Chapter 8 - Single-Area OSPF

Fast Convergence

Activity 1 - Matching : Part 1 (Identifying OSPF Features) Quickly propagates network changes.

Secure

Activity 1 - Matching : Part 1 (Identifying OSPF Features) Support MD5 authentication

Classless

Activity 1 - Matching : Part 1 (Identifying OSPF Features) Supports VLSM and CIDR.

Link-State Database

Activity 1 - Matching : Part 2 (Identifying OSPF Terminology) Creates the topology table

Adjacency Database

Activity 1 - Matching: Part 2 (Identifying OSPF Terminology) Creates the neighbor table

Dijksta's Algorythm

Activity 1 - Matching: Part 2 (Identifying OSPF Terminology) Used to compute SPF cost

Link-State Requests (LSR)

Activity 2 - Matching: Part 1 (Identifying OSPF Packet Types) Asks for specific link-state records from router to router.

Hello

Activity 2 - Matching: Part 1 (Identifying OSPF Packet Types) Discovers neighbors and builds adjacencies between them.

Link-State Update (LSU)

Activity 2 - Matching: Part 1 (Identifying OSPF Packet Types) Sends specifically requested link-state records

Database Description (DBD)

Activity 2 - Matching: Part 2 (Identifying OSPF Packet Types) Checks for database synchronization between routers.

Link-State Acknowledgement (LSAck)

Activity 2 - Matching: Part 2 (Identifying OSPF Packet Types) Confirms receipt of a link-state update packet.

Hello.

Activity 2 - Matching: Part 2 (Identifying OSPF Packet Types) Maintains adjacency with other OSPF routers.

Init State.

Activity 3 - Matching: Part 1 (Identifying the OSPF State for Establishing Adjacency) Hello packets are received from neighbors, containing the sending Router ID.

Ex-Start State.

Activity 3 - Matching: Part 1 (Identifying the OSPF State for Establishing Adjacency) Initiates the exchange of DBD packets.

Two-Way State.

Activity 3 - Matching: Part 1 (Identifying the OSPF State for Establishing Adjacency) On Ethernet links, elect a Designated Router (DR) and a Backup Designated Router (BDR).

Exchange State.

Activity 3 - Matching: Part 1 (Identifying the OSPF State for Establishing Adjacency) Routers Exchange DBD packets.

Ex-Start State.

Activity 3 - Matching: Part 2 (Identifying the OSPF State for Establishing Adjacency) Negotiate master/slave relationship and DBD packet sequence number.

Down State.

Activity 3 - Matching: Part 2 (Identifying the OSPF State for Establishing Adjacency) No Hello packets received.

Full State.

Activity 3 - Matching: Part 2 (Identifying the OSPF State for Establishing Adjacency) Routers have converged.

Loading State.

Activity 3 - Matching: Part 2 (Identifying the OSPF State for Establishing Adjacency) Routes are processed using the SPF algorithm.

Create adjacencies with neighbors Exchange routing information Calculate the best routes Reach convergence

An OSPF router attempts to do what four things when initially connected to a network?

Down State --> Init State --> Two-Way State

During the 'Establish Neighbor Adjacencies' phase, what three Operational States does OSPF move through?

ExStart State --> Exchange State --> Loading State

During the 'Sychonize OSPF Databases' phase, what three Operations States does OPSF move through?

89

In the IPv4 Packet Header's protocol field, what code is used for OPSF?

AD 110

OSPF has an Administrative Distance of what?

False. The difference between the LSU and LSA terms can sometimes be confusing because these terms are often used interchangeably. However, an LSU contains one or more LSAs.

The difference between the LSU and LSA terms can sometimes be confusing because these terms are often used interchangeably. True or False An LSU is, therefore, indistinguishable from an LSA.

True. OSPFv3 has similar packet types. Each packet serves a specific purpose in the OSPF routing process.

True of False OSPFv2 uses five different types of LSPs.

False After the topological databases are synchronized, updates (LSUs) are sent to neighbors when a change is perceived, and every 30 minutes.

True or False After the topological databases are synchronized, updates (LSUs) are sent only to neighbors when a change is perceived.

False. A Type 3 LSR packet is used by the receiving routers to request more information about an entry in the DBD. Type 4 packets are LSU and is used to reply to an LSR packet.

True or False A Type 4 LSR packet is used by the receiving routers to request more information about an entry in the DBD.

True. LSUs are also used to forward OSPF routing updates, such as link changes.

True or False A Type 5 packet is used to acknowledge the receipt of a Type 4 LSU.

True

True or False As long as the neighboring routers continue receiving Hello packets, the network in transmitted LSAs remain in the topology database.

True.

True or False By default, the formula used to calculate OSPF cost is; Cost = 100,000,000 bps / interface bandwidth in bps

False. Cisco uses a default of 4 times the Hello interval: 40 seconds (default on multiaccess and point-to-point networks) 120 seconds (default on NBMA networks; for example, Frame Relay)

True or False Cisco uses a default of 3 times the Hello interval: 30 seconds (default on multiaccess and point-to-point networks) 90 seconds (default on NBMA networks; for example, Frame Relay)

True. This means that the interface address does not need to be included in one of the OSPF network commands for the router to use that IPv4 address as the router ID. The only requirement is that the interface is active and in the up state.

True or False If the router uses the highest IPv4 address for the router ID, the interface does not need to be OSPF-enabled.

True. As with reference bandwidth, interface bandwidth values do not actually affect the speed or capacity of the link. Instead, they are used by some routing protocols, like OSPF, to compute the routing metric. Therefore, it is important that the bandwidth value reflects the actual speed of the link so that the routing table has accurate best path information.

True or False In OSPF, all interfaces have default bandwidth values assigned to them.

True.

True or False Layer 3 devices (such as routers) running OSPF exchange messages to convey routing information using five types of packets.

False. OSPF has a lower number (making it a preferred routing protocol over IS-IS and RIP) on Cisco devices.

True or False OSPF has a higher Administrative Distance than both IS-IS and RIP routing protocols on Cisco devices.

True.

True or False OSPF uses cost as a metric. A lower cost indicates a better path than a higher cost.

False. OSPF uses link-state packets (LSPs) to establish and maintain neighbor adjacencies and exchange routing updates.

True or False OSPF uses distance-vector packets (DVPs) to establish and maintain neighbor adjacencies and exchange routing updates.

False OSPFv2 is classless by design; therefore, it supports IPv4 VLSM and CIDR.

True or False OSPFv2 does not support IPv4 VLSM and CIDR.

True. OSPFv3 also uses the SPF algorithm as the computation engine to determine the best paths throughout the routing domain.

True or False OSPFv3 has the same functionality as OSPFv2, but uses IPv6 as the network layer transport, communicating with OSPFv3 peers and advertising IPv6 routes.

False. On Cisco routers, the default bandwidth on most serial interfaces is set to 1.544 Mb/s.

True or False On Cisco routers, the default bandwidth on most serial interfaces is set to 100 Mb/s.

True. These are an abbreviated list of the sending router's LSDB and is used by receiving routers to check against the local LSDB.

True or False Routers initially exchange Type 2 DBD packets.

True. If the Dead interval expires before the routers receive a Hello packet, OSPF removes that neighbor from its LSDB. The router floods the LSDB with information about the down neighbor out all OSPF-enabled interfaces.

True or False The Dead interval is the period that the router waits to receive a Hello packet before declaring the neighbor down.

False. The Forwarding Database creates and maintains the Routing Table.

True or False The Forwarding Database creates and maintains the Neighbor Table.

True.

True or False The Link-state Database (LSDB) creates and maintains the Topology Table.

True.

True or False The Neighbor Table, Topology Table, and Routing table are all stored in RAM.

True. More overhead and time delays equal a higher cost. Therefore, a 10-Mb/s Ethernet line has a higher cost than a 100-Mb/s Ethernet line.

True or False The cost of an interface is inversely proportional to the bandwidth of the interface. Therefore, a higher bandwidth indicates a lower cost.

False. The default reference bandwidth is 10^8 (100,000,000)

True or False The default reference bandwidth is 10^6

False. The process_ID value following the ISO command 'router ospf (process_ID)' is selected by the network administrator.

True or False The process_ID value following the ISO command 'router ospf (process_ID)' is determined by the router model number running OSPF.

False. The process_ID value following the ISO command 'router ospf (process_ID)' represents a number between 1 and 65, 535.

True or False The process_ID value following the ISO command 'router ospf (process_ID)' represents a number between 1 and 4,096.

False. They contain lists of neighboring routers with which to exchange information.

True or False The three Databases used to maintain Tables by OSPF contain lists of neighboring switches with which to exchange information.

False. OSPF progresses through several states while attempting to reach convergence.

True or False When attempting to reach convergence, OSPF remains in the Down State.

False. When encapsulating an Ethernet frame, OSPFv2 identifies one of two multicast MAC addresses as its destination MAC.

True or False When encapsulating an Ethernet frame, OSPFv2 identifies a unicast MAC address as its destination MAC.

True.

True or False When encapsulating an IPv4 packet, OSPFv2 identifies one of two multicast IP addresses as the destination IP.

False. The cost of an OSPF route is the accumulated value from one router to the destination network.

True or False. The cost of an OSPF route is the highest value from one router to the destination network.

True. This means that it does not have to be the same value on the other OSPF routers to establish adjacencies with those neighbors.

True or False. The process-id value is locally significant.

Hello packet

Types of OSPF Packets What is OSPF Packet - Type 1

Database Description (DBD) packet

Types of OSPF Packets What is OSPF Packet - Type 2

Link-State Request (LSR) packet

Types of OSPF Packets What is OSPF Packet - Type 3

Link-State Update (LSU) packet

Types of OSPF Packets What is OSPF Packet - Type 4

Link-State Acknowledgment (LSAck) packet

Types of OSPF Packets What is OSPF Packet - Type 5

router ospf (process_ID)

What IOS command, entered in global configuration mode, will enable OSPFv2?

No Hello packets receives = Down. Router sends Hello packets. Transition to Init State.

What are the characteristics of the OSPF Operations State called 'Down State?'

Negotiate master / slave relationship and DBD packet sequence number. The master initiates the DBD packet exchange.

What are the characteristics of the OSPF Operations State called 'ExStart State?'

Routers echange DBD packets. If additional router information is required then transition to Loading; otherwise, transition to the Full State.

What are the characteristics of the OSPF Operations State called 'Exchange State?'

Routers have converged.

What are the characteristics of the OSPF Operations State called 'Full State?'

Hello packets are received from the neighbor. They contain the sending router's Router ID. Transition to Two-Way State.

What are the characteristics of the OSPF Operations State called 'Init State?'

LSRs and LSUs are used to gain additional route information. Routes are processed using the SPF algorithm. Transition to the Full State.

What are the characteristics of the OSPF Operations State called 'Loading State?'

On Ethernet links, elect a DR, and a BDR. Transition to ExStart State.

What are the characteristics of the OSPF Operations State called 'Two-Way State?'

Classess Efficient Fast Convergence Scalable Secure

What are the five 'Features of OSPF,' as given by the curriculum?

Hello packet Database description packet Link-state request packet Link-state update packet Link-state acknowledgment packet

What are the five types of packets exchanged by Layer 3 devices (such as routers) running OSPF, according to the curriculum?

Router ID explicitly configured. IPv4 loopback interface configured. Highest active configured IPv4 address on the device.

What is the 'Router ID Order of Precedence?'

Cost = reference bandwidth / interface bandwidth

What is the formula used to calculate OSPF cost metric?

10 seconds (default on multiaccess and point-to-point networks) 30 seconds (default on non-broadcast multiple access [NBMA] networks; for example, Frame Relay)

What is the frequency with which Hello Packets are sent by OSPF?

Contains an abbreviated list of the sending router's LSDB and is used by receiving routers to check against the local LSDB. The LSDB must be identical on all link-state routers within an area to construct an accurate SPF tree.

What is the use of an OSPF Database Description (DBD) packet?

Used to establish and maintain adjacency with other OSPF routers.

What is the use of an OSPF Hello packet?

When an LSU is received, the router sends an LSAck to confirm receipt of the LSU. The LSAck data field is empty.

What is the use of an OSPF Link-State Acknowledgment (LSAck) packet?

To allow receiving routers the ability to request more information about any entry in the DBD.

What is the use of an OSPF Link-State Request (LSR) packet?

Used to reply to LSRs and to announce new information. LSUs contain seven different types of LSAs.

What is the use of an OSPF Link-State Update (LSU) packet?

Adjacency Database Link-state Database (LSDB) Forwarding Database

What three databases are created and maintained by OSPF according to the cirriculum?

The Route ID is used to Uniquely Identify the Router. The Route ID is used to Participate in the Election of the DR.

What two action are performed using the Router ID of an OSPF-enabled router?

The Adjacency Database.

Which Database creates and maintains the Neighbor Table?

Full State

Which OSPF Operations State follows the Loading State?

OSPF Packet Type Router ID Area ID

Which three pieces of data are contained within the OSPF Packet Header?

224.0.0.5 or 224.0.0.6

Which two multicast IP addresses are used by OSPFv2 to serve as the destination IP for encapsulated IPv4 packets?

01-00-5E-00-00-05 or 01-00-5E-00-00-06

Which two multicast MAC addresses are used by OSPFv2 to serve as the destination MAC for encapsulated Ethernet frames?