06 Hexadecimal

25. Hexadecimal - why do we care?

• Why hexadecimals are important?
  • MAC Addresses are written in hexadecimal
  • IPv6 is written in hexadecimal
• What is physical address?
  • Physical address or in other words mac address

26. Hexadecimal - Lab demonstration

[[MAC Address]] is 48bit number.

• 12 hexadecimal values x 4 bit each = 48 bits
  • 1st half of MAC address is usually manufacturers organizationally unique identifier (OUI).
  • 2nd half is unique number.
• MAC addresses are usually written in one of the following formats:
  • MMMM-MMSS-SSSS
  • MM:MM:MM:SS:SS:SS
• [[ARP]] (Address Resolution Protocol) is used to find MAC address of another device in the network.
  • ARP cache / ARP table maintains all the mapping between IP of the device and the MAC address.
  • To identify the devices, we need to ping the destination device first
  • Then its MAC address will show with arp -a
  • show mac address-table - command to see Mac Addresses learned by the switch

27. Hexadecimal calculations (16:05)

Decimal is a Base 10 numbering system which uses 10 numbers

• 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Binary is Base 2 numbering system which uses 2 numbers:

• 0, 1

Hexadecimal is Base 16 which uses 16 numbers:

• 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
  • A -> 10
  • B -> 11
  • C -> 12
  • D -> 13
  • E -> 14
  • F -> 15

To convert Decimal into HEX:

1. Convert Decimal into Binary
   133 = 1000 0101
2. Then convert each group into 1 Digit of HEX
   1000 0101 1000 = 8+0+0+0 = 8 = 8 0101 = 0+4+0+1 = 5 = 5
   HEX = 85

To convert Binary to HEX:

1. Split Binary Output of 8 bits into groups of 4 bits
2. Then convert each group into 1 Digit of HEX

Convert HEX to Decimal

1. Split HEX into 2 digits
   F8
   F 8

2. Convert each digit into Binary
   F = 15 = 8+4+2+1=1111
   8 = 8 = 8+0+0+0=1000

3. Convert binary into decimal
   1111 1000 = 128+64+32+16+8 = ==248==

27.1 Quiz 2

• What is the decimal equivalent of hexadecimal E1?
  • E = 14 = 8+4+2+0= 1110
  • 1 = 1 = 0001
  • 1110 0001 = 128 + 64 + 32 + 1 = 225
  • 225
• What is the hexadecimal  equivalent of decimal 199?
  • 199 = 128 + 64 = 192 + 4 + 2 + 1 = 1100 0111
  • 1100 = 8+4+0+0= 12 = C
  • 0111 = 4+2+1=7
  • C7
• What is the hexadecimal equivalent of decimal 229?
  • 229 = 128+64+32=224+0+0+4+0+1=11100101
  • 1110 = 14 = E
  • 0101= 5
  • E5
• What is the decimal equivalent of hexadecimal E9?
  • E = 14 = 8+4+2+0= 1110
  • 9 = 8+0+0+1 = 1001
  • 1110 1001 = 128+64+32+0+8+0+0+1 = 233
• What is the hexadecimal equivalent of 10.1.12.123?
  • 10 = A -> 0A
  • 1 = 1 -> 01
  • 12 = C -> 0C
  • 123 = 0+64+32=96+16=112+8=220+0+2+1= 01111011
    • 0111= 7
    • 1011=11
    • 7B
• What is the decimal equivalent of hexadecimal AB?
  • A = 10 -> 1010
  • B = 11 -> 1011
  • 1011 1011 -> 128+0+32+16+8+0+2+1=171
  • 171
• What is the hexadecimal equivalent of 12.254.234.133?
  • 12 -> C -> 0C
  • 254 -> 1111 1110 -> FE
  • 234 -> 1110 1010 -> EA
  • 133 -> 1000 0101 -> 85

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Flashcards/Active Recall Q+A:

Why hexadecimals are important? #card

• MAC Addresses are written in hexadecimal
• IPv6 is written in hexadecimal

What is physical address? #card

• Physical address or in other words [[mac address]]

How many bit is [[MAC Address]]? #card

• [[MAC Address]] is 48bit long = 12 hexadecimal values x 4bit each.
• MMMM-MMSS-SSSS e.g. 0050-56C0-0008
• 0000 0000 -> 00
• 01010000 -> 50
• 01010110 -> 56
• 11000000 -> C0
• 00000000 -> 00
• 00001000 -> 08

What is [[MAC Address]] ? #card

• 12 hexadecimal values x 4 bit each = 48 bits
• 1st half of MAC address is usually manufacturers organizationally unique identifier (OUI).
• 2nd half is unique number.
• MAC addresses are usually written in one of the following formats:
• MMMM-MMSS-SSSS
• MM:MM:MM:SS:SS:SS

What is [[ARP]]? #card

• ARP(Address Resolution Protocol) is used to find MAC Addresses of other devices in the network.

What is [[ARP cache]]? #card

• ARP cache contains all the entries that map IP Addresses to MAC addresses.
• ARP cache can contain dynamic (learned) entries and static (user-configures) entries. The software places a dynamic entry in the ARP cache when it learns a devices MAC address from ARP request or ARP reply from the device. e.g. after `ping` 'ing the destination device.

How to view [[ARP cache]] ? #card

• `arp -a`
• `show mac address-table` - command to see Mac Addresses learned by the switch

What are [[Base 2]], [[Base 10]], [[Base 16]] numbering systems? #card

• Base 2 consists of 2 numbers 0 or 1. It is Binary.
• Base 10 consists of 10 numbers 0, 1,2,3,4,5,6,7,8,9 -> Decimal
• Base 16 consists of 16 numbers -> hexadecimal
• 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
• A -> 10
• B -> 11
• C -> 12
• D -> 13
• E -> 14
• F -> 15

How to convert Decimal into HEX? #card

1. Convert Decimal into Binary
   133 = 1000 0101
2. Then convert each group into 1 Digit of HEX
   1000 0101
   1000 = 8+0+0+0 = 8 = 8
   0101 = 0+4+0+1 = 5 = 5
   HEX = 85
   

How to convert HEX to Decimal? #card

1. Split HEX into 2 digits
   F8
   F 8
   
2. Convert each digit into Binary
   F = 15 = 8+4+2+1=1111
   = 8 = 8+0+0+0=1000
   
3. Convert binary into decimal
   1000 = 128+64+32+16+8 = 248
   

What is the decimal equivalent of hexadecimal E1? #card

• E = 14 = 8+4+2+0= 1110
• 1 = 1 = 0001
• 1110 0001 = 128 + 64 + 32 + 1 = 225
• 225

What is the hexadecimal  equivalent of decimal 199? #card

• 199 = 128 + 64 = 192 + 4 + 2 + 1 = 1100 0111
• 1100 = 8+4+0+0= 12 = C
• 0111 = 4+2+1=*7*
• C7

What is the decimal equivalent of hexadecimal AB? #card

• A = 10 -> 1010
• B = 11 -> 1011
• 1011 1011 -> 128+0+32+16+8+0+2+1=171
• 171

One Page Summary

MAC address, ARP, ARP cache, Binary, Decimal, Hexadecimal.