received by neighbors 3. 2 WAY - Bi-Directional communication. Can see it's own router ID received in Hello packets 4. Exstart - Primary and secondary roles determined 5. Exchange - DBD packets sent 6. Loading - Exchange of LSRs and LSU (With LSAs within the LSU) 7. Full - Neighbors full adjacent

What is the default Hello interval?

10 Seconds

What is the default Dead interval?

40 Seconds

What settings must be matched for a pair of OSPF routers to form an adjacency?

- They must be in each other's neighbor list - Hello & Dead Intervals - Area ID - IP Subnet - Authentication Flag - Stub Area Flag - MTU and MTU IP Size

What does an OSPF Packet look like?

- Version of OSPF - Packet Type - Packet Length - Router ID - Area ID - Checksum - Auth Type - Authentication - Data

How does a DR get elected?

It has the highest priority. In which case either the Router ID is the highest or it's been manually to set to have a higher OSPF priority on the interface. 1. Manual priority check first 2. Highest configured router id 3. highest loopback address 4. highest IP address

In what OSPF stage do routers get elected?

The Two Way Stage

What the is the default priority on OSPF routers?

1

What states are two DROTHERS considered be in?

A Two Way State

What is a characteristic of link state protocols? classful timer-based routing updates event-triggered routing updates composite metric

event-triggered routing updates