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
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- 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)
Copyright (c) 1986-1997
by cisco Systems, Inc.
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.
SuperLAT software
copyright 1990 by Meridian Technology Corp).
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)
