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Routers and SwitchesRouters and Switches

byby

Steve MackaySteve Mackay

fromfrom

Engineering Institute ofEngineering Institute ofTechnologyTechnology

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Topics

Attend this complimentary session andgain an understanding on how routers andswitches operate based on the TCP/IP

suite of protocols.

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EIT Micro-Course Series• Every two weeks we present a 35

to 45 minute interactive course

• Practical, useful with Q & Athroughout

• PID loop Tuning / Arc FlashProtection, Functional Safety,Troubleshooting conveyorspresented so far

• Upcoming: – Electrical Troubleshooting and

much much more…..

• Go to http://www.eit.edu.au/free-courses

• You get the recording and slides

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Topics

• Detail how TCP/IPprotocol works

• How a router andswitch operate

• Examine RoutingBasics

• SimpleTroubleshooting Tips

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Why Bother ?Useful to understandhow routers work sothat you can moreeffectively design andtroubleshoot yourTCP/IP networks.

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1.0 How TCP/IP Works

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The OSI ModelOSI LAYER PROTOCOL IMPLEMENTATION ARPA LAYER

APP LI CATI ON Fi le Tr an sf ere E le ct ron ic Ma ilTerminal

EmulationFile Transfer Client/Server

Network

Management

PRESENTATIONFile Transfer

Protocol (FTP)

Simple Mail

Transfer

Protocol (SMTP)

TELNET

Protocol

Trivial File

Transfere

Protocol (TFTP)

Sun

Microsystems.

Network file

Systems

Protocol NFS

Simple Network

Management

Protocol

(SNMP)

PROCESS ANDAPPLICATION

SESSION MIL-STD 1780

RFC 959 

MIL-STD 1781

RFC 821

MIL-STD 1782

RFC854 RFC 783 

RFC's 1014,

1057 & 1094 RFC 1157 

TRANSPORTTransmission Control Protocol (TCP)

MIL-STD 1778 RFC 793

User Datagram Protocol (UDP) RFC

768

HOST

TO

HOST

NETWORKAddress Resolution ARP

RFC 826 & RARP RFC 903

Internet Protocol (IP)

MIL STD 1777 & RFC 791

Internet Control Message

Protocol (ICMP) RFC 792INTERNET

DATA LINKNetwork Interface Cards: Ethernet, Token-Ring, ARCNET, MAN and WAN. RFC 894, 1042, 1201 and

othersNETWORK

P HY SI CAL T ra ns mi ss ion Med ia : Twis te d p ai r ca bl e, Co ax ia l Cabl e, Fi be r Opti cs , Wir le ss Medi a etc . e tc . I NT ERFACE

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IP Protocol

• Primarily for routing

• Version 4 uses 32-bit address

• Version 6 uses 128-bit address

• IP is hierarchical vs MAC which is flat andunique for each node

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IP address Notation – The IP address consists of 32 bits, e.g.

11000000011001000110010000000001.

 – Four octets, which for ease of reference couldbe called a,b,c,d or w,x,y,z. We then converteach octet to decimal and write it thus:

• w x y z

• 11000000.01100100.01100100.00000001

• or• 192.100.100.1

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NetId and HostId

• Two portions to IP address

• Network ID (NetID)

• Host ID (HostID)

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Transmission Control Protocol• Connection oriented

• Reliable

• Establishes a session before data istransmitted

• Significant overhead in processing andheader

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TCP functions

• Fragmentation

• Data stream reconstruction

• Receipt acknowledgement

• Socket services for multiple connections

• Packet verification and error control

• Flow Control

• Packet sequencing and reordering

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Ports and Sockets• TCP needs to know which process on a

particular machine the packet is destinedfor.

• Done by port assignments

• Specific port numbers are assigned by theIANA

• Well know ports

• IP address + Port number = socket• Thus three addresses are used:

(MAC/IP/Port#)

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    !"#

  $% &' $# () )'

    $& '

  $*+ $,' $() +)#-

  .+ $ ' / 0 1, $#

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TCP Header Format

$ 2 / . 3 3 / $ $

3 / $ & . + & .2 + . 3 3 / $ $

4 / 2 & 5   & 5 / + & %

2 0 ) %

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User Datagram Protocol

! "#$% "& !'

 

 

())

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APPLICATION LAYERPROTOCOLS

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2.0 How a

Router and Switch

Operate

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Fundamentals• Routers are used to interconnect multiple

networks.

• Connected over wide geographical areaswith WAN’s

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• Act of movinginformation acrossan Internet workfrom a source to adestinationRouting

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Routing metrics

• Path length

• Reliability

• Delay

• Bandwidth

• Load

• Communicationcost

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Components of Router

• CPU and RAM

• BIOS

• Operating System (eg Cisco’s

Internetwork Operating system)• Motherboard

• I/O Ports

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Two methods of Operation• Static routing

• Dynamic Routing

 – Distance Vector

 – Link-state

 – Hybrids

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Static Routing

• Fixed static routes configured by networkadministrator.

• Optimum routes are programmed in.

• Good for security as ingress into yurnetwork can be controlled.

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Three methods of dynamic routing• Distance vector

• Link-state

• Hybrids

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Distance-vector routing

• Periodically pass copies of their tables toimmediate network neighbours.

• Each recipient adds a distance vector to

its table.

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Advantages of distance-vector• Simple to configure/maintain and use.

• RIP uses only distance to work out bestroute.

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Drawbacks to Distance-vector

• Some time to converge on newunderstanding of network.

• Bandwidth and traffic levels can affect

performance of network.

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Link-state routing• Shortest path first protocols

• Exchange of link-state advertisements(LSA) to other routers.

• LSA’s are triggered by an event ratherthan running periodically.

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Disadvantages of Link State

• Flood the network during initial discoveryprocess

• Memory and processor intensive

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Advantages• Gracefully weather effects of topology

changes

• Lower overheads as no time-drivenupdates

• Better scalability for networks

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Hybridized Routing

• Use distance vector metrics

• More accurate than conventional distance-vector protocols

• Converge more rapidly than distance-vector but avoid overheads of link-stateupdates.

• Best example is EIGRP.

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Convergence• Whenever a change occurs in a network’s

topology, all routers must develop a newunderstanding of new topology.

• Routers take time to converge to the newconsensus of what the topology is.

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3.0 Routing Protocols

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Routing Protocols• RIP and

• RIP 2

• IGRP

• OSPF

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Routing Information Protocol

• One of the oldest routing protocols.

• RIP uses a special packet to collect andshare information about distances.

• RIP is a routing protocol; not a routed protocol (e.g. TCP/IP).

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Operation of RIP• Routers periodically pass copies of their

routing tables to immediate neighbours.

• Each recipient adds a distance vector tothe table and forwards the table to itsimmediate neighbours.

• RIP uses as a metric the hop count.

• RIP only records one route per destination(even if there are more).

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Limitations of RIP (RoutingInformation Protocol)

• Hop count restriction

• Least hop path

• High routing overhead

• Routing flexibility is not allowed

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RIP Packet format

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RIP packet fields

• Command

• Version number

• Zero

• Address-Family Identifier (AFI)

• Address

• Metric

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Routing table

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Routing table

Routing table provides:

• Ultimate destination

• Next hop on the way to that destination

• A metric

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Routing database

• IP Address

• Gateway

• Distance

• Route change flag

• Timers

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RIP algorithm

• Update

• Propagation

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RIP-2

• Authentication

• Subnet Masks

• Next Hop IP Addresses

• Multicasting RIP-2 messages

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IP RIP 2 packet

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IP RIP 2 packet format fields

• Command

• Version

• Address-Family Identifier (AFI)

• Route tag• IP address

• Subnet mask

• Next hop

• Metric

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Limitations of RIP-2• 15-hop maximum

• Counting to infinity (e.g. routing loop)

• Static distance vector metrics

• Lack of alternative routes (single routes)

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Goals of IGRP• Stable routing

• Fast response to changes

• Low overhead

• Splitting traffic

• Account error rates

• Handle multiple types of service

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Metrics

• Hop count

• Packet size (Maximum Transmission Unit -MTU)

• Link’s bandwidth• Delay

• Loading

• Reliability

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Formula - Metric• Metric = K * Bandwidth + (K2 *

Bandwidth)/(256 - Load) + K3 * Delay

• K1,K2 and K3 are weighting factors

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Reliability added in...

• Metric = Metric * [K5/(reliability +K4)

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Limitations of IGRP

• Does not include subnet maskinformation

• Does not support the use of VLSM

• Sends updates to the broadcastaddress

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Open Shortest Path First (OSPF)

• Link State Routing Protocol

• Distance vector know nothing abouttopology of network

• OSPF assign a “path cost” to routes• Divide reference bandwidth by circuits

preconfigured bandwidth

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Example of calculation• Cisco uses reference bandwith of

100MBps

• 100 MBps circuit has an OSPF cost of100/100 = 1

• A 1.544Mbps circuit has an OSPF cost of100/1.544 = 65

• OSPF routers pick the lowest cost path(i.e. highest speed)

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4. Simple Troubleshooting Tips

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Network Troubleshooting

• Knowledge of networking protocols

• Understanding of networks’ topology andlayout

• Troubleshooting tools

• Some luck ? Preferably not.

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Network Troubleshooting(cont.)

• Utilisation on the Ethernet network

• Low utilisation but high errors

• High number of packets but low datatransfer

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TCP/IP Utility Programs forTroubleshooting

• netstat

• ping

• traceroute

• arp• ripquery

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Example of the use of a few ofthe TCP/IP utilities together

• ping• netstat-nr

• Tracert (or traceroute)

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Unreliable Connections

• ping

• tracert (or traceroute)

• netstat

• ping-f

• netstat

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Network Congestion

• ping• tracert(or traceroute)

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THANK YOU FOR ATTENDING

If you are interested in further training please visit;

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