IPv4 Review

IPv4 Header

  • Version: 4
  • IHL (Internet Header Length): length of the header in 32-bit increments. Value 5 = 5 lines x 32 bits
  • TOS (Type of Service): used to prioritize the IP packet (QoS)
  • Total Length: 65535 bytes
  • Identification, Flags & Fragment Offset. Control of fragmentation
  • Flags: Bit 0 is reserved. If bit 1 is set to 0, fragmentation is allowed. If set to 1, not allowed. If bit 2 is set to 0, then it is the last fragment. If 1, more fragments follow.
  • Time to Live: lifetime of the packet. Each router reduces the value by 1
  • Protocol: e.g. TCP, UDP, ICMP, etc.
  • Header Checksum: checksum. Rarely used.
  • Source / Destination: destination and source address

IPv4 & IPv6 Header Differences

The IPv4 header can be between 20-60 bytes in size. In IPv6 the header has a fixed size and can be extended with ‘Extension Header’:

The following header types must be supported by IPv6:

  1. Hop-By-Hop Option Header
  2. Destination Option Header
  3. Routing Header
  4. Fragment Header
  5. Authentication Header (AH)
  6. Encapsulation Security Payload (ESP)

Each header type has a unique ID: https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml

IPv6 Address Types [Wikipedia]

IPv6 Notation

IPv6 - Example 7d21**:006a:9417:7d0e:0000:0000:490f:**07b1

IPv6 - Shortened notation 7d21**:06a:9417:7d0e:****:490f:**7b1

Representation of an IPv4 address in IPv6 IPv4: 188.68.58.170 IPv6: 0.0.0.0.188.68.58.170 or ::188.68.58.170 or IPv4: 127.0.0.1 IPv6: 0.0.0.0.0.0.0.1 or ::1

Within a browser, the address can be accessed within square brackets:

IPv6 Prefix IPv6 addresses can be classified by a prefix. A list of possible prefixes can be found here: https://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xhtml

Example of a ‘Global Unicast’ address

IPv6 DNS & DHCP The details of the changes to DNS & DHCP are specified in the following standards:

  • DNS: RFC 3596
  • DHCP: RFC 3315