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Cisco CCNA 2 > 7a - OSPF Concepts > Flashcards

7a - OSPF Concepts Flashcards

1
Q

What are the 3 methods routers add routes to their routing tables?

A
  • Connected routes * Static Routes * Routes learned from a routing protocol
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2
Q

What is a ROUTING PROTOCOL?

A

A set of messages, rules, and algorithms used by routers for the overall purpose of learning routes. This process includes the exchange and analysis of routing information. Each router chooses the best route to each subnet (path selection) and finally places those best routes in its IP routing table. Examples include RIP, EIGRP, OSPF, and BGP.

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3
Q

What is a ROUTED PROTOCOL?

A

A Protocol that can be routed using a routing protocol. Examples of Routed Protocols include IP Version 4 (IPv4) and IP Version 6 (IPv6).

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4
Q

What is Path Selection?

A

Part of the job of a routing protocol, in which the routing protocol chooses the best route.

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5
Q

What are the general functions of a routing protocol?

A
  1. LEARN routing information about IP subnets from neighboring routers.
  2. ADVERTISE routing information about IP subnets to neighboring routers.
  3. PICK THE BEST ROUTE based on a metric if more than one possible route exists to reach one subnet, .
  4. REACT if the topology changes picking a new best route.
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6
Q

What is convergence?

A

When routers realize something has changed, they advertise the information about the changes to all the other routers, and all the routers then choose the currently best routes for each subnet.

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7
Q

What is an IGP?

A

Interior Gateway Protocol - A routing protocol that was designed and intended for use inside a single autonomous system (AS)

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8
Q

What is an EGP?

A

Exterior Gateway Protocol - A routing protocol that was designed and intended for use BETWEEN different autonomous systems. Today BGP is the only one.

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9
Q

What is an AS?

A

Autonomous System - An AS is a network under the administrative control of a single organization.

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10
Q

What does ASN stand for?

A

Autonomous System Number - typically assigned by IANA.

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11
Q

What are the three Routing Protocol Algorithms?

A
  • Distance Vector
  • Adanced Distance Vector or Balanced Hybrid
  • Link State
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12
Q

What metric does RIPv2 use?

A

Hop count

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13
Q

What metric does OSPF use?

A

Cost

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14
Q

What metric does EIGRP use?

A

bandwidth and delay

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15
Q

What is Administrative Distance?

A

Administrative distance is a number that denotes how believable an entire routing protocol is on a single router.

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16
Q

What is an LSA

A

Link State Advertisement. A data structure by which OSPF routers exchange data about the network.

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17
Q

What is an LSDB

A

LSA Database. A database collection of all the LSAs known to the router.

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18
Q

What show command lists information about the LSDB

A

show ip ospf database

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19
Q

What is the default LSA aging timer?

A

30 minutes

20
Q

What is SPF?

A

Dijkstra’s Shortest Path First algorithm run by OSPF on the LSDB. The algorithm builds the routes that the local router should add to its routing table.

21
Q

What show command displays information about an OSPF neighbor?

A

show ip ospf neighbors

22
Q

What is Distance Vector?

A

Sometimes called Bellman Ford, It is sufficient for each router to advertise just a list (a vector) of known networks and its own distance to each of them.

23
Q

Once the SPF algorithm has run what is the output?

A

Routes list:

  • subnet number
  • mask
  • outgoing interface
  • next hop router IP address.
24
Q

All link state routing protocols use an algorithm to process the LSDB. What is the name of the algorithm?

A

Dijkstra’s SPF

25
What types of messages does OSPF send to become neighbors with another router?
OSPF multicast Hello Messages
26
If a neighbor relationship fails what is the reaction by an OSPF router?
* It re-floods LSAs that previously relied on the link to the failed neighbor * re-calculates SFP to calculate new routes.
27
What protocol and port does an OSPF Hello message use?
IP 89
28
What multicast address is used by Hello messages?
224.0.0.5
29
What states do 2 router go through when becoming neighbors?
* Init * 2-way * ex-start * Exchange * Loading * Full
30
What are the packets called that are used to send LSAs?
LSUs (Link State Updates)
31
What is the packet called that is sent with just a summary list of what is in the LSDB to allow another router to determine which LSAs it already has and which ones it needs?
Database Descriptor Packet (DD packet)
32
Once a router knows which LSAs it needs from its neighbor what kind of packet is sent asking for the specific LSAs?
Link-state Request Packet
33
What happens at the Init State?
The routers are in the process of becoming neighbors.
34
What happens at the 2-Way State
After the Init state the routers exchange Hellos once more and enter the 2-way state. At this point they meet all the requirements necessary to become neighbors and are ready to exchange LSDB information.
35
What happens at the Ex-start State?
Database Descriptors are exchanged. The routers determine which LSAs they have and which ones they need.
36
What happens during the Loading State?
Link-state Request packets are exchanged letting each other know which LSAs it needs. Then LSUs are exchanged containing multiple LSAs each.
37
What happens at the Full State?
The routers have fully exchanged the contents of the LSDB's.
38
How do neighbors check to make sure each other is still up?
They exchange Hellos once every Hello Interval. If the neighbor doesn't respond back within the Dead Interval it means the neighbor has failed.
39
What is the default Hello Interval?
10 seconds
40
What is the default Dead Interval?
4 times the Hello interval.
41
How often are LSAs re-flooded even if no changes have occurred?
Once every 30 minutes from the time the individual LSA was created (to prevent a big flood event)
42
What is the difference between Adjacent routers and Fully Adjacent routers?
On an Ethernet network with DR and BDR, the DROthers become Fully Adjacent with the DR and BDR but only Adjacent with each other.
43
What is the OSPF Metric based on?
The sum of the costs for each outgoing interface on the way to the network.
44
What are the downsides to just having one big area 0?
* Larger topology would require more memory on each router * Larger topology would require more CPU every time SPF was run. * A single interface change would require every router in the area to re-run SPF.
45
What is an Inter-area route?
A route to a network in a Different area.
46
What is an Intra-area route?
A route to a network in the SAME area.

Cisco CCNA 2 (40 decks)

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