xmodem...

i was getting tired by the last router upgrade from smi to emi...

but first a moment from our sponsor, the 3550 switch...
the default baud rate out of the box is 9600 for a console connection, however, did you know that this cannot be changed using the configuration register... 3560's either...  so i have what appears to be a baud rate incompatibility with my console connection because after setting the term to 9600, 8, none. 1, i get weird ascii creatures... that's a pain in the ass... hope i don't end up in rommon mode after next reload...

back to the ios upgrade... i delete the current ios in flash, copy run start, and reload the router...

shit...

after it came back it couldn't find an ios... flash was empty... i should have gone to bed... like i said, i was tired... it's been years since i've done an xmodem ios transfer... i set the baud rate on the router to 115200 and xmodemed away... 2 hours later i finally had an ios in flash again... duh...

here's the key...  don't be a hero and delete flash from the cli by hand... let copy tftp flash do it for you... it will prompt you to erase before loading the new ios, and you won't be sitting there all night watching exclamation points go across your damn screen because you bounced the router before you loaded the ios...

i am a dumbass...

nibbles and bits

nibbles and bits...

the configuration register of a router is represented by a hex number, or 0x... it is a sixteen
bit number read from left to right starting from 15, and ending with 0, sixteen numbers total...
cisco loves the number sixteen because it is difficult to add sixteens... quick what is 16 plus
forty eight? 128 plus 16? how many 16's in 192? 16 x 4 is 64 which goes into 192 3 times... 3 x
four is 12... what is 12 hex?

 1      2       3      4      5      6      7         8       9      10      11      12     13     14     15     16
  16    32     48    64    80    96   112    128     144   160    176    192   208   224   240   256

0x2102 means load start from nvram if found

15 14 13 12 11 10   9  8  7  6  5  4  3  2  1  0
 8   4   2   1  8   4   2  1  8  4  2  1  8  4  2  1

15 to 0 are place positions
each group of 4 bits is a nibble
count the nibbles and bits
don't look at me... i didn't make this shit up

0010 0001 0000 0010 = 0x2102

try to think of all three number systems at once.. here is a great site that groups all three...
http://easycalculation.com/decimal-converter.php

decimal 20
is 14 in hex because 16 goes into 20 once with a remainder of 4
the binary value is 0001 0100 because 16 + 4 is twenty:

128 64 32 16   8 4 2 1
 0    0   0   1    0 1 0 0

back to 192, the beginning of the class C range of private adresses
16 goes into 192 12 times
12 = C in hex so 192 = C0 hex
192 = 11000000 because 128 + 64 + 0 + 0 + 0 + 0 + 0 + 0 = one hundred and 92

remember 128 64 32 16 8 4 2 1
8 4 2 1 binary = 15 decimal = F hex

what is decimal 42 in hex? 2A
binary? 00101010
10 = A = 1010
sixteen goes into 42 twice remainder 10