All things about CISCO IOS

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All things about CISCO IOS

Posted by Unknown Monday, January 28, 2013 0 comments

We will cover all important points regarding CISCO IOS- Cisco Internetworking Operating System, that are commonly asked on a CCNA exam. So let`s start from the beginning:

When you log into a CISCO router:

Router>	User EXEC mode
Router#	Privileged EXEC mode
Router(config)#	Configuration mode
Router(config-if)#	Interface level (within configuration mode)
Router(config-router)#	Routing engine level (within configuration mode)
Router(config-line)#	Line level (vty, tty, async) within configuration mode

Running configurations reside on RAM, we issue copy running-config startup-config command to move the configs from RAM to NVRAM or in simple words to save it. To load configs from a TFTP server we use copy TFTP: running-config command.

When you turn the router on, it runs through the following boot process. The Power-On Self Test (POST) checks the router’s hardware. When the POST completes successfully, the System OK LED indicator comes on.

The router checks the configuration register to identify where to load the IOS image from. A setting of 0×2102 means that the router will use information in the startup-config file to locate the IOS image. If the startup-config file is missing or does not specify a location, it will check the following locations for the IOS image:

1. Flash (the default location)

2. TFTP server

3. ROM (used if no other source is found)

The router loads the configuration file into RAM (which configures the router). The router can load a configuration file from:

+ NVRAM (startup-configuration file)

+ TFTP server

If a configuration file is not found, the router starts in setup mode.

Okay, in this micro post one more thing, we need to see is what can “show version” command tells us about CISCO IOS:

Software Version	- IOS software version (stored in flash)
Bootstrap Version	- Bootstrap version (stored in Boot ROM)
System up-time	- Time since last reboot
System restart info	- Method of restart (e.g. power cycle, crash)
Software image name	- IOS filename stored in flash
Router Type and Processor type	- Model number and processor type
Memory type and allocation (Shared/Main)	- Main Processor RAM - Shared Packet I/O buffering
Software Features	- Supported protocols / feature sets
Hardware Interfaces	- Interfaces available on router
Configuration Register	- Bootup specifications, console speed setting, etc.

The following is a sample output of a show version command.

Router# show version

Cisco Internetwork Operating System Software

IOS (tm) 3600 Software (C3640-J-M), Version 11.2(6)P, SHARED PLATFORM,

RELEASE SOFTWARE (fc1)

Compiled Mon 12-May-97 15:07 by tej

Image text-base: 0x600088A0, data-base: 0x6075C000

ROM: System Bootstrap, Version 11.1(7)AX [kuong (7)AX], EARLY DEPLOYMENT

RELEASE SOFTWARE (fc2)

Router uptime is 1 week, 1 day, 38 minutes

System restarted by power-on

System image file is "flash:c3640-j-mz_112-6_P.bin", booted

via flash

Host configuration file is "3600_4-confg", booted via tftp

from 171.69.83.194

cisco 3640 (R4700) processor (revision 0x00) with 107520K/23552K bytes

of memory.

Processor board ID 03084730

R4700 processor, Implementation 33, Revision 1.0

Bridging software.

X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.

TN3270 Emulation software.

Primary Rate ISDN software, Version 1.0.

2 Ethernet/IEEE 802.3 interface(s)

97 Serial network interface(s)

4 Channelized T1/PRI port(s)

DRAM configuration is 64 bits wide with parity disabled.

125K bytes of non-volatile configuration memory.

16384K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102

Commands execution hierarchy on IOS is like :

some other interesting commands worth knowing on a CISCO IOS are :

R1#show file systems
File Systems:

Size(b) Free(b) Type Flags Prefixes
- - opaque rw archive:
- - opaque rw system:
57336 57051 nvram rw nvram:
- - opaque rw null:
- - network rw tftp:
* 16777212 16777212 flash rw flash:
- - flash rw slot0:
- - opaque wo syslog:
- - opaque rw xmodem:
- - opaque rw ymodem:
- - network rw rcp:
- - network rw pram:
- - network rw ftp:
- - network rw http:
- - network rw scp:
- - network rw https:
- - opaque ro cns:

R1#show inventory
NAME: "2691 chassis", DESCR: "2691 chassis"
PID: , VID: 0.1, SN: XXXXXXXXXXX

R1#show diag
2691 Backplane EEPROM:
PCB Serial Number : XXXXXXXXXXX
Processor type : 66
Top Assy. Part Number : 800-09616-02
Board Revision : F0
Fab Part Number : 28-4226-06
Deviation Number : 65535-65535
Manufacturing Test Data : FF FF FF FF FF FF FF FF
RMA Number : 255-255-255-255
RMA Test History : FF
RMA History : FF
Chassis Serial Number : XXXXXXXXXXX
Chassis MAC Address : c000.1310.0000
MAC Address block size : 32
Field Diagnostics Data : FF FF FF FF FF FF FF FF
Hardware Revision : 0.1
Number of Slots : 1
EEPROM format version 4
EEPROM contents (hex):
0x00: 04 FF C1 8B 58 58 58 58 58 58 58 58 58 58 58 09
0x10: 66 40 02 58 C0 46 03 20 00 25 90 02 42 46 30 85
0x20: 1C 10 82 06 80 FF FF FF FF C4 08 FF FF FF FF FF
0x30: FF FF FF 81 FF FF FF FF 03 FF 04 FF C2 8B 58 58
0x40: 58 58 58 58 58 58 58 58 58 C3 06 C0 00 13 10 00
0x50: 00 43 00 20 C5 08 FF FF FF FF FF FF FF FF 41 00
0x60: 01 01 01 FF FF FF FF FF FF FF FF FF FF FF FF FF
0x70: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
Slot 0:
C2691 Mother board 2FE(TX)-3W Port adapter, 2 ports
Port adapter is analyzed
Port adapter insertion time unknown
EEPROM contents at hardware discovery:
PCB Serial Number : XXXXXXXXXXX
Processor type : 66
Top Assy. Part Number : 800-09616-02
Board Revision : F0
Fab Part Number : 28-4226-06
Deviation Number : 65535-65535
Manufacturing Test Data : FF FF FF FF FF FF FF FF
RMA Number : 255-255-255-255
RMA Test History : FF
RMA History : FF
Chassis Serial Number : XXXXXXXXXXX
Chassis MAC Address : c000.1310.0000
MAC Address block size : 32
Field Diagnostics Data : FF FF FF FF FF FF FF FF
Hardware Revision : 0.1
Number of Slots : 1
Product (FRU) Number : C2691-2FE
EEPROM format version 4
EEPROM contents (hex):
0x00: 04 FF C1 8B 58 58 58 58 58 58 58 58 58 58 58 09
0x10: 66 40 02 58 C0 46 03 20 00 25 90 02 42 46 30 85
0x20: 1C 10 82 06 80 FF FF FF FF C4 08 FF FF FF FF FF
0x30: FF FF FF 81 FF FF FF FF 03 FF 04 FF C2 8B 58 58
0x40: 58 58 58 58 58 58 58 58 58 C3 06 C0 00 13 10 00
0x50: 00 43 00 20 C5 08 FF FF FF FF FF FF FF FF 41 00
0x60: 01 01 01 FF FF FF FF FF FF FF FF FF FF FF FF FF
0x70: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF

One other things, mostly a CCNA student like me is confuse. Its the value of config register. The simple philosophy behind it is if config register value is 0x2102, router will look for configuration in NVRAM:

R1#show version | include register

Configuration register is 0x2102

If we change the config register valure form global configuration to 0x2142, any configuration in NVRAM will be ignored if a router is rebooted and it will enter into initial configuration mode. Please reread the last sentence multiple times to solidify the concept.

(Please note, i will keep on updating this post to add more fresh information into it, so you dont need to studty different dumps again and again :) Please leave your comments and suggestion, it would really help me to learn more and more)

My CISCO Journal

All things about CISCO IOS

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