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IP Engineering > Week 9: Link State Protocol (LSP) > Flashcards

Week 9: Link State Protocol (LSP) Flashcards

1
Q

What is a Link-State Routing Protocol?

A

A Distributed DB Algorithm

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2
Q

What occurs in a Link-State Routing Protocols?

A
  1. Each router is responsible for meeting its neighbours & learning who they are
  2. Each router constrcuts an LSA which contains a list of the neighbours (links) & costs to them
  3. The LSA is sent to all routers in the AS & each router stores the most recent LSA from all other routers (LSA-db)
  4. Each router now computes best routes to all networks based on the LSA information
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3
Q

What is an LSA?

A

Link State Advertisement

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4
Q

What are the properties of Distance Vector Routing Protocols?

A
  • Entire Routing Table is sent as an Update
  • Periodically sends updates every 30 or 90 seconds
  • Updates are Broadcast or Multicast
  • Updates are sent to directly connected neighbour only
  • Router don’t have end to end visibility of entire network
  • Prone to routing loops
  • Slow to converge
  • Easy to configure & administer
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5
Q

What are the properties of Link-State routing protocols?

A
  • Updates are incremental, & entire routing table is not sent as update
  • Updates are triggered, not periodic
  • Updates are Multicast
  • Updates are sent to entire network
  • Updates carry SPF tree information & cost calculation for entire topology
  • No routing loops
  • convergence is fast b/c of triggered updates
  • Harder to configure
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6
Q

Give an example of a Distance Vector Routing Protocol

A

RIP

IGRP

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7
Q

Give an example of Link State routing Protocols

A

OSPF

IS-IS

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8
Q

OPSF is what type of Routing Protocol?

A

Link-State

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9
Q

What do Link-State protocols allow?

A

Allow Routers to share a common view of the entire network

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10
Q

In OSPF, what is sent out by routers?

A

LSA’s describing their attached links to all routers in an area

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11
Q

In OPSF, each router holds what?

A

A Topological Database of the entire area

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12
Q

What routing algorithm is used by OSPF?

A

Shortest Path First (SPF) a.k.a. Dijkstra

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13
Q

True or False: SPF is a routing protocol

A

False, SPF is the algorithm used by the routing protocol

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14
Q

What are the reasons to implement OSPF in a Hierarchical Design?

A
  • Decrease routing overhead
  • Speed up convergence
  • Confine network instability to single areas of the network
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15
Q

What is a Router ID?

A

An IP address used to identify the router

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16
Q

What is a Neighbour?

A

Two or more routers having an interface on common network

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17
Q

What is Adjacency?

A

Permits direct exchange of route updates

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18
Q

What is a Designated Route?

A

elected to minimize adjacencies

19
Q

What is a Backup Designated Router?

A

A standby for a Designated Router

20
Q

What is a Hello Protocol?

A

Provides dynamic neighbour discovery

21
Q

What is a Neighbour Database?

A

A list of all OSPF routers for which Hello Packets have been seen

22
Q

What is a Topological Database?

A

Information from all of the LSA’s received for an area

23
Q

What is a Link State Advertisement (LSA)?

A

A packet containing link-state & routing information that’s shared among OSPF Routers

24
Q

What is an OSPF Area?

A

A group of networks & routers sharing a common area ID

25
Q

What are the steps in OSPF Operation?

A
  1. Neighbour & Adjacency Initialization
  2. LSA Flooding
  3. Shortest Path First Tree Calculation
26
Q

In OSPF operation, what happens during Neighbour & Adjacency initialization?

A
  • An OSPF Router forms adjacencies with neighbours

- A Designated Router and Backup Designated Router are elected in OSPF

27
Q

In OSPF operation, what happens during LSA flooding?

A

routers flood their Link State Advertisements

28
Q

What is the general format of a Hello Message?

A
  • Hello Layer
  • OSPF Layer
  • IP Packet Layer
  • Layer 2 Info Layer
29
Q

In a Hello Message, what is the Hello segment?

A
  • The Presentation Card

- Contains Router ID & Timers

30
Q

In a Hello Message, what is the OSPF Layer?

A

The general header for OSPF

31
Q

In a Hello Message, what is the IP Packet Layer?

A

Encapsulation of the OSPF Message

32
Q

In a Hello Message, what is the Layer 2 Information layer?

A

Contains a protocol such as Ethernet to deliver the packet to the next hop

33
Q

What is LSA Flooding?

A

Link-State data is shared with all OSPF routers within an area via LSA updates (LSU)

34
Q

What is the reserved multicast address for OSPF?

A

224.0.0.5

35
Q

True or False: Each recipient doesn’t have to acknowledge that an LSA flood update has been recieved

A

False, Each recipient must acknowledge that the flooded update has been received

36
Q

What metric does OSPF use?

A

Cost

37
Q

What is the cost metric for OSPF associated with?

A

every outgoing interface included in an SPF Tree

38
Q

What are the five different types of OSPF Packets?

A
  1. Hello Packet
  2. Database Description Packet
  3. Link State Request Packet
  4. Link State Update Packet
  5. Link State Acknowledgement
39
Q

What is the function of the Hello Packet in OSPF?

A

Neighbour discovery & adjacency maintenance

40
Q

What is the function of the Database Description Packet in OSPF?

A

Summarizes topological database b/w routers during initialization of neighbour relationship

41
Q

What is the function of the Link State Request Packet in OSPF?

A

Request Link State information from a neighbour’s database

42
Q

What is the function of the Link State Update Packet in OSPF?

A

Advertises available links via network flooding

43
Q

What is the function of the Link State Acknowledgement Packet in OSPF?

A

Response to flooded links sent via Link State Updates

IP Engineering (15 decks)

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