CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Cisco IOS treats a mistyped command as a hostname and will try to resolve it using DNS.
DNS resolution is a time consuming process and is enabled by default, but DNS server is rarely
deployed in lab environments. The no ip domain-lookup global configuration command
disables this default feature.
- The erase startup-config and erase nvram: privileged commands can be used to erase the
startup-config in the NVRAM, which cause a Cisco router or switch to perform factory reset and
enter into the initial configuration dialog upon next reboot.
- The reload [at hh:mm day month | in reload-delay] [reason] privileged command warm
boot a Cisco device. The reload cancel privileged command cancels a scheduled reboot.
- Below lists the types of memory that can be found in Cisco devices:
RAM Used as working storage for packet buffers, ARP cache, routing tables, etc.
The running-config is being stored here.
ROM Normally stores a limited-function bootable IOS image – bootstrap code,
which is not intended for normal operation and is loaded after the POST to
locate and load the full IOS image or ROMmon (the bootstrap code itself)
by examining the configuration register.
Flash memory Either an Intel EEPROM or a PCMCIA card. It is an erasable, rewriteable
and permanent storage. It stores fully functional IOS images and is the
default location where a device obtains its IOS at boot time. It can be used to
store any other files as well (some routers can store configuration files here).
The show flash: privileged command can be used to view the contents of
the Flash memory.
NVRAM Nonvolatile RAM that stores the startup-config.
EEPROM – Electronically Erasable Programmable Read-Only Memory.
- The copy {source-file} {destination-file} privileged command is used to copy files. It is
mainly used to duplicate configuration files as well as backup and upgrade of IOS images.
copy running-config startup-config
RAM NVRAM
copy startup-config running-config
(merge)
copy running-config tftp
copy startup-config tftp
copy tftp startup-config
copy tftp running-config (merge)
Figure 4-1: The IOS Copy Operations
TFTP
- During the IOS upgrade process, the device will try to obtain the following information:
i) The IP address of the TFTP server.
ii) The name of the IOS image file.
iii) Does the Flash memory have available space for the file?
iv) Does the TFTP server actually have the specified file?
v) Does it need to erase or delete the old IOS image?
- The TFTP server can either resides on the same subnet with an interface; or a remote subnet
(requires the default route configuration).
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com