CIDR

• Classless Inter-Domain Routing
• Used in
• Security groups
• AWS networking
• Help define IP Range
• Has two components
• Base IP (XX.XX.XX.XX)
  • IP that contains in the range
• Subnet Mask (/XX)
  • Determine how many bits can be change in the IP

Subnet Mask

• Calculate IP Ranges
• Formula (2^(32-subnetMaskNumber))
• Some Examples
  • /32 allows 1 IP = 2^0
  • /31 allows 2 IP = 2^1
  • /30 allows 4 IP = 2^2
  • /29 allows 8 IP = 2^3
  • /28 allows 16 IP = 2^4
  • /27 allows 32 IP = 2^5
  • /26 allows 64 IP = 2^6
  • /25 allows 128 IP = 2^7
  • /24 allows 256 IP = 2^8
  • /16 allows 65,536 IP = 2^16
  • /0 allows ALL IP = 2^32
• Quick Memo
  • /32 - no IP number can change
  • /24 - last IP number can change
  • /16 - last IP two numbers can change
  • /8 - last IP three numbers can change
  • /0 - All IP numbers can change
• Exercise
  • Find range 192.168.0.0/24
  • Last IP number can change
  • Range be 192.168.0.0 to 192.168.0.255 (256 IP)
  • Alternate 2^(32-24) = 256 IP
  • Find range 192.168.0.0/16
  • Last 2 IP number can change
  • Range be 192.168.0.0 to 192.168.255.255 (65,536 IP)
  • Alternate 2^(32-16) = 65,536 IP
  • Find range 134.56.78.123/32
  • No number can change
  • Range be 134.56.78.123 to 134.56.78.123 (1 IP)
  • Alternate 2^(32-32) = 1 IP
  • Find range 0.0.0.0/32
  • All number can change
  • Range be 0.0.0.0 to 255.255.255.255 (ALL IP)
  • Alternate 2^(32-0) = 2^32 IP = ALL IP

Private IP

• Big Network Range 10.0.0.0 - 10.255.255.255 and CIDR (10.0.0.0/8)
• AWS Default Range 172.16.0.0 - 172.31.255.255 and CIDR (172.16.0.0/12)
• Home Network Range 192.168.0.0 - 192.168.255.255 and CIDR (192.168.0.0/16)

Public IP

• Any IP but Private IP