Routing Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked...

Routing

Networks and Protocols

Prepared by: TGK First Prepared on: Last Modified on:

Quality checked by: Copyright 2009 Asia Pacific Institute of Information Technology


Routing

Slide 2 of 27

Topic & Structure of the lesson

Routing CharacteristicsRouting StrategiesRouting Algorithms


Routing

Slide 3 of 27

Learning Outcomes

At the end of this module, YOU should be able to:

• Discuss the characteristics required in performing routing functions

• Discuss the routing strategies used to determine appropriate communication path

• Discuss the operations of Link State and Distance Vector routing algorithms


Routing

Slide 4 of 27

Key Terms you must be able to use

If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams:

• Routing characteristics• Routing strategies• Routing algorithms


Routing

Slide 5 of 27

Main Teaching Points

• Route selection• Minimum hop• Fixed• Flood• Random• Adaptive• Link State• Distance Vector• Dijkstra’s• Bellman-Ford• Link State Advertisements


Routing

Slide 6 of 27

Routing Characteristics

• Complex, crucial aspect of packet switched networks

• Characteristics required

• Correctness and simplicity

• Robustness and stability

• Fairness and optimality

• Efficiency

• Used for selection of route

• Minimum hop

• Least cost


Routing

Slide 7 of 27

Routing Characteristics


Routing

Slide 8 of 27

Routing Strategies

• Fixed• Flooding• Random• Adaptive• Fixed:

• Single permanent route for each source to destination pair

• Determine routes using a least cost algorithm• Route fixed, at least until a change in network

topology• Flooding RoutingFlooding Routing

• No network info required• Packet sent by node to every neighbor


Routing

Slide 9 of 27

• Incoming packets retransmitted on every link except incoming link

• Eventually a number of copies will arrive at destination

• Each packet is uniquely numbered so duplicates can be discarded

• Nodes can remember packets already forwarded to keep network load in bounds

• Can include a hop count in packets

Routing Strategies


Routing

Slide 10 of 27

Figure 10.8 Flooding Example(hop count = 3) William Stalling –D&C Communication

Routing Strategies


Routing

Slide 11 of 27

Routing Strategies

• Properties of Flooding Routing• All possible routes are tried• Very robust• At least one packet will have taken minimum hop

count route• Can be used to set up virtual circuit• All nodes are visited• Useful to distribute information (e.g. routing)

• Random RoutingRandom Routing• Node selects one outgoing path for retransmission of

incoming packet• Selection can be random or round robin• Can select outgoing path based on probability

calculation


Routing

• No network information needed• Route is typically not least cost nor minimum hop

• Adaptive RoutingAdaptive Routing• Used by almost all packet switching networks• Routing decisions change as conditions on the

network change (failure, congestion, etc.)• Requires information about network• Decisions more complex• Tradeoff between quality of network info and

overhead• Adaptive Routing ClassificationAdaptive Routing Classification

• Based on information sources• Local (isolated)

• Route to outgoing link with shortest queue• Can include bias for each destination

Routing Strategies


Routing

Slide 13 of 27

• Rarely used - do not make use of easily available info

• Adjacent nodes• All nodes

Routing Strategies


Routing

Slide 14 of 27

Routing Algorithms

• Distance Vector

• Also known as Bellman-Ford algorithm

• Passes periodic copies of a routing table

• Regular updates between routers communicate

topology changes

• Perform routing decisions based on the information

by neighboring routers

• Based on the distance (number of hops) and vector

(direction)

• Before sending an update, each router adds its own

distance value to the route's metric


Routing

• When a router receives an update, it maps the learned

network to the receiving interface

• The router then uses that interface to reach those

destinations

• Maintain a database of network topology information

• Send its entire routing table to each of its adjacent

neighbors

• Router does not know the exact topology of an

internetwork. Why?

• Update includes a list of subnets and the distances in

metric

Routing Algorithms


Routing

Slide 16 of 27

• Routers do not know the network topology except the

neighboring routers

• If there’s multiple routes, chooses the best route which has

the lowest metric

• Limitations

• Distance vector are classful routing protocols

• Do not send subnet information in updates

• Do not support scalability features such as Variable

Length Subnet Masking (VLSM) or super-netting

• Converge slowly compared to link-state protocols – not

suitable for complex and scalable internetworks

Routing Algorithms


Routing

Slide 17 of 27

Routing Algorithms

• Examples of Distance Vector Routing Protocol

• Routing Information Protocol (RIP)

• Interior Gateway Routing Protocol (IGRP)

• Enhanced IGRP (EIGRP) – balanced hybrid

• Border Gateway Protocol (BGP)


Routing

Slide 18 of 27

• Link State

• Uses Shortest Path First (SPF) algorithms/Dijkstra

Algorithms

• Flood routing information to all routers in the internetwork

that creates a map of the entire network

• Assemble all the information to calculate the shortest path

routes and builds routing tables showing the best path

• Once converged, send update packets, which contain only

changes rather than whole routing table

• Update packets are passed across the network in event-

triggered updates

Routing Algorithms


Routing

Slide 19 of 27

Routing Algorithms

• Builds a complete database of all the link states

• Router gathers enough information to create the

network map

• Each router individually runs the SPF algorithm on its

link-state database

• to identify the best paths

• These paths form a tree with the local router as its

root

• Advertise the states of their links to all other routers

in the area


Routing

• When a network link changes state, a notification

called a link-state advertisement (LSA) is flooded

throughout the network

• All the routers note the change and adjust their routes

accordingly

• Also has periodic re-flooding of LSA but longer

interval time

• More reliable, easier to debug, and less bandwidth-

intensive

• Link-state advertisements (LSAs) – routing

information that is sent between routers

Routing Algorithms


Routing

• Link-state advertisements (LSAs) – routing information that

is sent between routers

– Router LSA – identifies router ID, router interfaces IP

addresses, status (up or down) of each interface, cost

(metric) associated with each interface

– Link LSA – identifies each subnet and routers that are

attached to that subnet

Topological database – collection of information (data

structure) gathered from LSAs

SPF algorithm – calculation performed on the database

resulting in the SPF tree

Routing Algorithms


Routing Routing tables – A list of the known paths and interfaces

Advantages

Faster Convergence

Improved bandwidth utilization

Support Classless Inter-Domain Routing (CIDR), VLSM,

and super-netting

Limitations

Processor overhead

Memory requirements

Bandwidth Consumption

Complex administration

Routing Algorithms


Routing

Slide 23 of 27

Quick Review Question


Routing

Slide 24 of 27

Follow Up Assignment


Routing

Slide 25 of 27

Summary of Main Teaching Points


Routing

Slide 26 of 27

Q & A

Question and Answer Session


Routing

Slide 27 of 27

Topic and Structure of next session

• Networking and Internetworking Devices

Repeaters Bridges Routers Gateways

Next Session

Routing Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked...

Documents

Transcript of Routing Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked...