Week 9: Link State Protocol (LSP) Flashcards by Mark Philips

What is a Link-State Routing Protocol?

A Distributed DB Algorithm

How well did you know this?

Not at all

Perfectly

What occurs in a Link-State Routing Protocols?

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

How well did you know this?

Not at all

Perfectly

What is an LSA?

Link State Advertisement

How well did you know this?

Not at all

Perfectly

What are the properties of Distance Vector Routing Protocols?

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

How well did you know this?

Not at all

Perfectly

What are the properties of Link-State routing protocols?

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

How well did you know this?

Not at all

Perfectly

Give an example of a Distance Vector Routing Protocol

RIP

IGRP

How well did you know this?

Not at all

Perfectly

Give an example of Link State routing Protocols

OSPF

IS-IS

How well did you know this?

Not at all

Perfectly

OPSF is what type of Routing Protocol?

Link-State

How well did you know this?

Not at all

Perfectly

What do Link-State protocols allow?

Allow Routers to share a common view of the entire network

How well did you know this?

Not at all

Perfectly

In OSPF, what is sent out by routers?

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

How well did you know this?

Not at all

Perfectly

In OPSF, each router holds what?

A Topological Database of the entire area

How well did you know this?

Not at all

Perfectly

What routing algorithm is used by OSPF?

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

How well did you know this?

Not at all

Perfectly

True or False: SPF is a routing protocol

False, SPF is the algorithm used by the routing protocol

How well did you know this?

Not at all

Perfectly

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

Decrease routing overhead
Speed up convergence
Confine network instability to single areas of the network

How well did you know this?

Not at all

Perfectly

What is a Router ID?

An IP address used to identify the router

How well did you know this?

Not at all

Perfectly

What is a Neighbour?

Two or more routers having an interface on common network

How well did you know this?

Not at all

Perfectly

What is Adjacency?

Permits direct exchange of route updates

How well did you know this?

Not at all

Perfectly

What is a Designated Route?

elected to minimize adjacencies

What is a Backup Designated Router?

A standby for a Designated Router

What is a Hello Protocol?

Provides dynamic neighbour discovery

What is a Neighbour Database?

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

What is a Topological Database?

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

What is a Link State Advertisement (LSA)?

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

What is an OSPF Area?

A group of networks & routers sharing a common area ID

What are the steps in OSPF Operation?

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

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

- An OSPF Router forms adjacencies with neighbours | - A Designated Router and Backup Designated Router are elected in OSPF

In OSPF operation, what happens during LSA flooding?

routers flood their Link State Advertisements

What is the general format of a Hello Message?

- Hello Layer - OSPF Layer - IP Packet Layer - Layer 2 Info Layer

In a Hello Message, what is the Hello segment?

- The Presentation Card | - Contains Router ID & Timers

In a Hello Message, what is the OSPF Layer?

The general header for OSPF

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

Encapsulation of the OSPF Message

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

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

What is LSA Flooding?

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

What is the reserved multicast address for OSPF?

224.0.0.5

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

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

What metric does OSPF use?

Cost

What is the cost metric for OSPF associated with?

every outgoing interface included in an SPF Tree

What are the five different types of OSPF Packets?

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

What is the function of the Hello Packet in OSPF?

Neighbour discovery & adjacency maintenance

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

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

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

Request Link State information from a neighbour's database

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

Advertises available links via network flooding

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

Response to flooded links sent via Link State Updates