1. WANs and Routers

2. Introduction to WANs
A wide-area network (WAN) is a data communications network spanning a large geographic area such as a state, province, or country.
Use transmission facilities provided by common carriers, for example, telephone companies.
It interconnects LANs that are usually separated by large geographic areas.
Operates at the physical layer and the data link layer of the OSI reference model (Typically)
See next slide

3. WAN Layers
The WAN physical layer describes the interface (electrical, mechanical, operational, and functional) between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). Typically, the DCE is the service provider and the DTE is the attached device.
The WAN data link layer protocols describe how frames are carried between systems on a single data link. They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services such as Frame Relay

4. 1. Physical Layer

5. 2. Data Link Encapsulations

6. DCE/DTE Interfaces DCE - Data Carrier Equipment
A modem interfaces to the outside carrier (Telco) equipment
It is the circuit terminating equipment
The DCE typically provides the serial clock signal
DTE – Data Terminal Equipment
The Router interfaces to the terminal equipment (user devices)

7. Wan Physical layer

8. WAN Devices Routers route between networks (LANS)
Provide slow speed serial WAN interfaces
Switches in the WAN
provide connectivity for voice, data, and video
Modems
Interface to voice-grade services
Analogue modems
Interface to digital services
Channel service units/digital service units (CSU/DSUs)
Communication servers
concentrate dial-in and dial-out user communication.

9. WAN Devices

11. Network Layer Path Determination
The two main functions of routers are
selection of best paths for incoming data packets,
switching packets to the proper outgoing interface.
Routers accomplish this by building routing tables and then exchanging their routing tables with other routers.
Routing tables can configured manually
But generally they are maintained dynamically by using a routing protocol that exchanges network topology (path) information with other routers.

12. Structure of the Internet

13. Structure of the Internet
The Internet is a network of autonomous systems, each of which has routers that typically play one of four roles.
Internal routers
internal to one area
Area border routers
connect two or more areas
Backbone routers
primary paths for traffic that is most often sourced from, and destined for, other networks
Autonomous system (AS) boundary routers
communicate with routers in other autonomous systems

14. Correctly Configured Internetwork
A correctly configured internetwork provides the following:
Consistent end-to-end addressing
Addresses that represent network topologies
Dynamic or static routing
Best Path Selection
Packet Switching

15. Router
A router contain a CPU, memory, a system bus, and various input/output interfaces.
Routers run an Internetwork Operating System software (IOS)
Routers have configuration files which contain system configuration settings
Routers run routing protocols, routers make decisions regarding the best path for packets.
The configuration file also contain routing protocol configuration settings

16. Router System Components

17. RAM is used for routing table information, fast switching cache running configuration, and packet queues.
Provides temporary memory for the configuration file of the router while the router is powered on
Loses content when router is powered down or restarted
NVRAM is used to store a backup/start-up configuration file
Retains content when router is powered down or restarted
Flash is used for storage of full Cisco IOS software images
Adding or replacing the flash Single In-Line Memory Modules (SIMMs) or PCMCIA cards can upgrade the amount of flash.
ROM is used for permanently storing start-up diagnostic code (ROM Monitor)
The main tasks for ROM are hardware diagnostics during router boot up and loading the Cisco IOS software from flash to RAM.
Some routers also have a scaled down version of the IOS that can be used as an alternative boot source.
Interfaces The interfaces are the router connections to the outside. local-area network (LANs), wide-area network (WANs), and Console/AUX.
Console/AUX ports provides physical access for initial configuration, These ports are not networking ports. They are used for terminal sessions from the communication ports on the computer or through a modem.
The WAN interfaces may be a fixed configuration or modular

18. Console and Auxiliary Ports
Console Port
Used for initial configuration
Is preferred over the auxiliary port for troubleshooting
it displays routers start-up, debugging, and error messages by default.
it can be used when the networking services have not been started or have failed .
it can also be used for disaster and password recovery.
Auxiliary Port
is an asynchronous serial maintenance port like the console port
but it is designed to interface to a modem for configured from a remote location

19. Console and Auxiliary Ports

20. Connecting Console Interfaces
Configure terminal emulation software on the PC for the following:
The appropriate com port
9600 baud
8 data bits
No parity
1 stop bit
No flow control
Connect a rollover cable to the router console port (RJ-45 connector).
Connect the other end of the rollover cable to the RJ-45 to DB-9 adapter
Attach the female DB-9 adapter to a PC serial comms port

21. WAN Types

22. Router Serial WAN Connectors

23. Introduction to Routers

24. Objectives
Operating Cisco IOS Software
Starting a router

25. Purpose of Cisco IOS Software 2.1.1
As with a computer, a router or switch cannot function without an operating system.
Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS
The Cisco IOS provides the following network services:
Basic routing and switching functions
Reliable and secure access to networked resources
Network scalability

26. Command Line Interface (CLI)

27. Router User Interface
The Cisco IOS software uses a command-line interface (CLI) as the traditional console environment
Access to the CLI is through several methods.
Console session
Use of a dialup connection using a modem connected to the router AUX port
Telnet to the router
To establish a Telnet session to the router, at least one interface must be configured with an IP address,

28. Router User Interface Modes 2.1.3
As a security feature the Cisco IOS software separates the EXEC sessions into two access levels.
User EXEC mode
Privileged EXEC mode.
also called enable mode.

29. Router User Interface Modes 2.1.3
User EXEC mode
Allows only a limited number of basic monitoring commands.
Is often referred to as a “view only” mode.
Does not allow any commands that might change the configuration of the router .
The user EXEC mode can be identified by the “>" prompt.
Privileged EXEC mode
Accesses all router commands.
This mode can be configured to require a password from the user before accessing it . For added protection, it can also be configured to require a user ID.
The privileged EXEC mode can be identified by the "#" prompt.

30. Cisco IOS Naming Conventions 2.1.4
The naming convention for the different Cisco IOS releases contains three parts:
The platform on which the image runs
The special features supported in the image
Where the image runs and whether it has been zipped or compressed

32. Show Version and Show Flash Commands 2.1.4
Before installing a new Cisco IOS software image on the router, check to see if the router has sufficient RAM and Flash memory for that image.
To check size of RAM, issue the show version
<output omitted>
Cisco 1721 (68380) processor (revision C) with 3584K/512K bytes of memory
To check size of flash memory, issue the show flash
<output omitted> bytes total ( bytes free)

33. Operation of Cisco IOS Software 2.1.5
The Cisco IOS devices have three distinct modes:
ROM monitor
Allows access to the Rom startup code which provides a basic text interface and limited functionality
Can only be accessed by a physical connection to the console port.
Performs the bootstrap process and provides diagnostics.
Can be used to recover from IOS corruption and to recover a lost password
Boot ROM
Like a PC the boot ROM provides the startup code to allow the file system (on the flash drive) to be read and the IOS loaded
Cisco IOS
The IOS is the operating system which is loaded from the flash drive into RAM and then executed
E-Lab:

34. Steps in Router Initialization 2.2.1
A router initializes by loading.
the bootstrap program
the operating system,
and a startup configuration file
If the router cannot find a configuration file, it enters setup mode
Setup is not intended as the mode for entering complex protocol features in the router
Upon completion of the setup mode a backup copy of the configuration file may be saved to nonvolatile RAM (NVRAM)
Step 1 -- The generic bootstrap loader, in ROM, executes on the CPU card. A bootstrap is a simple, preset operation to load instructions that in turn cause other instructions to be loaded into memory, or cause entry into other configuration modes.
Step 2 -- The operating system (Cisco IOS) can be found in one of several places. The location is disclosed in the boot field of the configuration register. If the boot field indicates a Flash, or network load, boot system commands in the configuration file indicate the exact location of the image.
Step 3 -- The operating system image is loaded. Then, when it is loaded and operational, the operating system locates the hardware and software components and lists the results on the console terminal.
Step 4 -- The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, set media characteristics, and so on.
Step 5 -- If no valid configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine referred to as the system configuration dialog, also called the setup dialog.

35. Default Sequence

36. Initial Sequence 2.2.1 When a Cisco router powers up,
it performs a Power-On Self Test (POST)
POST
Diagnostic program in the boot ROM that tests all hardware modules:
CPU, memory, and network interface ports

37. Router Initialisation
After the POST, the following events occur as the router initialises:
Step 1 The generic bootstrap loader in ROM executes
A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation .
Step 2 The IOS can be found in several places.
The boot field of the configuration register determines the location to be used in loading the IOS. If the boot field indicates a flash or network load, boot system commands in the configuration file indicate the exact name and location of the image.
Step 3 The operating system image is loaded.
Step 4 The configuration file is loaded from NVRAM
The configuration file saved in NVRAM is loaded into main memory (RAM) and executed one line at a time
Step 5 If no config found the IOS searches for a FTP server
Step 6 If no TFTP server found the setup dialog is initiated.

38. Router LED Indicators
Cisco routers use LED indicators to provide status information. Depending on the Cisco router model, the LED indicators vary.

39. Establishing a Hyperterminal Session 2.2.4
All Cisco routers include an EIA/TIA-232 asynchronous serial console port (RJ-45).
Cables and adapters are needed to connect a console terminal (an ASCII terminal or PC running terminal emulation software) to the console port.

40. Router Modes
User EXEC mode – Typical tasks include checking the router status. In this mode, router configuration changes are not allowed.
Privileged EXEC mode –Typical tasks include those that configure the router. You can also do what is available in User Exec mode.

41. Logging into the Router 2.2.5
prompt > type enable to enter privileged EXEC
Enter the privileged exec password that has been set with the enable secret
Two commands can be used to set a password for privileged EXEC mode:
enable password
enable secret – stronger (encrypted)
If both commands are used, the enable secret command takes precedence
prompt # now in privileged EXEC mode
To return to the user EXEC mode from the privileged EXEC mode, the
disable or
exit
Use ctrl-z Go directly back to enable mode from any mode

42. User Mode Commands
Typing a question mark (?) at the prompt displays a handy list of available commands
The "--More--" prompt at the bottom of the display indicates that multiple screens are available as output
The next available screen can be viewed by pressing the space bar
The next line only can be displayed by pressing the Return or Enter key
Press any other key to return to the prompt
The Tab key is used for auto completion
e-Labs:
2.2.6a Keyboard help in the CLI
2.2.6b IOS Auto-Completion

43. User Mode Help Commands (?)

44. Privileged Mode Help Commands

45. Help Command Example - clock set

46. The User Interface Error Indicator

47. Enhanced Editing

48. Using IOS Command history
With the history feature, the following tasks may be completed:
Set the command history buffer size
Recall commands
Disable the command history feature
The command history is enabled by default and the system records ten commands,
Terminal history size or the history size change the number of command lines the system records during a terminal session.
The maximum number of commands is 256
2.2.8 Drag and Drop: Router Command History

49. History Commands

50. The show version Command
IOS version and descriptive information
Bootstrap ROM version
Boot ROM version
Router up time
Last restart method
System image file and location
boot source
Router platform
Configuration register setting