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http:\\ciscocertifications.info
Transmission is resumed when the receiving device sends a packet with a window size higher than
zero.
*Keypoints:Data arriving faster than the device can handle are stored in memory.Flow control is maintained by the receiving device sending Receive ready/not ready messages tothe transmitting device.Know that a zero window size means to stop transmitting packets.If a sending device does not receive any acknowledgement at all, it will retransmit the last pack-ets at a reduce rate.Positive acknowledgement requires a recipient to communicate with the sending device by re-turning an acknowledgement.CISCO IOS
The CISCO Internetwork Operating System (IOS) is the operating system software that comes with all
CISCO routers.
IOS Router Modes
The IOS interface provides for 6 basic modes of operation.
MODEDescriptionAccessCommand Prompt
User EXEC Mode
Provides for limited examination
of router information.
Default mode
at login
Router>
Privileged EXEC
Mode
Provides detailed examination,
testing, debugging and file ma-
nipulation
Type enable at
command
prompt
Router#
Global Configuration
Mode
Allows you to change high level
router configuration
Type config t
at Priv mode
prompt
Router(config)#
ROM Monitor Mode
Automatic if the IOS does not
exist or the boot sequence is
interrupted
N/A
> or rommon>
Setup Mode
Prompted dialog that helps you
setup router configuration
Type setup at
Priv mode
prompt
Will display a series ofquestions.
RXBoot Mode
Helper software that helps the
router boot when it cannot find
the IOS image in FLASH
N/A
Router<boot>Global Configuration Mode
The Global configuration mode also allows you access to more specific router configuration modes.
The 2 primary ones you should know about are the Interface and Subinterface modes.
Router(config-if)# - The Interface configuration mode is entered by typing the word Interface at the
Global configuration prompt.
Router(config)# interface <interface type and number>
Router(config-subif)# - is a variation on the Interface command and can be access as shown below.
This lets you divide any interface into smaller virtual interfaces.
Router(config)# interface <interface type and number>.<subinterface-number>Logging in
When you first log into a router you are prompted with: