IPv4 and IPv6 basics

TOC

Here is a memo of me trying to understand typical IP address usages on typical desktop systems.

IPv4 and IPv6 basics

• IPv4

  • 8 bit * 4 = 32 bit address space (2^32 addresses)
  • Loopback: IP block=127.0.0.0/8 (2^24 addresses) for localhost.
  • Multicast IPv4 address block = 224.0.0.0/4
    • mDNS: IP=224.0.0.251, UDP, port=5353
  • Link-local address: IP block=169.254.0.0/16 (2^16 addresses)
  • Private IPv4 network
    • 10.0.0.0/8 – 1 x Class A network with 2^24=16777216 addresses
    • 172.16.0.0/12 – 2**4=16 x Class B networks, each with 2^16=65536 addresses
    • 192.168.0.0/16 – 2**8=256 x Class C networks, each with 2^8=256 addresses

• IPv6

  • 16 bit * 8 = 128 bit address space (2^128 addresses)
  • Loopback: IP=::1 for localhost.
  • Multicast IPv6 address block = ff00::/8
    • mDNS: IP=ff02::fb, UDP, port=5353
  • Link-local address: IP block=fe80::/10 (high 10 bits are IANA global ID, mid 54 bits are 0, low 64 bits are interface ID)
  • Private IPv6 network
    • fc00::/7 – 2^16 bits for subnet ID x subnet with 2^64 addresses

For more, read zero-configuration networking.

My /etc/hosts on hostname goofy has:

127.0.0.1	localhost
127.0.1.1	goofy

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Corresponding binary, hexadecimal, and decimal numbers

• Notable even numbers
  • 0b00000000 = 0x00 = 0
  • 0b00010000 = 0x10 = 16
  • 0b00100000 = 0x20 = 32
  • 0b01000000 = 0x40 = 64
  • 0b10000000 = 0x80 = 128
  • 0b10101000 = 0xa8 = 168
  • 0b11000000 = 0xc0 = 192
  • 0b100000000 = 0x100 = 256
• Notable odd numbers (above even number -1)
  • 0b00001111 = 0x0f = 15
  • 0b00011111 = 0x1f = 31
  • 0b00111111 = 0x3f = 63
  • 0b01111111 = 0x7f = 127
  • 0b10100111 = 0xa7 = 167
  • 0b10111111 = 0xbf = 191
  • 0b11111111 = 0xff = 255
• Notable negative numbers
  • 0b11111100 = 0xfc = 252 = -4
  • 0b11111101 = 0xfd = 253 = -3
  • 0b11111110 = 0xfe = 254 = -2
  • 0b11111111 = 0xff = 255 = -1