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Cisco CCNA 3/3: Enterprise Networking, Security, and Automation v7 > Chapter 1 - Single Area OSPFv2 Concepts > Flashcards

Chapter 1 - Single Area OSPFv2 Concepts Flashcards

1
Q

OSPFv2 is for…

OSPFv3 is for…

A

…IPv4

…IPv6

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2
Q

What protocol is a link state protocol developed as an alternative for the distance vector RIP? It offers faster convergence and scales well.

A

OSPF

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3
Q

what is used to determine best path to destination in OSPF

A

Cost

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4
Q

OSPF link-state info includes:

A

network prefix, prefix length and cost

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5
Q

What 5 packet types does OSPF use to convey routing info and used to discover neighboring routing and exchange routing info to maintain accurate info about the network?

A
  • Hello Packet
  • Database Description (DBD) Packet
  • Link-State Request (LSR) Packet
  • Link-State Update (LSU) Packet
  • Link-State Acknowledgement (LSA) Packet
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6
Q

OSPF messages are used to create and maintain 3 OSPF databases, what are they and what is created

A
  • Adjacency Database - creates the neighbor table
  • Link-State Database - creates the topology table
  • Forwarding Database - creates the routing table
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7
Q

which OSPF database lists all neighbor routers that established bidirectional communication?
What CLI command is used to see this database?

A

Adjacency Database

show ip ospf neighbor

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8
Q

which OSPF database represents the network topology?

What CLI command is used to see this database?

A

Link-State Database (LSDB)

show ip ospf database

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9
Q

what OSPF database contains the list of routes that is generated when an algorithm is run on the link-state database?
What CLI command is used to see this database?

A

Forwarding Database

show ip route

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10
Q

What algorithm is the topology table built through?

A

Dijkstra Shortest-path First (SPF) - cumulative cost to reach a destination

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11
Q

Link-State routing steps completed by a router: Step 1. Establish Neighbor Adjacencies

A

OSPF-enabled router sends HELLO packets out on all OSPF-enabled interfaces to see if neighbors are present on those links. If yes, router attempts to establish neighbor adjacencies with that neighbor

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12
Q

Link-State routing steps completed by a router: Step 2. Exchange Link-State Advertisements (LSA)

A

After neighbor adjacencies are established, routers exchange LSA - contains state and cost of each directly connected link. Neighbors receiving LSA immediately flood the LSA to other directly connected neighbors.

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13
Q

Link-State routing steps completed by a router: Step 3. Build the Link State Database (LSDB)

A

LSDB is built based on LSA received

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14
Q

Link-State routing steps completed by a router: Step 4. Execute SPF Algorithm

A

SPF algorithm creates the SPF tree that is used to calculate the shortest path to each node

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15
Q

Link-State routing steps completed by a router: Step 5. Choose the Best Route

A

Best paths to each network are offered to IP routing table. Routing decisions are made based on entries in routing table

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16
Q

what is a group of routers that share the same link-state info in their LSDBs?

A

OSPF area

17
Q

multiarea OSPF vs single-area OSPF

A
  • single-area: all routers in one area (use area 0)
  • multiarea: OSPF is implemented using multiple areas, in a hierarchical fashion; but all areas are connected by a backbone area.
18
Q

Hierarchical-topology design option advantages to multiarea OSPF:

A
  • smaller routing tables
  • reduced link-state update overhead
  • reduced frequency of SPF calculations
19
Q

what are area border routers

A

routers that interconnect areas in a multiarea OSPF implementation

20
Q

what is OSPFv3 Address Families feature

A

it includes support for both IPv4 and IPv6

21
Q

Tools used by OSPF to help determine the fastest available route for a pakcet

A

link-state packets

22
Q

purpose of Hello Packet

A
  • establish and maintain adjacency with other OSPF routers
  • advertise parameters on which two routers must agree to become neighbors
  • elect the Designated Router (DR) and the Backup Designated Router (BDR)
23
Q

purpose of Database Description Packet

A

contains abbreviated list of LSDB of the sending router and is used by receiving routers to check against local LSDB.

LSDB must be identical on all link-state routers within an area to construct accurate SPF tree

24
Q

purpose of Link-State Request (LSR) packet

A

receiving routers use to request more info about any entry in the DBD

25
Q

purpose of Link-State Update (LSU) packet

A

used to reply to Link-State Requests and to account new info - like forwarding OSPF routing updates

26
Q

purpose of Link-State Acknowledgement (LSAck) packet

A

used to acknowledge that the LSU has been received by the router
has empty data field

27
Q

what field in a Hello Packet is used in DR and BDR election?

what numbers are used?

A

Router Priority
0-255
1 default
higher the number = more likely to come the DR on the link

28
Q

list the states OSPF progresses through while attempting to reach convergence

A
  • Down State
  • Init State
  • Two-Way State
  • ExStart State
  • Exchange State
  • Loading State
  • Full State
29
Q

while OSPF is attempting to reach convergence, in what state is DR/BDR elected?

A

Two-Way State

30
Q

while OSPF is attempting to reach convergence, in what state does the router send Hello packets

A

Down State

31
Q

which three OSPF states are involved when two routers are forming an adjacency

A

Down State, Init State and Two-Way State

32
Q

while OSPF is attempting to reach convergence, in what state do the routers decide which router will initiate the DBD packet exchange and decide upon the initial DBD packet sequence number

A

ExStart State

33
Q

while OSPF is attempting to reach convergence, in what state are LSRs and LSUs used to gain additional route info? And routes are processed using the SPF algorithm

A

Loading State

34
Q

while OSPF is attempting to reach convergence, in what state is communication btwn two routers bidirectional?

A

Two-Way State

35
Q

what IP is Hello Packet sent on

A

224.0.0.5

All OSPF Routers IPv4 Multicase Address

36
Q

when are LSUs sent to neighbors

A

when network topology change is detected or every 30 mins

37
Q

what is the point of electing a DR

A

OSPF elects a DR to be the collection and distribution point for LSAs sent and received.

Cisco CCNA 3/3: Enterprise Networking, Security, and Automation v7 (9 decks)

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