1. Router Basics
MM Clements

2. Introduction WAN introduction and devices MODEM technologies
Router Functions
Router Hardware
Connecting to a router for the first time
4/26/2017
ITCN

3. Router Function Linking WANs and LANs
Interconnecting communication lines
Path determination and packet switching
Application of security rules (ACLs)
Protocol conversion (encapsulation)
E.g. HDLC, PPP etc.
4/26/2017
ITCN

4. Introduction to WANs
A wide area network (WAN) is a data communications network spanning a large geographic area such as a region, country or the entire planet
A WAN may interconnect LANs
May use microwave, satellite, fibre-optic, phone lines etc. to cover distances
4/26/2017
ITCN

5. WAN Devices Switch connects PCs, servers etc. to a router
Ethernet cannot travel large distances so MODEM is used
MODEM terminates a data circuit – data circuit-terminating equipment (DCE)
Communication server allows many users access to a MODEM link
4/26/2017
ITCN

6. Use of MODEM in WANs MODEM = Modulator and Demodulator
Translates between Ethernet and WAN technology and back again
Permits long distance communications
4/26/2017
ITCN

7. Routers Connected by WAN Technologies
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ITCN

8. Some WAN Terminologies
T1=1.544 Mbps, T3= Mbps , X.25, SMDS (SWITCHED MULTIMEGABIT DATA SERVICE), ATM, xDSL, Modem, Cable Modem, ISDN, OC-x
X.25 and ISDN are used less today than in the past but can still be found in operation
4/26/2017
ITCN

9. Cisco Routers
Operating system is known as Internetwork Operating System (IOS)
Held in Flash memory (non-volatile)
CLI not GUI
Based on UNIX heritage
4/26/2017
ITCN

10. Router Operation Layer 3 device Accepts PDUs on incoming network
Examines PDU data
Makes decision(s) for next stage of PDU journey
May modify PDU contents (not payload)
Passes PDU on to outgoing network
4/26/2017
ITCN

11. Router Sorts Incoming Traffic
Acts like Internet roundabout
Allows data to get closer to its destination
Best path decision made by router
Incoming packets are switched to the most appropriate outgoing network
4/26/2017
ITCN

12. Data Link Layer and Routing
Router does not pass on layer 2 data
e.g. broadcasts do not pass router
Layer 2 header is modified by router
Source and destination MAC addresses are changed at each router
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ITCN

13. Network Path Determination
Router accepts packet and views inside Network Layer header
IP address of destination carried in Network Layer header and other information
Destination IP address looked up in routing table
Packet passed to appropriate exit interface
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ITCN

14. Transport Layer Determination
Transport Layer header contents examined
Source and destination port checked
May trigger security of an Access Control List
May drop packets under heavy load
UDP often first casualty
4/26/2017
ITCN

15. Access Control Lists Used to identify incoming packets
Can be used for security purposes
E.g. do not allow TELNET traffic
Identified by destination port number 23
Found in Transport Layer header
More on ACLs later in course
4/26/2017
ITCN

16. Inside a Router Router is a dedicated computer
Contains hardware found in most PCs
Does not have hard disk – Flash memory is used instead to hold IOS
NVRAM used to hold configuration files
DRAM used to hold routing tables, buffering, ARP cache etc
CPU, ROM and interfaces too
4/26/2017
ITCN

17. Internal Components of a 2600 Router
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ITCN

18. External Connections Configuration connections LAN connections
Console and AUX
LAN connections
FastEthernet (usually)
WAN connections – often via WAN Interface Cards (WICs)
Newer hardware is modular
Makes upgrading cheaper
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ITCN

19. External Connections on a Router
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20. Router Connections
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ITCN

21. 9600 baud 8 data bits 1 stop bit No parity No flow control
Connecting to a Router
First-time connection must be via console cable attached to a PC
PC runs terminal emulator e.g. Hyperterminal
Correct parameters must be set
9600 baud  8 data bits  1 stop bit  No parity  No flow control
4/26/2017
ITCN

22. Physical Connection to Router
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ITCN

23. Conclusion Routers choose paths and switch data packets
IOS runs on Cisco hardware
Apply security etc.
No hard disk – all solid state
New routers have modular chassis for flexibility
Terminal emulator and rollover cable to connect
4/26/2017
ITCN