CCNA Day 26 - OSPF

Dijkstra’s Algorithm

Another name for the Shortest Path First algorithm

OSPFv2

Which version of OSPF is usually used for IPv4?

OSPFv3

Which version of OSPF is used for IPv6?

Link State Advertisement

OSPF: What does LSA stand for?

Link State Database

OSPF: What does LSDB stand for?

LSAs

OSPF: What is organized in a structure called the LSDB?

30 minutes

OSPF: What is the default aging timer of LSAs?

Areas

OSPF can divide networks into a separate set of routers and links that share the same LSDB called what?

Backbone Area (Area 0)

OSPF: What area is an area that all other areas must connect to?

Internal Routers

OSPF: Routers with all interfaces in the same area

Area Border Routers (ABRs)

OSPF: Routers with interfaces in multiple areas

2 Areas

OSPF: What is the maximum recommended number of areas that you can connect an ABR to?

Backbone Routers

OSPF: Routers connected to the backbone area (area 0)

Intra-area Route

OSPF: A route to a destination inside the same OSPF area

Interarea Route

OSPF: A route to a destination in a different OSPF area

router ospf [process-id]

Enter OSPF configuration mode:

R1(config)#[…]

network [ip-address] wildcard-mask] area [area]

Enable OSPF on interfaces in the specified range:

R1(config-router)# […]

passive-interface [interface-id]

Prevent an OSPF router from sending OSPF messages out of an OSPF-enabled interface:

R1(config-router)#[…]

default-information originate

Configure an OSPF router to advertise its default route into the OSPF domain:

R1(config-router)#[…]

distance [value]

Modify the OSPF AD on the local router:

R1(config-router)#[…]

maximum-paths [number]

Configure the maximum number of paths an OSPF router will use to perform ECMP load-balancing:

R1(config-router)#[…]

1. Manual Configuration

2. Highest IP address on a loopback interface

3. Highest IP address on a physical interface

What is the OSPF Router ID selection priority?

clear ip ospf process

Reset the OSPF process on the local router:

R1#[…]

Autonomous System Boundary Router (ASBR)

An OSPF router that connects the OSPF network to an external network

No

Does single-area OSPF have to use area 0?

No

Does the OSPF process ID have to match for two routers to become OSPF neighbors?

router-id [a.b.c.d]

Manually configure the OSPF router ID:

R1(config-router)#[…]

Reference bandwidth / interface bandwidth = cost

What is the formula to calculate OSPF interface cost?

100 mbps

What is the default OSPF reference bandwidth?

10

What is the OSPF cost of an Ethernet (10mbps) interface with the default reference bandwidth?

1

What is the OSPF cost of a FastEthernet (100 mbps) interface with the default reference bandwidth?

1

What is the OSPF cost of a Gigabit Ethernet interface with the default reference bandwidth?

1

What is the OSPF cost of a 10Gig Ethernet Interface with the default reference bandwidth?

auto-cost reference-bandwidth [megabits-per-second]

Configure the OSPF reference bandwidth:

R1(config-router)#[…]

1

What is the OSPF cost of a loopback interface?

ip ospf cost [cost]

Configure the OSPF cost of an interface:

R1(config-if)# […]

bandwidth [kilobits-per-second]

Configure the bandwidth of an interface:

R1(config-if)#[…]

No (the speed command does)

Does the bandwidth command change the speed at which an interface operates?

10 seconds

What is the default OSPF Hello timer on an Ethernet connection?

40 seconds

What is the default OSPF Dead timer on an Ethernet connection?

224.0.0.5

What is the multicast address for all OSPF routers?

1. Down

2. Init

3. 2-Way

4. Exstart

5. Exchange

6. Loading

7. Full

What are the OSPF neighbor states?

Down

If no Hello messages have been received, the OSPF neighbor state is […]

Init

If a router receives an OSPF Hello packet but its own router ID is not in the Hello packet, the neighbor state is […]

2-way

When an OSPF router receives a Hello packet with its own router ID, the OSPF neighbor state is […]

2-way

OSPF DR/BDRs are elected in the […] neighbor state

Exstart

In which OSPF neighbor state are a Master and Slave determined?

The router with the higher router ID

In the OSPF Exstart state, which router becomes the master?

The router with the lower router ID

In the OSPF Exstart state, which router becomes the Slave?

Exchange

In which OSPF state do routers exchange DBDs (Database Descriptions) which contain a list of LSAs in their LSDB?

Link State Request

OSPF: What does LSR stand for?

Link State Update

OSPF: What does LSU stand for?

Link State Acknowledgement

OSPF: What does LSAck stand for?

Loading

In what OSPF state do routers send LSR messages to request LSAs from their neighbor?

LSU

What kind of messages are LSAs sent in?

Full

In what OSPF state do routers have a full OSPF adjacency and identical LSDBs?

Hello

OSPF Message Type 1 = […]

Database Description (DBD)

OSPF Message Type 2 = […]

Link-State Request (LSR)

OSPF Message Type 3 = […]

Link-State Update (LSU)

OSPF Message Type 4 = […]

Link-State Acknowledgement (LSAck)

OSPF Message Type 5 = […]

ip ospf [process-id] area [area-id]

Enable OSPF directly on an interface:

R1(config-if)# […]

passive-interface default

Configure all interfaces to be OSPF passive interfaces by default:

R1(config-router)#[…]

Broadcast

OSPF: What network type is enabled on Ethernet and FDDI interfaces by default?

Point-to-point

OSPF: What network type is enabled on PPP and HDLC interfaces by default?

Non-broadcast

OSPF: What network type is enabled on Frame Relay and X.25 interfaces by default?

Yes

In the OSPF Broadcast network type, do routers dynamically discover neighbors?

Yes

In the OSPF Point-to-point network type, do routers dynamically discover neighbors?

No

In the OSPF Non-broadcast network type, do routers dynamically discover neighbors?

Yes

In the OSPF Broadcast network type, are a DR and BDR elected?

No

In the OSPF Point-to-point network type, are a DR and BDR elected?

DROther

OSPF: In the Broadcast network type, routers which aren’t the DR/BDR become a […]

1. Highest OSPF router ID

2. Highest OSPF router ID

What is the OSPF DR/BDR election order of priority?

1

What is the default OSPF interface priority on all interfaces?

the DR and BDR

OSPF DROthers will only move to the Full state with […]

2-Way

OSPF DROthers will remain in the […] neighbor state with other DROthers

224.0.0.6

What address is messages to the OSPF DR/BDR multicast to?

HDLC (cHDLC)

What encapsulation type do serial interfaces use by default?

clock rate [bits-per-second]

Configure the operating speed of a serial interface:

R1(config-if)#[…]

Data Communications Equipment

Serial Connection: What does DCE stand for?

Data Terminal Equipment

Serial Connection: What does DTE stand for?

DCE

Serial Connection: The […] side of the connection specifies the clock rate

encapsulation ppp

Configure the PPP encapsulation on a serial interface:

R1(config-if)#[…]

show controllers [interface-id]

Which command can be used to check if a serial interface is DCE or DTE?

ip ospf network [type]

Configure the OSPF network type of an interface:

R1(config-if)#[…]

Hello: 30 seconds

Dead: 120 seconds

What is the default Hello and Dead timers for OSPF Non-broadcast network type?

shutdown

Disable the OSPF process on the router:

R1(config-router)#[…]

No

Can routers with matching OSPF router IDs become neighbors?

Yes

Do OSPF Hello and Dead timers have to match for routers to become OSPF neighbors?

ip ospf authentication

Enable OSPF authentication on an interface:

R1(config-if)#[…]

ip ospf authentication-key [password]

Configure an OSPF password on an interface:

R1(config-if)#[…]

Full State

If the IP MTU settings on the interfaces don’t match, routers can become OSPF neighbors but wont move to the […] state.

Learn OSPF routes

If two routers have an OSPF network type mismatch, they will form an OSPF adjacency but won’t […]

Router LSA

OSPF Type 1 LSA

Network LSA

OSPF Type 2 LSA

AS-External LSA

OSPF Type 5 LSA