Generally to upgrade/downgrade an IOS, you use the classical ftp/tftp transfer from a laptop to a router/switch; unfortunately, there are some cases where this way is not possible, so the only solution is to use the console.
Suppose you have to upload an image of about 20Mb. On a 9600bps intereface, the time required to upload this image is about 35minutes (20000000/9600)! Oh my God!
Fortunately Cisco permit to change the console speed using the command “speed”.
By default the console interface works at 9600bps:
Ciscozine#sh line console 0 Tty Line Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int 0 0 CTY - - - - - 0 0 0/0 - Line 0, Location: "", Type: "" Length: 24 lines, Width: 80 columns Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits Status: Ready Capabilities: none Modem state: Ready Group codes: 0 Modem hardware state: noCTS DSR* DTR RTS TTY NUMBER 0 Receive Overrun = 0, Carrier Detect Loss = 0 Receive Clock Glitch = 0, Transmit Underrun = 0 CTS Loss = 0, Transmit Clock Glitch = 0 Outcount = 0 totalout = 92838 incount = 0 totalin = 0 Special Chars: Escape Hold Stop Start Disconnect Activation ^^x none - - none Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch 00:10:00 never none not set Idle Session Disconnect Warning never Login-sequence User Response 00:00:30 Autoselect Initial Wait not set Modem type is unknown. Session limit is not set. Time since activation: never Editing is enabled. History is enabled, history size is 20. DNS resolution in show commands is enabled Full user help is disabled Allowed input transports are none. Allowed output transports are telnet. Preferred transport is telnet. Shell: enabled Shell trace: off Ciscozine#
…but it is possible “improve” the baud rate. To increase it:
Ciscozine(config)#line console 0 Ciscozine(config-line)#speed 115200
Ciscozine#sh line console 0
Tty Line Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
0 0 CTY - - - - - 0 0 0/0 -
Line 0, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 115200/115200, no parity, 2 stopbits, 8 databits
Status: Ready
Capabilities: none
Modem state: Ready
Group codes: 0
Modem hardware state: noCTS DSR* DTR RTS
TTY NUMBER 0
Receive Overrun = 0, Carrier Detect Loss = 0
Receive Clock Glitch = 0, Transmit Underrun = 0
CTS Loss = 0, Transmit Clock Glitch = 0
Outcount = 0 totalout = 94534 incount = 0 totalin = 0
Special Chars: Escape Hold Stop Start Disconnect Activation
^^x none - - none
Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch
00:10:00 never none not set
Idle Session Disconnect Warning
never
Login-sequence User Response
00:00:30
Autoselect Initial Wait
not set
Modem type is unknown.
Session limit is not set.
Time since activation: never
Editing is enabled.
History is enabled, history size is 20.
DNS resolution in show commands is enabled
Full user help is disabled
Allowed input transports are none.
Allowed output transports are telnet.
Preferred transport is telnet.
Shell: enabled
Shell trace: off
No output characters are padded
No special data dispatching characters
Ciscozine#
Now, the previous file of 20Mb is transferred in less than 3 minutes (20000000/115200)!
Note: Obviously, when you change the console speed on your device you have to change the console speed in your terminal!
Another solution to change the console speed is during the boot fase. In fact, if you enter in ROMmon mode, you can change this value using the command “confreg”.
rommon 1 >confreg
Configuration Summary
enabled are:
break/abort has effect
console baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n [n]: y
enable "diagnostic mode"? y/n [n]:
enable "use net in IP bcast address"? y/n [n]:
enable "load rom after netboot fails"? y/n [n]:
enable "use all zero broadcast"? y/n [n]:
disable "break/abort has effect"? y/n [n]:
enable "ignore system config info"? y/n [n]:
change console baud rate? y/n [n]: y
enter rate: 0 = 9600, 1 = 4800, 2 = 1200, 3 = 2400
4 = 19200, 5 = 38400, 6 = 57600, 7 = 115200 [0]: 7
change the boot characteristics? y/n [n]:
Configuration Summary
enabled are:
break/abort has effect
console baud: 115200
boot: the ROM Monitor
do you wish to change the configuration? y/n [n]:
You must reset or power cycle for new config to take effect.
rommon 2 >
Note: Once the router boots up in ROMmon, you need to exit the current terminal session and start a new one at a data rate of 115200 bps.
And what can you do if you don’t know the console speed?
A solution would be to just try the eight possible console speeds above and see which one works. Another solution (for Cisco 2600 and 3600 Series Routers) would be to open up the box and move a jumper. Yes, you have understood, you can reset this value moving a jumper!
Jumper J3 on the motherboard of the Cisco 2600 and 3600 Series Routers controls the speed reset. The factory default position of the shunt shorts pins 2-3. When the shunt is moved to pins 1-2, the console is reset to 9600 baud on the next power cycle. The following figures show the location of the console reset jumper, labeled DUART_RST or BAUD_RST.
Cisco 3640 Motherboard Showing Console Baud Reset Jumper
Cisco 2600 Motherboard Showing Console Baud Reset Jumper
Remember: If you open your device, you lose the warranty.
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