1. Chapter 6 Switching and Routing
Computer Networking From LANs to WANs: Hardware, Software, and Security
Chapter 6
Switching and Routing
Cengage Learning: Computer Networking from LANs to WANs

2. Cengage Learning: Computer Networking from LANs to WANs
Objectives
Explain the basic differences between hubs and switches
Describe switching techniques and the function of the Spanning Tree Protocol
Describe the differences between a switch and a router
Explain the differences between distance-vector and link- state routing protocols and give examples of each
Describe how Classless Domain Internet Routing increased the availability of Internet addresses
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3. Cengage Learning: Computer Networking from LANs to WANs
Hubs versus Switches
Essential difference:
Hubs broadcast received frames to all other ports
Switches forward received frames to a specific port
Fully switched network
LAN stations connect to switched port
Partitions network into separate collision domains
Stations have unrestricted access to dedicated bandwidth, operate at switched port speed
Maximum Ethernet network size: 1024 nodes
Switches learn associated port MAC addresses
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4. Cengage Learning: Computer Networking from LANs to WANs
Station A transmit to F.
Hub broadcast to all
Wasted bandwidth
All six stations operate in same collision domain
There will compete for the available bandwidth
Figure 6-1 Comparing a hub and a switch
Station A transmit to F.
Switch sent directly to F on port 4.
Others will not received it
Network traffic is reduced
This network is call totally or fully switched network.
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5. Cengage Learning: Computer Networking from LANs to WANs
Hubs versus Switches
Switches learn associated port MAC addresses  capable of selective forwarding
Forward frame only to the port where the destination node is connected.
To perform selective forwarding, the switch maintains a table called the MAC table (also called the switch table or the bridge table).
The table keeps a list of MAC addresses together with the switch port number that leads to the device with that MAC address.
When a frame arrives from a certain port, the switch will check whether the source MAC address is already available in the table.
If not, then the source MAC address and its corresponding incoming port number will be recorded in the table.
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6. Cengage Learning: Computer Networking from LANs to WANs
Hubs versus Switches
When a frame comes, the switch will:
Read the destination MAC address in the header.
Find a matching address in the MAC table.
Address IN the MAC table
Forward the frame to the appropriate outgoing port as specified in the MAC table
Address NOT in the MAC table
the frame will be forwarded to all outgoing ports.
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7. Cengage Learning: Computer Networking from LANs to WANs
Switching Techniques
Store-and-Forward Switching
Entire frame is stored as it is received
No immediate routing decisions made
Latency
Cut-Through Switching
Forwarding process begins immediately
When incoming frame destination MAC address received
Advantage: Fixed latency
Disadvantage: Error propagation
No way to know either a frame being forwarded is good until it has been completely received.
Cengage Learning: Computer Networking from LANs to WANs

8. Spanning Tree Protocol
Spanning trees are designed to prevent loops in a bridged (switched) LAN.
Spanning Tree Algorithm is implemented by a compatible switch using the Spanning Tree Protocol (STP)
Prevents looping
Prevents network flooding from duplicate data frames
Dynamic filtering
Redundant links causing loops held in reserve in case the path to node become unavailable.
Cengage Learning: Computer Networking from LANs to WANs

9. Spanning Tree Protocol
The STP was replaced by Rapid Spanning Tree Algorithm and Protocol (RSTP)
Multiple Spanning Tree Protocol (MSTP)
Supports multiple trees in the network
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10. Cengage Learning: Computer Networking from LANs to WANs
Switches vs Routers
Switches: Layer 2 (Data-Link) devices
Use MAC addresses to forward frames
Used within networks to forward local traffic
Routers: Layer 3 hardware device
More complex than a switch
Microprocessor-based circuitry
Higher latency than a switch
Additional packet processing required
Routers used between networks
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11. Cengage Learning: Computer Networking from LANs to WANs
Switches vs Routers
Routers provide the following services:
Route discovery
Selection of the best route to a particular destination
Adaptation to changes in the network
Translation from one technology to another, such as Ethernet to Token Ring
Packet filtering based on IP address, protocol, or UDP / TCP port number
Connection to a WAN.
Non-routable protocols pass through a switch not a router
NetBEIU and ARP
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12. Cengage Learning: Computer Networking from LANs to WANs
Routing Protocol
Simple word - map-reading or direction-finding
Computer world - forwarding the information from some network node to another over an internetwork such as from a starting point (source) to its ending point (destination).
Perform different type of packet forwarding
Operate at Network layer (Layer 3)
Logical network formed by routers
Example: the Internet
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13. Cengage Learning: Computer Networking from LANs to WANs
Routing Protocol
Using a router, message are passed from one device to another until the message reaches the destination.
Can be different network types, different types of packet forwarding
Any traffic exchanged between any nodes on the local network can be delivered directly without the need for a router.
All traffic for a remote network must be passed on to the router.
Internet
PC1
PC2
PC3 R
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14. Cengage Learning: Computer Networking from LANs to WANs
Routing Protocol
Windows NETSTAT program
Shows currently active routes
To deliver a message to a remote network it must transmitted from the source to local router, (default gateway)
Then the data will be passed on to another router or to the host on the destination LAN.
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15. Cengage Learning: Computer Networking from LANs to WANs
Routing Protocol
Each router implements the routing process by forwarding messages towards their final destination using information stored in a routing table.
The routing table contains an entry that indicates the best path to send the data to the destination.
Cengage Learning: Computer Networking from LANs to WANs

16. H1 send a data to H2 R R H1 H H2 H1 to RA
To another Autonomous System H1 R RA RB
To another Autonomous System R
H1 to RA
IP address of H2 is not familiar, H1 must sent the data to the default getaway (RA)
H1 performs ARP request to obtain the default gateway MAC address
H1 sends an Ethernet frame to RA
Cengage Learning: Computer Networking from LANs to WANs

17. H1 send a data to H2 R R H1 H H2 RA to RB
To another Autonomous System H1 R RA RB
To another Autonomous System
RA to RB
RA ( ) examines the destination IP address and determines through a routing table lookup that the datagram must be forwarded to the RB ( )
If necessary perform ARP request to obtain the MAC address of RB
RA send Ethernet frame to RB R
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18. H1 send a data to H2 R R H1 H H2 RB to H2
To another Autonomous System H1 R RA RB
To another Autonomous System
RB to H2
RB( ) examines the destination IP address and determines that H2 is at is on the local Ethernet LAN.
Router perform ARP request to obtain the MAC address of H2
RB send Ethernet frame to H2 R
Cengage Learning: Computer Networking from LANs to WANs

19. Routing Processes: How Routes are Learned
Routing requires that every hop, or router, along the path to a packet's destination have a route to forward the packet.
Otherwise, the packet is dropped at that hop.
The routing table contains the information that a router uses in its packet forwarding decisions.
For an efficient routing decision, the routing table must represent the most accurate state of network pathways that the router can access.
Out-of-date information may cause the packet to be forwarded to the next- hop that is not very appropriate.
This may cause delays or packet loss.
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20. Cengage Learning: Computer Networking from LANs to WANs
Static Routing
In static routing, routes to remote networks are manually configured in the router.
Default routes are normally statically configured.
The decision on routes to be taken must be made by the network administrator.
The routes are chosen based on the network administrator’s knowledge about the internetwork structure.
The administrator will then configure the chosen routes into the router.
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21. Cengage Learning: Computer Networking from LANs to WANs
Static Routing
If the internetwork structure changes or if new networks become available, these changes have to be manually updated on the routers involved.
Static routing has a high administrative cost.
Network administrator has to actively monitor the network to see whether the configured routes are still valid and up-to-date.
If updating is not done in a timely fashion, the routing information may be incomplete or inaccurate.
This will result in packet delays and possible packet loss.
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22. Cengage Learning: Computer Networking from LANs to WANs
Static Routing
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23. Cengage Learning: Computer Networking from LANs to WANs
Dynamic Routing
In dynamic routing, routers learn routes automatically from other routers in the same internetwork.
Routers send routing updates to each other.
Routing messages are sent using a routing protocol.
Dynamic routing has higher processing and bandwidth overhead.
Due to the need send, receive and process routing messages.
However, once configured, the routers can manage routes themselves with little intervention from network administrators.
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24. Cengage Learning: Computer Networking from LANs to WANs
Dynamic Routing
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25. Cengage Learning: Computer Networking from LANs to WANs
Autonomous Systems
Autonomous System (AS) is network or group of networks and routers controlled by single administrative authority
Authority can be an institution, corporation or any organization
Registry Name
Region
AfriNIC
Africa
APNIC
Asia / Pacific
ARIN
North America
LACNIC
Latin American and Caribbean
RIPE NCC
Europe, Middle East and Central Asia
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26. Cengage Learning: Computer Networking from LANs to WANs
Autonomous Systems
Each AS is associated with AS number.
Number
Network
786
RIPE_ASNBLOCK-786
1842
USGS AS
3356
LEVEL3
4910
SPRINTNET NC
5727
WORLDNET-0
6453
TELEGLOBE AS
7739
AUTOWEB
8159
KANSASNET
10356
WINDYCITY
11834
DREXEL ASN
20001
ROADRUNNER-WEST
36599
NOAA-PACIFICREGION
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27. Cengage Learning: Computer Networking from LANs to WANs
Autonomous Systems
Each AS have single, clearly defined external routing policy
A new AS needs to be created if a network connects to more than one AS with different routing policies
Different routing protocols are used when
Routing inside AS – Interior Gateway Protocol
Routing between AS – Exterior Gateway Protocol
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28. Interior Gateway ProtocolH AS
EXTERIOR GATEWAY PROTOCOL
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29. Interior Gateway Protocol
Communication inside AS
Many protocols used as IGPs for IP networks
Gateway-to-Gateway Protocol (GGP)
Routing Information Protocol (RIP)
Routing Information Protocol 2 (RIP-2)
Interior Gateway Routing Protocol (IGRP)
Extended Interior Gateway Routing Protocol (EIGRP)
Open Shortest Path First (OSPF)
Intermediate System to Intermediate System (IS-IS)
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30. Exterior Gateway Protocol
Used between different Autonomous Systems (AS)
Define how networks within an AS advertise outside the AS
AS advertises “reachability” to connectable networks
Use Exterior Gateway Protocols (EGP) messages
Independent of IGPs used within Autonomous Systems
Facilitate exchange of routes between Autonomous Systems using different IGPs
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31. Exterior Gateway Protocol
Protocols used for EGPs in IP networks
Exterior Gateway Protocol (EGP)
Border Gateway Protocol (BGP)
Open Shortest Path First (OSPF)
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32. Interior Gateway Protocol Exterior Gateway Protocol
Table of summary
Interior Gateway Protocol
Exterior Gateway Protocol
Gateway-to-Gateway Protocol (GGP)
Exterior Gateway Protocol (EGP)
Routing Information Protocol (RIP)
Border Gateway Protocol (BGP)
Routing Information Protocol 2 (RIP-2)
Open Shortest Path First (OSPF)
Interior Gateway Routing Protocol (IGRP)
Extended Interior Gateway Routing Protocol (EIGRP)
Intermediate System to Intermediate System (IS-IS)
Cengage Learning: Computer Networking from LANs to WANs

33. Distance vector routing and Link state routing
Two classes of routing protocol :
Distance vector routing
RIP, Inter-Gateway Routing Protocol, Enhanced Inter-Gateway Routing Protocol
Link state routing
Cengage Learning: Computer Networking from LANs to WANs

34. Distance Vector Routing
Also called Bellman-Ford algorithm
Based on number of hops in a route between source and destination
Distance-vector routing algorithm
Each router sends entire routing table (to its neighbor) every 30 seconds
Distributed between network routers
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35. Distance Vector Routing
RIP ( a common distance vector protocol) uses UDP as transport protocol
Disadvantages
Bandwidth usage can become excessive
Difficult to debug, no security
Benefits
Runs on every router platform
Little effort to configure the RIP protocol
No computation, storage requirements
RIP-2 provides additional features
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36. Distance Vector Routing
Inter-Gateway Routing Protocol (IGRP)
Advance distance vector routing protocol
Cisco-proprietary solution to RIP issues
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37. Distance Vector Routing
Enhanced Inter-Gateway Routing Protocol (EIGRP)
Cisco-proprietary solution
Improves IGRP operating efficiency by using:
Distributed update algorithm, MD5 authentication, Protocol Independent Routing, CIDR support
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38. Cengage Learning: Computer Networking from LANs to WANs
Link-State Routing
Broadcasts cost of reaching each neighbor to all network routers
Creates consistent network view at routers
Method to compute shortest distance
Based on Dijkstra’s algorithm
Difference between distance-vector and link-state routing
Path with least hops may not be chosen as the least-cost route
100 a b 1 50 20 20 c d 20
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39. Cengage Learning: Computer Networking from LANs to WANs
Link-State Routing
Many routing protocols based on link-state algorithm
End System to Intermediate System
Intermediate System to Intermediate System
NetWare Link Services Protocol
Inter-Domain Routing Protocol
Exterior Gateway Protocol
Border Gateway Protocol
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40. Distance Vector Protocol
Table of summary
Distance Vector Protocol
Link-State Protocol
Routing Information Protocol (RIP)
Exterior Gateway Protocol (EGP)
Routing Information Protocol 2 (RIP-2)
Border Gateway Protocol (BGP)
Interior Gateway Routing Protocol (IGRP)
Open Shortest Path First (OSPF)
Extended Interior Gateway Routing Protocol (EIGRP)
Intermediate System to Intermediate System (IS-IS)
End-System to Intermediate System (ES-IS)
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41. Classless Inter-Domain Routing (CIDR)
Developed to recover unused class A and class B network addresses
Supported by interior and exterior gateway protocols
Based on route aggregation
Known as super-netting
Eliminates class concept
IP addresses and their subnet masks:
Written as four octets, separated by periods
Followed by a forward slash, two-digit number that represents subnet mask length
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42. Classless Inter-Domain Routing (CIDR)
Class B network
Class C super-net address in CIDR notation
/24
/24 indicates a 24 bit subnet mask
Route aggregation
Using several different routes so that a single route can be advertised
Minimizes routing table size
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43. Cengage Learning: Computer Networking from LANs to WANs
Policy Routing
Policy-based routing provides a tool for forwarding and routing data packets based on policies defined by network administrators
Primary use
Accommodates interconnected networks acceptable use policies
Routing based on factors other than “shortest path”
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44. Cengage Learning: Computer Networking from LANs to WANs
Policy Routing
Other considerations
Contract obligations
Quality of service (resource reservation)
Service provider selection
BGP supports policy-based routing
Complex set up and management
Great rewards
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45. Multi-Protocol Label Switching
Allows faster, cheaper IP routers
Based on ATM technology
Labels: shorter than IP addresses
Packets forwarded faster
IP address independent allowing for policies
Layer 2 network link information integrated into Layer 3 (IP)
Occurs within a particular Autonomous System
Simplifies, improves IP datagram exchange
Great flexibility to divert and route traffic
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46. Cengage Learning: Computer Networking from LANs to WANs
Summary
Basic differences between hubs and switches
2 switching techniques:
Store and forward
Cut-through
The function of the Spanning Tree Protocol in switched network
Basic differences between a switch and a router
Differences between distance-vector and link-state routing protocols
Classless Domain Internet Routing (CIDR) can increase the availability of Internet addresses
Cengage Learning: Computer Networking from LANs to WANs