hex, and big numbers...

65000 decimal equals FD-E8 in hex...

why?

65000 is a good number because:

http://www.bgp4.as/

A unique AS number (ASN) is allocated to each AS for use in BGP routing. The numbers are assigned by IANA and the Regional Internet Registries (RIR), the same authorities that allocate IP addresses. There are public numbers, which may be used on the Internet and range from 1 to 64511, and private numbers from 64512 to 65535, which can be used within an organization.

0 to 65535 is 65536 total numbers

and 2 to the 16th equals  65536

and 2 to the 15th equals 32768 which is a number dear to your heart...

and so on...  powers of 2 are not the enemy...
back to 65000...

in hex the rightmost place holder is units or 0-9 ABCDEF (10 - 15) comprising a total 16 numbers because hex is a base 16 number system...

to the left of the units place holder is the 16's place holder...

hex AC is 10*16 + 12*1 or 172...

to the left of the 16's place holder is the 16*16 place holder or 256...

and you love 256... you seeing a pattern here?

to the left of the 256 place holder is the 4096 place holder because 16 times 256 is 4096... every consecutive place holder to the left is again multiplied by 16...

so FD-E8 is...

time to break out the calculator:

F times 4096 + D times 256 + E times 16 + 1 times 8

 ta da...

you can applaud if you want to...

4096...

the significance of 4096 is understood in relation to switching, especially spanning tree...

what is 2 to the 12th?

4096... 

from: http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/spantree.html#wp1037363

A 12-bit extended system ID field is part of the bridge ID (see Table 28-1). Chassis that support only 64 MAC addresses always use the 12-bit extended system ID. On chassis that support 1024 MAC addresses, you can enable use of the extended system ID. STP uses the VLAN ID as the extended system ID.

When the extended system ID is enabled, the root bridge priority becomes a multiple of 4096 plus the VLAN ID. With the extended system ID enabled, a switch bridge ID (used by the spanning tree algorithm to determine the identity of the root bridge, the lowest being preferred) can only be specified as a multiple of 4096. Only the following values are possible: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, and 61440. 


then given this:

 Bridge Priority (2 bytes)—The priority or weight of a switch in relation to all other switches. The Priority field can have a value of 0 to 65,535 and defaults to 32,768 (or 0x8000) on every Catalyst switch.

so interpreting hex here from right to left, the first zero is the one's place holder, the second zero is the 16's place holder, the third zero is the 256's place holder and the 8 is the 4096's place holder...

8 times 4096 is 32768

0x1000 equals 4096

0x0100 equals 256

0x0010 equals 16

0x0000 equals ?

hex...

256 is the hundred's place holder

16 is the ten's place holder

1 is the one's place holder

256       16           1

hex 100 = what in decimal?

256 is the hundred's

16 is the ten's

1 is the one's

1                        0                        0

256                     0                        0

100 hex is 256 decimal

do you need a chart? what is 111 in hex?

256 16 1
1      1   1  equals 256 + 16 + 1 is 273 decimal

what is decimal cc? a is 10 b is 11 c is 12 d is 13 e is 14 f is 15

only 2 place holders here 10's and 1's

c in the ten's position is 12 (x16) +  c in the one's position is 12

12x16=192 + 12 = 204

check this calculator to see if it's correct...

http://easycalculation.com/hex-converter.php

see more in earlier posts...

http://insearchofthecert.blogspot.com/search/label/nibbles%20and%20bits

switchport identification...

use sh ver to find the mac address assigned to a switch...

sw2950_02#sh ver
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6K2L2Q4-M), Version 12.1(22)EA14, RELEASE SOFTWA

Processor board ID FHK0619X14J
Last reset from system-reset
Running Standard Image
24 FastEthernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address: 00:09:B7:3F:CE:80


so what is the mac of port 1?

sw2950_02#sh int fa0/1
FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0009.b73f.ce81 (bia 0009.b73f.ce81)

how about fa0/10? better know hex...

sw2950_02#sh int fa0/10
FastEthernet0/10 is down, line protocol is down (notconnect)
  Hardware is Fast Ethernet, address is 0009.b73f.ce8a (bia 0009.b73f.ce8a)

15 is easy...

sw2950_02#sh int fa0/15
FastEthernet0/15 is down, line protocol is down (notconnect)
  Hardware is Fast Ethernet, address is 0009.b73f.ce8f (bia 0009.b73f.ce8f)

16 is not...

sw2950_02#sh int fa0/16
FastEthernet0/16 is down, line protocol is down (notconnect)
  Hardware is Fast Ethernet, address is 0009.b73f.ce90 (bia 0009.b73f.ce90)

the ten's position incremented by one remainder zero is fa0/16...


which makes fa0/24 easy... what is 16 plus 8...

sw2950_02#sh int fa0/24
FastEthernet0/24 is down, line protocol is down (notconnect)
  Hardware is Fast Ethernet, address is 0009.b73f.ce98 (bia 0009.b73f.ce98)

bootstraps...

not sure if odom and the rest still mention this but booting or rebooting is derived from the idea of bootstraps, or more accurately, pulling oneself up by the bootstraps... the safest way to remember what configuration settings do is to look at the boot field...  the boot field is the last four bits (all the way to the right) that comprise a number in hex normally 0x2  or ox2102 which means to boot from the config file in flash if possible...

if the last number is 0 boot to rommon, if it's 1 boot software contained in rom...

0x2142 means bypass start (config in nvram) and is mostly used in password recovery...

use show version to see the current config-register setting, ie,

Configuration register is 0x2102 (will be 0x2142 at next reload)

show run and show start do NOT show the register setting but will show manually input boot system configuration...


r2620_01#sh run
Building configuration...

Current configuration : 2049 bytes
!
! Last configuration change at 12:51:27 UTC Sat Dec 17 2011
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname r2620_01
!
boot-start-marker
boot system tftp myass 255.255.255.255

my college friends and i used to refer to throwing up, as booting