Recovering Passwords of Cisco Router

When you forget the password, changing the configuration register will help you to get back and access router. Bit 6 in the configuration register tell the router whether to the contents of NVRAM to load a router configuration. But in the above example, the default configuration register value is 0x2102 which indicates that bit 6 is off. To recover a password, the user has to turn on bit 6. this indicates the router to ignore the NVRAM contents. When the bit 6 is turned on the configuration register value is 0x2142.

Important steps for password recovery are

1. Booting up a router and disrupting the boot sequence by pressing Ctrl+break.
2. Changing the configuration register to turn on bit 6.
3. Restarting the router and entering into privileged mode.
4. Copying the startup-config file to running-config and changing the password.
5. Changing the configuration register to the default value.
6. Saving the router configuration and rebooting the router.

Interrupting the router boot sequence

The first step in password recovery is to boot a router and perform break. This can be done by pressing Ctrl +Break key while using Hyper Terminal or when router first reboots. The following output is displayed when break is performed

System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
PC = 0xfff0a530, Vector = 0×500, SP = 0×680127b0
C2600 platform with 32768 Kbytes of main memory
PC = 0xfff0a530, Vector = 0×500, SP = 0×80004374
monitor: command “boot” aborted due to user interrupt
rommon 1 >

The rommon 1> prompt is used to recover password.

Changing the configuration register

Enter the command at the rommon 1> prompt to change the bit value on a Cisco 2600 series router:

rommon 1> confreg 0x2142,

To run new configuration, you have to reset the router.

After creating a break sequence on the router, type o to change the configuration register value on 2500 series router. This gives the configuration register option settings menu. To change the configuration register, type o/r command followed by new register value. Turning on bit 6 on Cisco 2502 router is as shown below

System Bootstrap, Version 11.0(10c), SOFTWARE
Copyright (c) 1986-1996 by cisco Systems
2500 processor with 14336 Kbytes of main memory
Abort at 0×1098FEC (PC)
>o
Configuration register = 0×2102 at last boot
Bit# Configuration register option settings:
15 Diagnostic mode disabled
14 IP broadcasts do not have network numbers
13 Boot default ROM software if network boot fails
12-11 Console speed is 9600 baud
10 IP broadcasts with ones
08 Break disabled
07 OEM disabled
06 Ignore configuration disabled
03-00 Boot file is cisco2-2500 (or ‘boot system’ command)
>o/r 0×2142

The last entry in the router output is 03-00 tells the router which IOS boot file is used. By default the router will use the first file located in the flash memory. Change the configuration register or use the system IOS-name command to boot a different file name.

Reloading the Router and Entering Privileged Mode

After changing the configuration register value, you have to reload the router. In this step, you have to reset the router

• From the 2600 router, type reset.
• From the 2500 router, type I.

The router will be reloaded and ask whether you want to enter setup mode. Enter No or press Enter to get into user mode and then type enable to enter privileged mode.

Viewing and Changing the configuration

Now you can see that we have passed the step where required to enter user mode and privileged mode password. In this step you have to copy startup-config file into the running- file config with the help of copy startup- conflg running- config or copy start run command. This helps you to enter into privileged mode. You can now view and change the configuration, but you cannot view enable secret password.

Type the commands as shown below to change the password.

Conflg t
enable secret <secret password>

Resetting the configuration Register and Reloading the Router

After changing the password, set the configuration register back to default values using config-register command:

Config t
Config-register 0x2102

Save the new configuration using copy running-config startup-config and reload the router.

Configuration register values of Cisco Devices

Cisco IOS is the kernel of Cisco routers and most switches. IOS was created to deliver network services an enable networked application. Almost ass Cisco routers run the same IOS but only about half of the switches currently run the Cisco IOS like Catalyst 1900 switch. Cisco IOS and configuration file reside in various locations in the Cisco device and it is very important to understand where these files are places and how they work. In this lesson, you will learn the commands which are used to load Cisco IOS on to the router and how to maintain backup files. In order to configure the Cisco internetwork, you need to understand some of the major components of router. The major components include ROM, RAM. Flash memory, NVRAM and config-register. The configuration register value tells the router to load IOS from the flash memory and it also tells the router to load the configuration from NVRAM. In this lesson, you will learn some of the commands used to verify and change the configuration register. Changing the configuration register value helps you to change the boot sequence and to recover the password. Here in this lesson you will find the steps used to recover the password.

Configuration register values

All Cisco routers have 16-bit software register which is written into NVRAM. The configuration register is set to load Cisco IOS from flash memory and to load startup-config file from NVRAM.

The router checks the system bootstrap information depending on the boot field setting in the configuration register. The default configuration register setting can be changed with the help of global configuration-mode command config-register.

In the below example the configuration register is set so that the router checks the startup file in NVRAM for boot system options. The configuration register is 16-bit register in NVRAM and the lowest 4 bits of the configuration register (bits 3, 2, 1 and 0) form the boot field. The default configuration setting on Cisco router is 0x2102. The 0x tells you that it is in hex and rest of the numbers are the actual settings. The easiest way to understand the configuration register is to convert the hex value into binary. Hexadecimal is base 16, which means that one of the 16 values can be represented with hexadecimal digit. The digits range from 0 through F, with 0 representing the decimal 0 and F representing decimal 15. To convert hex to binary, take each hex digit, convert it into decimal and then convert that into binary, as each hex digit represents four binary digits. The table below shows the conversion from hex to decimal to binary.

Conversions from Hex to decimal to Binary

HEX	DECIMAL	BINARY
0	0	0000
1	1	0001
2	2	0010
3	3	0011
4	4	0100
5	5	0101
6	6	0110
7	7	0111
8	8	1000
9	9	1001
A	10	1010
B	11	1011
C	12	1100
D	13	1101
E	14	1110
F	15	1111

So, if you want to change the default configuration register value 0x2102, first split the numbers into four individual digits and then convert each digit into binary and then put in correct order again. After converting, you can see that bit 13, 8 and 1 are on. In the table below, you can see that each set of 4 bits is read in binary with value 8, 4, 2 and 1.

Configuration Register Bit Numbers

Configuration Register Setting	Router Behavior
0x102	Ignores break 9600 console baud
0x1202	1200 baud rate
0x2101	Boots into bootstrap Ignores break Boots into ROM if initial boot fails 9600 console baud rate
0x2102	Ignores break Boots into ROM if initial boot fails 9600 console baud rate default value for most platforms
0x2120	Boots into ROMmon 19200 console speed
0x2122	Ignores break Boots into ROM if initial boot fails 19200 console baud rate
0x2124	NetBoot Ignores break Boots into ROM if initial boot fails 19200 console speed
0x2142	Ignores break Boots into ROM if initial boot fails 9600 console baud rate Ignores the contents of Non-Volatile RAM (NVRAM) (ignores configuration)
0x2902	Ignores break Boots into ROM if initial boot fails 4800 console baud rate
0x2922	Ignores break Boots into ROM if initial boot fails 38400 console baud rate
0x3122	Ignores break Boots into ROM if initial boot fails 57600 console baud rate
0x3902	Ignores break Boots into ROM if initial boot fails 2400 console baud rate
0x3922	Ignores break Boots into ROM if initial boot fails 115200 console baud rate

( If the value you have for the configuration register is not in the table, then determine which bits are set in order to compute the value )

The table below lists the software configuration bit meanings. You can see that the default value sets the router to boot to ROM if network boot fails (bit 13), disables the break function in bit 8 and sets the router to boot normally (bit 0-3).

Software configuration meanings

Bit Number	Hex	Meaning
00-03	0x0000-0x000F	Boots Field Parameters: 0x0000 - Stays at the system bootstrap prompt. 0x0001 - Boots the first system image in onboard Flash memory (EPROM). 0x0002-0x000F- Specifies a default netboot filename. Enables boot system commands that override the default netboot filename.
06	0x0040	Ignore NVRAM contents
07	0x0080	Disable boot messages
08	0x0100	Break disabled
10	0x0400	IP broadcast with all zeros
5,11,12	0x0020, 0x0800, 0x1000	Console line speed
13	0x2000	Boots default ROM software if network boot fails
14	0x4000	IP broadcasts do not have net numbers
15	0x8000	Enables diagnostic messages Ignores NVRAM contents

Note: Remember bit 4, 5 and 9 are reserved.

The boot field consists of bits 0-3 in the configuration register, controls the router boot sequence. Table describes the boot field bits.

The Boot system command

Value of boot field	Meaning	Description
0x---0	ROM Monitor mode	To boot to ROM monitor mode, set the configuration register value to 2100. You have to manually boot the router by using “b” command. The prompt will rommon >
0x---1	Boot image from ROM	To boot an IOS image stored in ROM, set the configuration register to 2011. The router shows the prompt router(boot)>
0x---2 to 0x---F	Specifies the default boot file name	Anyvalue from 2101 to 210F indicaes that the router use the boot commands speciies in NVRAM

Checking the current Configuration Register Value

The current value of the configuration register can be viewed by using show version command (sh version or sh ver). The show version command also displays the hardware configuration information, software version, names and sources of configuration file and boot image on a router. For example;

Router#show version
Cisco Internetwork Operating System Software 
IOS (tm) 2500 Software (C2500-JS-L), Version 12.1(5), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2000 by cisco Systems, Inc.
Compiled Wed 25-Oct-00 05:18 by cmong
Image text-base: 0x03071DB0, data-base: 0x00001000
ROM: System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-RXBOOT), Version 10.2(8a), RELEASE SOFTWARE (fc1)
Router uptime is 7 minutes
System returned to ROM by reload
System image file is "flash:c2500-js-l_121-5.bin"
cisco 2500 (68030) processor (revision D) with 16384K/2048K bytes of memory.
Processor board ID 03867477, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
1 Token Ring/IEEE 802.5 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2142

In this example, the configuration register value is 0x2102 and it is default setting. It indicates the router to look for the boot sequence in NVRAM. The show version command also gives the IOS version and in this example it is 12.1(5).

Changing the Configuration Register

Configuration register value can be changed to modify how router boots and runs. Configuration register value can be changed by using config-register command. The commands in the example below tell the router to boot a small IOS from ROM monitor mode and it also shows the current configuration register value.

Router#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#config
Router(config)#config-register 0x2102
Router(config)#end
Router#show version
Cisco Internetwork Operating System Software 
IOS (tm) 2500 Software (C2500-JS-L), Version 12.1(5), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2000 by cisco Systems, Inc.
Compiled Wed 25-Oct-00 05:18 by cmong
Image text-base: 0x03071DB0, data-base: 0x00001000
ROM: System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-RXBOOT), Version 10.2(8a), RELEASE SOFTWARE (fc1)
Router uptime is 11 minutes
System returned to ROM by reload
System image file is "flash:c2500-js-l_121-5.bin"
cisco 2500 (68030) processor (revision D) with 16384K/2048K bytes of memory.
Processor board ID 03867477, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
1 Token Ring/IEEE 802.5 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2142 (will be 0x2102 at next reload)

The new configuration register setting becomes active once the router reloads.

Router#reload
System configuration has been modified. Save? [yes/no]: n
Proceed with reload? [confirm]

Booting a Cisco Device

Before a router starts the booting process, it has to initialize its interfaces and then load the operating system and configuration file. To control this process the user has to find the type of image file and configuration file used by router.

When the router bots-up, the sequence of steps called as boot sequence occurs which helps to the hardware and load the required software. The boot sequence consists of following steps

Step 1: Power- on self-test: The router performs a POST is a series of hardware test that verify whether all components of the device are functional such as the POST. While performing this test the router also determines what hardware is present. The POST is stored in and executes from microcode in ROM.

Step 2: Load and run bootstrap code: The bootstrap code finds and loads Cisco IOS software. It is stored in ROM that is used to execute programs. The bootstrap program is responsible for finding the location of IOS software and then loading the file. By default, the IOS software is loaded from the flash memory in all Cisco routers. Once the IOS software is loaded, the bootstrap is not used until the router is reloaded.

Step 3: Load the IOS software: The configuration register and configuration file in NVRAM helps to determine the location of IOS image and helps to know the type of IOS image has to be used. Once it is found, the image is loaded into the RAM and starts the IOS running. Some of the router does not image from RAM but it executes directly from the Flash memory.

Step 4: Find the Configuration: The default is to look for a valid configuration file stored in NVRAM. It is also known as startup-fig.

Step 5: Load the configuration: If the stratup- config s in the NVRAM, is loaded and executed. If the startup-config is not found then the router will start the setup mode configuration upon boot up.

Using the setup command

If the router does not have a configuration file it will automatically enter Setup mode when you switch it on. Setup mode presents you with a prompted dialog called as the configuration dialog in which you can establish an initial configuration.

The prompts in the system configuration dialog of the startup command facilitate default answers inside the bracket [ ] following a question. Pressing Return key helps to use default. If the system has bee configured previously, then the default will be the currently configured values.

When the configuration process in the setup mode is completed, the configuration. When you enter “YES” the configuration will be executed and saved to NVRAM. If you enter “NO”, the configuration will not be saved and the process will start again

Setup Configuration Dialog

There are two options while using setup mode: Basic Management and Extended Setup. Basic Management only provides the configuration which allows to connect to the router but Extended setup provides the power to configure some global parameters in addition to this it also gives interface configuration parameters.

Setting global parameters

After checking the current interface summary, a prompt which signifies that the user has to enter global parameters for the router appears. These global parameters are nothing but the configuration values specified by the user.

The prompt appears as illustrated in the above figure...

The first global parameter which you can set is the host name. at initial configuration, the router name is displayed between the square brackets for example [Router]. The next global parameter is to set various passwords. First you have to enter enable password. When you enter the password characters for the prompt, Enter enable secret; the characters are then encrypted. This enhances the security of the password. Whenever you view the configuration file, the encrypted form of the password cannot be read.

Note: Enable secret password is secret word which is used instead of enable password when it exists. The “enable password” is used when “enable secret password” is not see.

Gathering Basic Routing Information

To get the basic information about router configuration, the user has to enter the commands at the CLI. The commands are generally the “show” commands. The show command cab be used o display configuration and parameters that is set.

For example:

Router#show clock

Typing Ctrl + Z will take back to global configuration mode. By using question mark (?) at any prompt you cab view list of all commands that are available and can be executed at that prompt.

Router(config)#?


gives all the commands which can be executed in the global configuration mode. This feature is referred as context-sensitive help. The question mark cab also be used to find commands which start with a certain letter. Like by typing c? at the prompt displays all the commands which start with the letter c.

Note: If you have typed an incorrect command, the caret symbol (^) and help response indicate the error. Notice that the caret symbol is displayed at the point in the command string where IOS detect an incorrect command, keyword. This error location allows you to find and correct syntax errors easily.

Show version command

The show version command is used to provide basic information on what type of Cisco IOS the router is using. In addition to this, it also gives information on system hardware, what software version you are using as well as the names, sources of configuration files and their boot images.

For example:

show version command

Basics of Cisco IOS

The IOS (Internetworking Operating System) runs on all Cisco routers and also some Cisco switches and allows you to configure the devices as well. This lesson starts to build a foundation for understanding the standard Cisco IOS. In this lesson, you will also learn the IOS modes of operation, syntax, storage and organization to better understand the array of options within IOS. In addition to this, you will also learn how to start a router for the first time by using correct commands and start-up sequence.

Definition of IOS

IOS (inter-networking Operating Systems )  is the operating system which controls all the functions of the devices such as access lists to queuing and provides the User Interface (UI) for managing the device. Generally, UI is the command line interface (CLI) in Cisco devices which is similar to other popular CLIs such as DOS and C shell in UNIX.

IOS version and structure

Cisco IOS is versioned using three numbers and some letters, in the general form a.b(c.d)e, where:

1. a is the major version number.
2. b is the minor version number.
3. c is the release number, which begins at one and increments as new releases in the same a.b train are released.
4. d (omitted from general releases) is the interim build number.
5. e (zero, one or two letters) is the release train identifier, such as none (which designates the mainline, see below), T (for Technology), E (for Enterprise), S (for Service provider), XA as a special functionality train, XB as a different special functionality train, etc.

Rebuilds : Often a rebuild is compiled to fix a single specific problem or vulnerability for a given IOS version. For example, 12.1(8)E14 is a Rebuild, the 14 denoting the 14th rebuild of 12.1(8)E. Rebuilds are produced to either quickly repair a defect, or to satisfy customers who do not want to upgrade to a later major revision because they may be running critical infrastructure on their devices, and hence prefer to minimize change and risk.

Interim releases : Are usually produced on a weekly basis, and form a roll-up of current development effort. The Cisco advisory web site may list more than one possible interim to fix an associated issue (the reason for this is unknown to the general public).

Maintenance releases : Rigorously tested releases that are made available and include enhancements and bug fixes. Cisco recommend upgrading to Maintenance releases where possible, over Interim and Rebuild releases.

The file naming convention is done by making use of the version of IOS and then adding all sorts of other specific information. The example, you may see an IOS image like this c4500-js40-120-3t-mz. To better understand this convention, read the steps below.

• The c4500 is for platform and it indicates that this image is for 4500 series router.
• The js40 indicates the feature set, in indicates that this image is for 4500 series router.
• The 120-3t is the version (12.0(3)T)
• M indicates that the software has to be executed from RAM.
• Z indicates that the file is zipped or compressed and it has to be decompressed into executable .bin format before loading into the device. A decompressed file is usually denoted with a 1.

Cisco Router IOS

Cisco internetwork Operating System was developed to deliver network services. IOS runs on most Cisco routers and on some Cisco switches such as catalyst 2950.

IOS of Cisco router is responsible for

• Carrying network protocols and
• Prevent unauthorized use of network.
• Providing network reliability for connecting to network resources.

Cisco ISO can be accessed through console port of a router, from a modem into the auxiliary port or even through Telnet.

Router Components

Cisco router use ROM and RAM similar to computers. Instead of hard drives, routers use special types of memory known as flash of NVRAM and these memories have unique function. The different types of memory include Random Access Memory, flash memory, Non-volatile memory and Read-Only Memory. Each of these are explained below

Random Access Memory (RAM) :

RAM is the only type of volatile memory in the router. With volatile memory, the contents are lost if the router loses power.

RAM contains a running copy of the Cisco IOS , which is loaded into RAM from the FLASH memory. It also contains the running copy of the configuration file which is loaded into the RAM from the NVRAM at start-up. In addition to this, it stores routing table, ARP tables and other data structures. RAM also provides packet buffering capabilities.

Non-volatile RAM (NVRAM) :

NVRAM (Nonvolatile RAM) is used to store the router’s startup configuration file and configuration register. It doesn’t lose data when power is switched off. So the contents of the start-up configuration file are maintained even when you switch off or restart the router

Flash Memory

Flash memory also holds a copy of IOS image. By flashing a new version on to the chip, this IOS image can be easily upgraded. Flash memory does not loss its contents when the router is switched off.

Read-Only Memory (ROM) :

ROM is used to store the router’s bootstrap start-up program, operating system software, and power-on diagnostic tests programs. ROM contains microcode for basic functions to start and maintain the router. RXBOOT is also contained in ROM. The table describes the major functions of Cisco router components.

Command-Line Interface (CLI IOS Command Modes)

IOS software uses a command-line (CLI as its traditional console environment. The
IOS interface is similar to a UNIX or DOS commands but the main difference is that IOS has a user interface with several command modes. Certain functions such as configuring a network interface can only be performed in a specific command mode. Each command mode permits to configure different configuration components.

User EXEC mode (user mode)

The first mode which is presented upon logging into the router is the user mode. In this mode, only a limited number of commands can be executed and no configuration parameters ca be read or modified. This mode will not help to perform any sort of debug and it does not contain informational (show) commands and also you cannot reconfigure device in any way. User mode helps to view some basic information such as routing table and the status of the components. In this mode, the prompt appears like this

Router> The greater than (>) symbol indicates that you are in user mode

Privileged EXEC Mode (enable mode)

The second mode is the privilege mode which is also known as enable mode. This mode allows users to view the system configuration, restart the system and enter configuration mode. It allows you to access all commands usable by the device and allows all the commands that are available in user mode.

To enter into the enable mode, type enable command which will ask for password (if password is set). This password will be either the enable secret of enable password. The user has to enter correct password or secret password to access privileged mode. Enable secret password will be in encrypted form when it is stored in the configuration and it is safer. Once you enter into the enable mode, the prompt will be changed to # sign it will be as shown below

Router>enable

Password:

Router#

In the privileged mode, you can use any standard commands such as show command and debug command. Debug command are special commands used to perform advanced diagnostics on the system. Few other configuration commands such as clear, clock, reload, copy and erase can be used in privilege mode. To exit the privileged mode, the user has to enter disable command.

To configure parameters of the router, one needs to proceed from privileged EXEC mode to the global configuration mode.

Global Configuration Mode

By typing configure terminal takes user to the global configurations mode from the enable mode which helps to configure the device. This mode allows users to modify the running system configuration. Once the user enter into the configuration mode, the prompt again changes which can be illustrated as shown below

Router # configure terminal

Router(config)#

This is also known as global configuration mode because all the commands used here will have an affect on the entire device.

Global configuration mode consists of sub modes  such as interface mode and line mode. As the configuration sub-modes changes depending on what is being configured, the words within the parenthesis also changes for example: when user enters interface configuration sub-mode, the prompt changes to (config-if)# following the router name.

To exit configuration mode, the user can enter end or press Ctrl+Z

Interface Mode

The commands entered in this mode affect the current interface only. Interface command can be used to modify the configuration of a specific interface. In order to perform any change enter into global configuration mode:

Router 1 (config)# interface serial 0

OR

Router 1 (config)# int serial 0

The result will be:

Router 1 (config-if)#

The prompt changes to Router (config-if) # which indicates that you are in interface configuration mode.

Line Mode

Line command helps to configure user-mode passwords. The prompt then changes to Route (config-line)#;

Router (config)# line con 0

OR

Router 1 (config)line vty 0 4

The result will be:

Router 1 (config-line)#

The line console 0 commands are called as major command and it is also known as global command. The commands which are entered from (config-line) prompt are known as global command.

Each mode is represented by a different prompt, as show in the table below:-

Command mode

Command and mode	Prompt	Command to enter mode
User EXEC	Router>	Login
Privileged EXEC	Router#	Enable
Global Configuration	Router(config)#	Configure terminal
Interface Configuration	Router(config-if)#	Interface type number ( from the global configuration mode )
Line Configuration	Router(config-line)#	Line line_type line_number editing_line_number ( from global configuration mode )

Enhanced Editing Commands and History Commands

The user interface contains an enhanced editing mode that provides a set of editing key functions. No terminal editing command at the privileged mode helps to disable advanced editing features. You can also re-enable these features bu using terminal editing command. The table below shows some of the editing commands and how it can be helpful while working on router

Editing commands

Command	Meaning
Ctrl+A	Will take cursor to the beginning of the current line
Ctrl+E	Moves the cursor to the end of the line
Esc+B	Moves back one word
Ctrl+B	Moves back one character
Ctrl+F	Move forward one character
Esc+F	Moves forward one character
Ctrl+D	Deleted the single character
Backspace	Removes one character to the left of the cursor
Ctrl+R	Redisplays a line
Ctrl+U	Erases a line
Ctrl+W	Erases a word
Ctrl+Z	Ends configuration mode and returns to EXEC mode

Router Command History

Router command history will shown the commands which are typed previously. The history size can be changed and it can be verified by using show terminal command. The table below shows the router command history with the commands:

Command	Meaning
Ctrl+P or up arrow	Shows last command entered
Ctrl+N or down arrow	Shows previous command entered
show history	Shows last 10 commands typed by default
show terminal	Shows terminal configuration and history buffer size
terminal history size	Changes buffer size but the maximum size is 256

Cabling WAN - Part II

Physical Layer Implementations in WAN

Most physical implementation transmits data or traffic across WAN (wide Area Network). The requirement for physical implementation depends on distance of the equipment from the speed and the services itself. The selection of type of physical layer depends on distance. Speed and type of interface required to connect.

Figure below shows the lists of subset of the physical implementation which support most commonly used WAN solutions.

WAN Physical Layer Implementations

 Serial connections are used to support wireless serial such as dedicated leased lines that run point-to-point protocol (PPP), High-Level Data Link control (HDLC) or Frame Relay. The speed of the connection varies from 56kbps to T1/E1 (1.544/2.048 Mbps).ISDN (Integrated Services Digital Network) offer dial-on-demand connections or dial backup services. ISDN BRI (Basic Rate Interface) is made up of two 64kbps Bearer channel (B channel)for data and one 16kbs Delta channel (D channel) for signaling and other link management tasks. Point-to-point protocol is transmit data over B channel.

Difference between WAN serial connections

Long distance communication in WAN is performed using serial transmission. Serial transmission is a process in which bits are sent over single channel. Unlike parallel data transmitted at a time, serial transmission is one-at-a time transmission. This provides more reliably long distance communication. Serial channels employ electromagnetic or optical frequency range to carry bits.

The Frequency defined in terms of cycles per second (Hertz), function as band or spectrum required for communication. For example: the frequency of signals send over voice grade telephone lines is 3 kHz. The size of the frequency is also known as bandwidth.

Various types of physical connection enable to connect to serial WAN services. Depending on the selection of physical implementation given by the service provider, the type of serial cable to be used with router has to be selected.

Figure shows different type of serial connector

WAN Serial Connections Types

For Cisco router, physical connectivity at the customer site is provided by one of the two types of serial connectors. The first type of serial connection is 60-pin connector which is commonly used by Cisco routers. This indicates that the router end of most adapter cable use male 60-pin connector, so the network ends of the adapter cables has to match with particular WAN service hardware.



Bandwidth can also be expressed as bits per second (bps)which indicate the quantity of data in bits transmitted by using two physical layer implementation (EIA/TIA-232 and EIA/TIA-449). Table below shows the physical standards for WAN serial connections.

Cabling Routers for serial connections

In addition to determining cable type, one more factor which is very much essential is to determine whether the device is Data-terminal Equipment (DTE) or Data Circuit-terminating Equipment (DTE) device. These are the two types of devices that can communicate over serial interface. DCE provides physical connection to the network and forwards the data to the service provider.

If the connection is made directly to a service provider or a device that provides signal clocking such as channel or data service unit (CSU/DSU), the router will be data terminal equipment (DTE) and uses a DTE serial cable. Figure below shows DTE/DCE connections. In this example router which is DTE device is connected to CSU/DSU or modem, which are DCE devices. As the serial devices are DCE, DTE cable has to be used to connect router and CSU/DSU or modem.

DTE/DCE Connections

DTE/DCE Connections

In some cases router is required to provide the signal clocking, so it will use data communication equipment (DCE) signal cable. For example when performing back-to-back router scenario in a test environment, one router is DTE and other router is DCE.
When router has to be cabled in a serial connectivity, it may have fixed or modular ports. The type of ports either fixed or modular will have impact on the syntax which will be used to configure each interface.

Cisco 2500 Router

Figure shows an example of 2500 Router with fixed port. Each port is assigned with port type and port number for example “serial 0”. In order to configure fixed interface has to be specified using this convention.

Fixed serial ports on 2500 router

Routers with modular serial ports are also available. Typically, each port is assigned a label of port type, slot number and port number. In order to configure port on modular card, interfaces are specified using this convention:


<Port type><slot number>/<port number>. For example serial 1/0

Note: port designation convention changes with type of router used. For example: 7500 series router has virtual interface processor. The convention of this also include VIP slot

<Port type><slot number>/<port adapter number>/<port number> (serial 1/0/0)

Note: Using label of port type and port number such as serial 0, you can configure 1603 router (which both fixed and modular serial interface) as fixed interface.

Cabling Router for ISDN BRI connection

ISDN BRI standard defines several physical wiring interfaces, but the two common types of interfaces are BRI U-Interface and BRI S/T interface. U-Interface is the 2-wire interface provided by the service provider for connection to the NTI.U-Interface has built- in internal NT-1 devices. The S/T –interface is the 4-wire interface between NT1 and the ISDU networking equipment such as router. An S/ T interface is used when NT1 is a separate device. The type of interface required is determined depending on whether service provider will provide an NT1 device.NT1 refers to network termination type 1 device.

NTI is a simple  device that serves as an interface between router and ISDN equipment and it is used to connect four wire subscribes wiring to two-wire local loop.

Category 5 straight-through cables are required to interconnect ISDN BRI port to the service provider device

Note: cables from ISDN BRI port has to be properly inserted only to ISDN jack or switch. Because ISDN BRI uses high voltage and it may  effect non-ISDN devices



Setting up console  connection                       

To initially configure Cisco device, management connection has to be directly provided to a device. This management attachment is nothing but console port. Console port enables to configure Cisco hub, switch or router. The type of cable used to connect a console port and terminal is rollover or console cable with RJ-45 connector.

Figure below shows connecting device using console cable.

Steps to connect computer to console port:

Step 1: connect the device to the computer using console cable. RJ-45 to DB-9 or RJ-45 to DB-25 adapter may be required for computer or terminal.

Step 2: configure terminal emulation software for computer with above a default COM port settings: 9600bps, 8 data bits, no parity, 1 stop bit and no flow control.

Cabling WAN - Part I

The physical elements of router such as interfaces help to other terminals. In this lesson, you will learn the features of different types of physical interfaces such as console port, auxiliary port, Ethernet interface, serial port and modular interfaces. Ethernet interface is used to connect to Ethernet network and auxiliary ports are used to connect a modem to router. Modular interface allows to add new interface cards without a need to purchase a new router.

A connection between one networks to another some times make use of WAN services. These WAN services utilize various types of connection and cabling methods which is very much different from those of LAVs. So it is very important to understand the type of cabling required to connect to these services. In this lesson, you will learn the process of connecting Cisco devices to a terminal which enables to configure and monitor devices.

Physical Interfaces

A router has several physical interfaces which enables it to connect to different types of network media and terminals. The terms port and interfaces can be used interchangeably. Some of the physical interfaces normally found on Cisco router are listed below.

Console port

Console port is a point where you connect computer or terminal to router to access operating system. While connecting to the router console port is very much essential to configure other interfaces. ASCII terminal is the most commonly used computer running terminal emulation software for example Hyper Terminal in windows 98 can be connected to console port. Console port. Console port provides access to the command interpreter, so that it can be used to configure and maintain router.

Console cable is an asynchronous serial interface which uses RJ-45 connector and looks same phone jack but slightly larger. Adapters are also available which is required for connections to PC terminals, modems and other external communication equipment. RJ-45 crossover or console cable is required to connect computer or a laptop to router. Depending upon the size of the PC serial port, you rewire either RJ-45 to DB-9 female adapter or RJ-45 to DB-25 female adapter.

Cable pinout for: Cisco Console RJ45 to DB9 Pin

Use this cable to configure a Cisco router through the Console port at the router. 

This cable is also suitable to be used with Sun T2000. 

Console cable can be identified by comparing the modular ends of the cable. The wire connected to the pin on the outside of the left connector (pin 1) must have same color as the pin on the outside of the right connector (pin 8).  In Cisco cables, pin 1 is white on one connector and pin8 is white on the other connector.

Table shows the RJ-45 console cable pinouts

The default parameters for the console port are

• 9600 bits per second.
• 8 data bits
• No parity generated or checked.
• 1 stop bits

Auxiliary Port

Auxiliary (AUX) port is an asynchronous serial port which looks same as console port. Auxiliary port is used to connect modem to the router. The main difference between console port and auxiliary port provides hardware flow control enabling synchronized communication between sending and receiving device. When the buffer on receiving device gets full, it sends a message to the sending device asking to stop transmission speeds than terminal devices. Auxiliary port is suitable for high speed modem connection and the maximum speed is 38,400bps.

In order to connect auxiliary port to a modem, RJ-45 crossover cable is required. And RJ-45 to DB-25 male adaptor which is very compatible with the modems can be used.

Ethernet Interface

The Ethernet Interface is used to connect a router to a LAN and it is most common interface on a Cisco router. Ethernet interface uses RJ-45 connector or it may use 15-pin Attachment Unit Interface (AUI) connector Cisco routers are available with either 10 megabit or 100 megabit Ethernet interface. Cisco routers are also available in different configuration with either one or several Ethernet interface.

In some cases, you need to hook Ethernet interface to 10BaseT hub or switch. For this, you require AUI connector to 10BaseT transceiver.

Serial port

Serial port is an interface which is used to connect WAN links either a leased line or T1.Maximum speed at which the Cisco router’s serial port may operate is 115,200kbps. A router’s serial port is different from PC’s serial port. A router’s serial ports are synchronous which operate at higher speed than PC’s serial port.  PC’s serial ports are asynchronous. Serial port can be directly connected to Data communication Equipment for example Channel service Unit/Data Service Unit (CSU/DSU). A CSU/DSU which is required on both the ends of dedicated leased line is a high powered modem. The selection of cable type depends on DCE device. In lab environment, wide Area Network (WAN) can be simulated by directly connecting two serial ports using DCE/DTE cable.

Modular Interfaces

Most of the Cisco routers such as 3600 serial, 2600 serial have modular interface. Modular interface is an empty slot which enables to plug any other type interface. Serial and Ethernet interface can be added. Modular interface are available in various type such as Integrated Services Digital Network (ISDN), Frame Relay any voice interface cards. For T1 and ISDN lines, the modular interfaces have built-on CSU/DSUs and NT1s respectively which eliminates the need of additional router and line.

Note: The devices in synchronous communication synchronize by constantly transmitting bits over a wire or line. In synchronous communication, when there is data devices simply send idle characters to continue the synchronization. In asynchronous communication, a start bit and stop bit are added to each segment. For synchronous communication, both start and stop bits are eliminated, so faster transmission speed is achieved.

Cabling LAN - Part II

Crossover Cables & straight Through Cables

Ethernet cables can be wired in three different ways. The two main ways are straight through and Cross over. The third type is called as Rolled. Straight through cables are generally used to connect different types of equipment; for example, a computer  and a hub. Crossover cables are generally used to connect similar types of equipment like a computer to another computer. Inside the UTP cable there are 8 physical wires. The 8 wires are arranged in pairs: one pair is used to send information and other pair is used to receive information. For computers to communicate, the sending pair of one computer has to be connected to receiving pair of another computer. So crossover cables are required.

T568B Termination T568A Termination

RJ45 Jack

Straight-through Cable

The straight- through cable is used to connect:

• Host to switch or hub
• Router to switch or hub

Straight through Cable

Straight Through Cable

In the above figure you can see only 1,2,3 and 6 pins are used. Connect pin 1 to pin 1,2 to 2,3 to 3 and 6 to 6. Remember this would be an Ethernet cable and it will not work with voice, Token Ring, and ISDN.

Crossover cable

The Crossover cable be used to connect:

• Switch to switch
• Hub to hub
• Host to host
• Hub to switch
• Router direct to host

Same four wires are used in the cable as in the straight-through cable but different pins are connected together. In the  following figure, can see how four wires are used in crossover Ethernet cable. And notice that instead of connecting 1to1, 2to2 etc, pins 1 is connected 3, pin 2 is connected to 6 on each side of the cable.

Crossover cable pinouts

Two pairs crossed, two pairs uncrossed

Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 (pins 4, 5, 7 and 8) remain un-crossed.

T568A  - All Four Pairs Crossed

T568B  - All Four Pairs Crossed

Rolled cable

Roll Over or Console Cable

Rolled cables are not used to connect any Ethernet connections together, but rolled Ethernet cable can be used to connect a host to a router console serial communication port. Rolled cable is also used to connect PC running Hyper- Terminal to the Cisco hardware. Eight wires are used in rolled cable to connect serial devices, although not all eight are  used to send information just as in Ethernet networking. Figure below shows eight cables used in a rolled cable.

Cabling LAN - Part I

In a network, a machine has to be connected to at least other machine, through metal cabling, fiber-optic cabling or radio waves. Even new technologies such as radio based networks and infrared light based networks produce new ways of connecting two devices to each other, but least expensive and most popular medium for networking is still copper wires.

Cables use copper wires to transmit electrical signals or fiber optic to transfer optical light signals. Cabling is also called as wiring because copper wire is used in greater part in the network cables. Electrical signal, which is transmitted through cable, generate magnetic field and radio frequency interfaces. When cables are used, the electrical signal emits radiation, which may interfere with other signals. When this happens it is called as cross talk. In order to overcome this, metallic wires are manufactured in such a way that it reduces the effects of radiation and interference. The wires, which are close to one another, can interfere with the transmission, changing the electrical signal and can cause bit error. Because of interference, cables produce emission and are susceptible to nearby cables. The popular way to reduce these effects of emission is to send the information, through a pair of wires and to twist the pair of wires together, Using an opposite current on each wire generates magnetic field but in opposite

direction. So by twisting the wires, the two magnetic fields cancel each other. Another popular way to reduce emissions of copper cables is to shield the wires by some material which blocks electromagnetic radiation. Shielding the wires makes the cables less flexible and increases material and manufacturing costs. In this lesson, you will learn some of the cable type, its uses and features.

Cabling types

A wide range of cabling types has been used to connect Ethernet systems. Network uses three types of cables: coaxial, twisted and fiber optic cables. Twisted pair is similar to telephone cable. It consists of pairs of cables twisted around each other to reduce electrical interference. For high speed and high secure systems, Fiber optic cables are used. However, it is less commonly used, as the cable is expensive and more difficult to install.

1. Unshielded Twisted Pair (UTP) Cable
2. Shielded Twisted Pair (STP) Cable
3. Coaxial Cable
4. Fiber Optic Cable

Twisted Pair Cables:

Twisted pair cable is a type of cable, which consists of two independently insulated wires around one another. The use of twisted pairs helps to reduce crosstalk and electromagnetic induction. High quality twisted pair cables have 1to 3 twists per inch. Twisted pair cables is the ordinary copper wire which is used to connect most of the home and business computers to Telephone company. Each wire in twisted pair cables has color plastic insulation attached to it. Twisted-pair cables are lighter, thinner, more flexible and easier to install than coaxial and fiber-optic cabled. There are two types of twisted pairs: Unshielded twisted pair and shielded twisted pair.

Shielded Twisted pair (STP):
The twisted pair in STP are individually wrapped in a foil shield and enclosed in an outer braided wire shield. The shielding is designed to minimize electromagnetic radiation and susceptibility to crosstalk. Each pair is surrounded by insulating material, with another insulator covering all pairs together. The extra material makes the cable white bulky and cause lack of flexibility. Shielded twisted pair cables are commonly used on networks using Token Ring topology.

Unshielded Twisted Pair (UTP):
Unshielded Twisted pair cable is the most popular of all the cable types. UTP cables are used not only for networking but also for traditional telephone (UTP) cable consists of four pairs of wires inside the jacket. Each wire has some colored plastic insulation attached to it. As copper wire is smaller in diameter, it may break easily. So, a thin plastic insulation provides more strength to each individual wire. Each pair has different twists per inch, which helps to eliminate interference from adjacent pairs or from other electrical devices.

Unshielded Twisted pairs standards

A great many different cabling standards exist. EIA/TIA (Electronic Industries Association / Telecommunications Information Association) standard  568A is one of several standard that specify “Categories” of unshielded twisted pair cabling systems in terms of data rates that they can carry. Under UTP type of cables for Ethernet wiring, the categories number. For computer networks the most common are category5, category5e and category6

CATI (category1) is typically used for telephone wire. This type of wire is not capable of supporting network traffic and it is twisted. CATI is not suitable to use with Ethernet. Only telephone companies who provide ISDN use it. There fore, the wiring between the customer’s site and Phone Company’s network use CATI cable.

CAT2 is used most commonly used for token ring networks, supporting speeds up to 4 Mbps. For higher speeds (100 Mbps) CAT5 cables are suitable. CAT3, CAT4 andCAT5 cables are generally 4 pairs of twisted copper wires. CAT5 has more twists per inch than CAT3, therefore it can run at higher speeds and greater lengths. CAT3 and CAT4 are also used for token ring networks. Category5e is a new standard that will specify transmission performance, which exceeds CAT5. Like CAT5, it consists of unshielded twisted pair with 100-ohm impudence and electrical characteristics supporting at frequencies up to 100MHz. CAT6 wire was originally designed to support multi gigabyte Ethernet. It is similar to CAT5 but contains a physical separator between the four pairs to further reduce electromagnetic interference. CAT7 is a proposed standard that aims to support transmission at frequencies up to 600MHz over 100 ohm twisted pair.

Most common cable categories

Category	Bandwidth	Applications	Notes
Cat1	0.4 MHz	Telephone and modem lines	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat2	? MHz	Older terminal systems, e.g. IBM 3270	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat3	16MHz	10BASE-T and 100BASE-T4 Ethernet	Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s.
Cat4	20MHz	16 Mbit/s Token Ring
Cat5	100MHz	100BASE-TX & 1000BASE-T Ethernet
Cat5e	100MHz	100BASE-TX & 1000BASE-T Ethernet	Enhanced Cat5. Practically the same as Cat5, but with better testing standards so Gigabit Ethernet works reliably.
Cat6	250MHz	1000BASE-T Ethernet	Most commonly installed cable in Finland according to the 2002 standard. SFS-EN 50173-1
Cat6e	250MHz (500MHz according to some)	10GBASE-T (under development) Ethernet	Not a standard; a cable maker's own label.
Cat6a	500MHz	10GBASE-T (under development) Ethernet	Standard under development (ISO/IEC 11801:2002 Amendment 2).
Cat7	600MHz	No applications yet.	Four pairs, U/FTP (shielded pairs). Standard under development.
Cat7a	1200MHz	Telephone, CATV, 1000BASE-T in the same cable.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.
Cat8	1200MHz	Under development, no applications yet.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.

Coaxial cable

Coaxial cable is a type of communication transmission cable in which solid center conductor is surrounded by an insulating medium, which is surrounded by tubular outer conductor (foil). The entire assembly is then surrounded with an insulating and protective outer layer. Coaxial cables are capable of carrying many data, voice and video conversations simultaneously. The two type of coaxial cabling used with Ethernet are.

• Thicket
• Thinnet

Thicket

Thicket coaxial is used with Ethernet 10BASE5 network, which supports a 100Mbps transmission rata and consists of 500 meter segment length. Thick Ethernet consists of mark at every 2.5 meters, which  indicates proper placement of 10Base5 transceivers used to connect  stations to the network Transceiver placed at any multiple of 2.5 meters intervals minimizes signal reflection, which may spoil the transmission quality in the cable. Vampire tap is used to connect  to the segment. Vampire tap is piece of metal, which is cylindrical in shape when tap is closed. When tap is closed around the cable, it is pushed through the shielding to provide the metal in the vampire tap to touch the copper wire inside the cable.

Thinnet

Thinnet coaxial cable is used with Ethernet 10 Base2 networks. Compared to thicknet cables, thicknet are cheaper, Lighter, flexible and easier to install. It consists of 185 meter maximum segment Length. 10Base2 transceiver is connected to the thinnet cable segment through “BNC (British Naval Connector) T” connector. To connect to computer, one end of T connector plugs directly into Ethernet card in the computer station, another end is plugged into cable from upstream cable, and another cable attached to next device downstream.

10Base5 and 10Base2 Connectors

Transceiver is a term formed by combining the terms transmitter and receiver. Instead of Ethernet card, it consists of electronics that send and receive signal on the Ethernet cable.
Disadvantages of coaxial cable includes that are more expensive, heavier and relatively inflexible. Also, when it is used for Ethernet, a single break in cable causes the failure of entire segment.

Fiber-Optic Cable

An optical fiber breakout cable

A multi-fiber cable

Fiber-optic cabling is a technology in which the electrical signal is converted into optical signal that is transmitted through a thin glass fiber and it is converted back into electrical signal. The figure below shows the components of a fiber-optic cable.


Fiber-optic cable is made from fiberglass and it does not break easily. The plastic and Kevlar coating provides more strength to the fiber glass. Kevlar is the material that most of bullet proof vests is made of.

Fiber-optic cable consists of two concentric layers of high-purity silica glass- the core and the cladding. The “core” is the inner part of an optical fiber through which light is transmitted. The “cladding” is the material in the middle layer. The light stays confined to the core because the cladding has lower refractive index than the core, which means that when light hits the outer wall, it is reflected back to core. The outer protective layer serves to protect core and cladding from damage.

The devices such as Ethernet switches, which are at the end of the cable, generate optical light signal. These signals travel through the optical fiber in the canter of cable. Electricity is not used across the cable; only light is transmitted.

Optical fiber connector

FC connector	MIC (FDDI) connector
LC connector	MT-RJ connector
LuxCis connector	SC connector
ST connector