5 - Link State Routing Flashcards by Josh Davidson

What do link state protocols atempt to achieve?

Minimise convergence times.
Eliminate non-transient packet looping
Allows multiple metrics to be used

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What do routers broadcast the state of?

The state of its locally attached links and IP subnets

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What do routers construct?

in terms of toplogy

A complete topology view of the net, based on link state updates.
Its next-hop routing table

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Topology Database

Router IDs
Link IDs
- From Router ID
- To Router ID
Metric(s)
Sequence Number

List of shortest paths to destinations

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How are removals announced?

Link State Operation

By metric set to infinity

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What process occurs when adjacencies refresh?

Neighbours use “hello” protocol
If a router loses a neighbour then recompute routes via there.
Send announcemens with metric set to infinity

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What type of algorithm is Djikstra’s Algorithm?

Shortest Path First graph algorithm

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Summary of Djikstra’s Algo

Search outward and add router IDs as you expand the front

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OSPF

Open Shortest Path First

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OSPF two level hierarchy

2 items

Local area and backbone

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OSPF: Link state announcements only where?

Link state announcements only in respective areas

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OSPF: What knowledge do nodes in each area have?

Nodes in each area have detailed topology and only know direction (shortest path) to networks in other other areas

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Area border routers

Summarise distances to networks in the area and advertise them.

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What algorithm do Backbone routers run and where is it limited to?

Run an OSPF routing algorithm limited to the backbone

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Boundary routers

Connect to other ASes

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IS:IS Routing Protocol

Intermediate System to Intermediate System Routing

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Intermediate System

Router

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End System

Network host or workstation

Network Service Access Point

logical point between network and transport layers where services are delivered to transport

NSAP address is location

Subnetwork point of attachment

Datalink interface (address used in IS-IS to reach neighbor on broadcast media)

What is Packet data unit (PDU) analogous to?

Analogous to IP Packet

Link state PDU

Routing information packet

Which L2 protocols form Connectionless Network Service?

CLNP
IS-IS
ES-IS

ES-IS

End System to Intermediate System

What does each router contain? | Database of entire ... what?

Database of entire topology - links + state (inc cost) The same information as ny other router The best path to every destination

What type of communication occurs when link state changes occur?

They are flooded across the network

What layers does ISIS operate over? | (Hint:2 different layers)

Layer 1 (backbone) Layer 2 (Areas)

Does ISIS have a backbone area (like OSPF)?

What is the backbone on ISIS?

Contiguous collection of Level 2 capable routers

Where do IS-IS area borders reside?

Links

Network Entity Title

Identifies each router in ISIS

CLNS

Connection-less mode Network Service

NSAP

Network Service Access Point address

CLNS Addressing: NSAP 3 main components

Area ID (1 byte AFI + 1-12bytes area address) System ID (6 bytes) N-Selector (1byte)

CLNS Addressing cons

- At least one NSAP per node - All routers in same area must share Area ID - Each node in area must have unique System ID - All level 2 routers in domain must have unique SYstem IDs relative to each other

SPF

Shortest Path First

By default, SPF runs no more frequently than...? | SPF = Shortest Path First

5 seconds

When is a full SPF run?

When topology changes

PRC

Partial Route Calculation

When is PRC used?

When leaf elements such as IP prefixes change. (SPF)

IS-IS Basic Config | Each router/interface needs...

Each router needs a routeable loopback address. Each router needs an ID (NET) Each interface needs IS-IS on.

IS-IS Loopback Address | Is it unique? What is the subnet?

Unique for each router. /32 subnet

IS-IS NSAP address format

Start with AFI 49 Then area ID 0001 System ID - ABC.DEF.GHI.JKL goes to - ABCD.EFGH.IJKL End with 00

A NSAP address has AFI 49, Area ID 0001 and system id 7.7.7.1. What is the address?

49.0001.0070.0700.7001.00