Cisco ROMMON Privilege Mode - Fixing a broken cookie.

This blog will be about ROMMON Mode on a Cisco ISR and some of the issue's that I had when I started up one of my 2800's at home. It seems that the cookie was corrupt and the router would not boot because it thought I had the incorrect image on the flash which was not the case.

So after doing a lot of searching I found out that I needed to fix the cookie and enter privilege mode of ROMMON to do this. I have been working with Cisco hardware for quite sometime and had never once heard of this little known TAC feature.

Ok, now onto the good stuff.

DISCLAIMER: USE AT YOUR OWN RISK | USE AT YOUR OWN RISK | USE AT YOUR OWN RISK

Here is the error that I was getting when I was trying to boot up my router.

"Readonly ROMMON initialized
loadprog: error - Invalid image for platform"

Now to enter the privledge mode of ROMMON. You will need to find the password to get
in and to get this password, you will need to display the cookie in ROMMON and find
a site that can decipher it for you.

This is the website that I found and kudos to this person!!

http://ers.pp.ru/cgi-bin/priv.cgi

Here is a partial piece of the cookie that was on my router:

rommon 2 > cookie

cookie:
04 ff 09 86 ff ff ff ff ff ff ff ff ff ff ff ff
4f 43 31 31 31 37 33 38 46 50 40 04 0c 41 07 00
82 49 1f fe 07 42 41 30 c0 46 03 20 00 5b 8b 05
88 00 00 00 00 02 04 c6 8a 49 50 4d 37 56 30 30

Now once that you have this on your screen, go to the website mentioned above and
paste the entire first line into the box. It will be a 4 digit password that it
spits out.

Now that you have your password, type in: priv and hit enter, input your password
and the outpur will be something like this.

rommon 7 > priv
Password:
You now have access to the full set of monitor commands.
Warning: some commands will allow you to destroy your
configuration and/or system images and could render
the machine unbootable.

Now that you are here, you will need to fix your cookie and will be a topic for
another blog post but what I did was boot up another router into ROMMON and grabbed
the cookie off of that one. (Thats probably not the best idea as it seems that the
MAC address' for the interfaces are derived from this Hexa-Decimal cookie.)

rommon 8 > ?
addrloop            walk 1 thru range of addresses
alias               set and display aliases command
alter               alter locations in memory
berrscan            scan range of addresses for bus errors
boot                boot up an external process
break               set/show/clear the breakpoint
call                call a subroutine at address with converted hex args
cat                 concatenate files
checksum            checksum a block of memory
clrerr              clear the error log
compare             compare two blocks of memory
confreg             configuration register utility
cont                continue executing a downloaded image
context             display the context of a loaded image
cookie              display contents of motherboard cookie PROM in hex
cpu                 cpu / system information and control
cycles              excercise the hardware with all possible cycles
dev                 list the device table
dir                 list files in file system
dis                 disassemble instruction stream
dnld                serial download a program module
dram                verify DRAM
dump                display a block of memory
echo                monitor echo command
errlog              display the error log
fdump               file dump utility
fill                fill a block of memory
flash               flash services command
frame               print out a selected stack frame
giodn               gio ucode download
giopref             select which gio to boot next
gioshow             show the gio version
gt96100             print out GT96100 registers
gt96100fe           print out GT96100 FE registers
help                monitor builtin command help
history             monitor command history
ifill               fill a block of memory w/incrementing pattern
iomemset            set IO memory percent
initfs              re-initialize the file system access structures
jump                call a subroutine at address with argc/argv
launch              launch a downloaded image
leds                check out the error LED
memdebug            write/read/verify scope loop
meminfo             main memory information
memloop             write or read scope loop
memtest             simple memory test
menu                main diagnostic menu
move                move a block of memory
repeat              repeat a monitor command
reset               system reset
rommon-pref         Select ROMMON
set                 display the monitor variables
showmon             display currently selected ROM monitor
sleep               millisecond sleep command
speed               timed performance loop
stack               produce a stack trace
sync                write monitor environment to NVRAM
sysret              print out info from last system return
tcal                timer calibration test
tftpdnld            tftp image download
tlbdump             display the cpu TLB
tlbflush            flush the TLB
tlbmap              initialize a TLB mapping
tlbpid              set/display process ID number
tlbphy              search TLB for physical translation
tlbtest             test the TLB
tlbscan             scan for TLB exceptions
tlbvir              search TLB for a virtual translation
tscope              timer scope loop
unalias             unset an alias
unset               unset a monitor variable
watchdog            test watchdog rebooting of the box
xmodem              x/ymodem image download

Now we need to enter cookie mode so type: cookie

This is what you will see:

View/alter bytes of serial cookie by field --
Input hex byte(s) or: CR -> skip field; ? -> list values

Now if you have a good cookie (In Hexa-Decimal), you will need to paste each line in one at a time.

bytes 0x08-0x0F: ff ff ff ff ff ff ff ff
               >
bytes 0x10-0x17: 4f 43 31 31 31 37 33 38
               >
bytes 0x18-0x1F: 46 50 40 04 0c 41 07 00
               >
bytes 0x20-0x27: 82 49 1f fe 07 42 41 30

<output omitted>

######################

Here are a few more show commands:

rommon 13 > menu

Main Diagnostic Menu
a: alter diag flags
b: basic utilities
c: do all diags in this menu
d: do group of diags in this menu
e: monitor image checksum test
f: internal interrupt test
g: bev state test
h: timer interrupt test
i: size main memory
j: main memory test
k: aux loopback test
l: aux port interrupt test
m: cookie test
n: primary data cache test
o: secondary data cache test
p: tlb test
q: mother board reg test
r: gt96xx dma test
x: return to previous menu
FLAGS: Continuous OFF  Stop on error OFF  Loop on error OFF  Quiet mode OFF

enter Main Diagnostic Menu item > m

*** Warning: if power is lost or user sends break ***
the system will not recover until cookie content is restored.

main board cookie test cookie out of scope, cookie number 0.
phase 1: cookie test with 0x5a5a pattern, main board cookie test
*** TLB (Load/Fetch) Exception ***
Access address = 0x10
PC = 0xbfc1efe8, Cause = 0x8, Status Reg = 0x3041e803

enter Main Diagnostic Menu item > b

Diagnostic Utilities Menu
a: alter memory
b: compare memory block
c: display memory
d: move memory block
e: fill memory
f: memory test
g: memory read or write loop
h: memory debug loop
i: address loop
j: system reset
k: system cold
l: console break interrupt test
m: AUX port echo test
n: show mother board regs
o: poll slots
p: mother board cookie utility
q: show GT96K registers
r: show NM PCI regs
s: PCI config write
t: PCI config read
u: show CF info
x: return to previous menu

Now if you have done everything correct, type the (3) commands below and it should boot up just fine.

rommon 8 > initfs
rommon 9 > sync
rommon 10 > reset

System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 2006 by cisco Systems, Inc.
PLD version 0x10
GIO ASIC version 0x127
c2801 platform with 262144 Kbytes of main memory
Main memory is configured to 64 bit mode with parity disabled


Readonly ROMMON initialized
program load complete, entry point: 0x8000f000, size: 0xcb80
program load complete, entry point: 0x8000f000, size: 0xcb80

program load complete, entry point: 0x8000f000, size: 0x2fb6af8
Self decompressing the image :
####################################################################################
####################################################################################
####################################################################################
############# [OK]

Smart Init is enabled
smart init is sizing iomem
  ID            MEMORY_REQ         TYPE
                0X003AA110 public buffer pools
                0X00211000 public particle pools
                0X00020000 Crypto module pools
                0X00120000 VPM buffer pools
0X0012          0X00035000 Card in slot 1
                0X000021B8 Onboard USB

If any of the above Memory Requirements are
"UNKNOWN", you may be using an unsupported
configuration or there is a software problem and
system operation may be compromised.

Allocating additional 12389767 bytes to IO Memory.
PMem allocated: 245366784 bytes; IOMem allocated: 23068672 bytes

Cisco IOS Software, 2801 Software (C2801-ADVENTERPRISEK9-M), Version 12.4(22)YB6,
RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Wed 02-Jun-10 22:33 by prod_rel_team

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:
http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to
export@cisco.com.

Installed image archive
Cisco 2801 (revision 6.0) with 239616K/22528K bytes of memory.
Processor board ID FTX1023Y0S3
2 FastEthernet interfaces
2 Serial(sync/async) interfaces
1 Virtual Private Network (VPN) Module
DRAM configuration is 64 bits wide with parity disabled.
191K bytes of NVRAM.
63984K bytes of USB Flash usbflash0 (Read/Write)
125440K bytes of ATA CompactFlash (Read/Write)