Something I always forget, I can only remember 0x2102 and 0x2142 as both are the most used ones. Configuration register allows to set the boot mode of a IOS device. If we want to know which one we have configured, we do:

sh ver | i ion_reg Configuration register is 0x2102 router#

To configure it, in config mode:

config-register [new register]

Following all the possible values we have:

  • 0x102 : Ignores break, 9600 baud
  • 0x1202 : 1200 baud
  • 0x2101 : Boots into bootstrap, ignores break, boots into ROM if fails, 9600 baud
  • 0x2102 : Ignores break, boots into ROM if fails, 9600 baud. Is the default option for most platforms.
  • 0x2120 : Boots into ROM, 19200 baud
  • 0x2122 : Ignores break, boots into ROM if fails, 19200 baud
  • 0x2124 : Netboot, ignores break, boots into ROM if fails, 19200 baud
  • 0x2142 : Ignores break, boots into ROM if fails, 4800 baud
  • 0x2922 : Ignores break, boots into ROM if fails,, 38400 baud
  • 0x3122 : Ignores break, boots into ROM if fails, 57600 baud
  • 0x3902 : Ignores break, boots into ROM if fails, 115200 baud

Cheers,