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Advanced Networking > 5 - Link State Routing > Flashcards

5 - Link State Routing Flashcards

1
Q

What do link state protocols atempt to achieve?

A

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

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2
Q

What do routers broadcast the state of?

A

The state of its locally attached links and IP subnets

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3
Q

What do routers construct?

in terms of toplogy

A

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

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4
Q

Topology Database

A

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

List of shortest paths to destinations

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5
Q

How are removals announced?

Link State Operation

A

By metric set to infinity

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6
Q

What process occurs when adjacencies refresh?

A

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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7
Q

What type of algorithm is Djikstra’s Algorithm?

A

Shortest Path First graph algorithm

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8
Q

Summary of Djikstra’s Algo

A

Search outward and add router IDs as you expand the front

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9
Q

OSPF

A

Open Shortest Path First

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10
Q

OSPF two level hierarchy

2 items

A

Local area and backbone

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11
Q

OSPF: Link state announcements only where?

A

Link state announcements only in respective areas

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12
Q

OSPF: What knowledge do nodes in each area have?

A

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

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13
Q

Area border routers

A

Summarise distances to networks in the area and advertise them.

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14
Q

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

A

Run an OSPF routing algorithm limited to the backbone

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15
Q

Boundary routers

A

Connect to other ASes

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16
Q

IS:IS Routing Protocol

A

Intermediate System to Intermediate System Routing

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17
Q

Intermediate System

A

Router

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18
Q

End System

A

Network host or workstation

19
Q

Network Service Access Point

A

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

NSAP address is location

20
Q

Subnetwork point of attachment

A

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

21
Q

What is Packet data unit (PDU) analogous to?

A

Analogous to IP Packet

22
Q

Link state PDU

A

Routing information packet

23
Q

Which L2 protocols form Connectionless Network Service?

A

CLNP
IS-IS
ES-IS

24
Q

ES-IS

A

End System to Intermediate System

25
Q

What does each router contain?

Database of entire … what?

A

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

26
Q

What type of communication occurs when link state changes occur?

A

They are flooded across the network

27
Q

What layers does ISIS operate over?

(Hint:2 different layers)

A

Layer 1 (backbone)
Layer 2 (Areas)

28
Q

Does ISIS have a backbone area (like OSPF)?

A

No

29
Q

What is the backbone on ISIS?

A

Contiguous collection of Level 2 capable routers

30
Q

Where do IS-IS area borders reside?

A

Links

31
Q

Network Entity Title

A

Identifies each router in ISIS

32
Q

CLNS

A

Connection-less mode Network Service

33
Q

NSAP

A

Network Service Access Point address

34
Q

CLNS Addressing: NSAP 3 main components

A

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

35
Q

CLNS Addressing cons

A
  • 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
36
Q

SPF

A

Shortest Path First

37
Q

By default, SPF runs no more frequently than…?

SPF = Shortest Path First

A

5 seconds

38
Q

When is a full SPF run?

A

When topology changes

39
Q

PRC

A

Partial Route Calculation

40
Q

When is PRC used?

A

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

41
Q

IS-IS Basic Config

Each router/interface needs…

A

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

42
Q

IS-IS Loopback Address

Is it unique? What is the subnet?

A

Unique for each router.

/32 subnet

43
Q

IS-IS NSAP address format

A

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

44
Q

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

A

49.0001.0070.0700.7001.00

Advanced Networking (11 decks)

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