5.5.10 IPv6

• Support billions of hosts - uses 16 byte (128 bit) addresses so theoretically 340,282,366,920,938,463,463,374,607,431,768,211,456 host addresses.
• Addresses written using colon hexadecimal notation (e.g. 8000:0000:0000:0000:0123:5678:CDEF)
• Zero compression in address representation replaces sequences of zeros with two colons. For example, the 32 bit IPv4 addresses start with 96 bits of 0, could be written as ::192.31.20.46
• Reduce size of routing tables - 16 byte addresses allow deeper hierarchy.
• Simplify protocol so routers can process packets faster
  • header reduced to 7 fields from 13 in IPv4
  • Removed checksum field since transport and data link protocols normally have own and network communication highly reliable.
• Provide better security
  • supports state-of-the-art checksum authentication and user optional encoding algorithm for privacy
  • Encryption is essentially an end-to-end issue.
• Attention to type of service, particularly real-time data - Priority field defining slow and fast data.
• Aid multicasting by allowing scopes to be defined - Multicast addresses with 4-bit scope field and 112-bit group field.
• Support roaming hosts - not supported directly, still possible via foreign/home agents
• Allow protocol to evolve - Much of IPv4 header pushed into higher level, end-to-end protocols (e.g. checksum) which can be implemented independent of routing issues.
• Permit old and new protocols to coexist
  • not compatible with IPv4
  • is compatible with TCP, UDP, ICMP, DNS, etc. except for larger addresses.
  • Initially islands of IPv6 tunnel through IPv4 networks until eventually merge into a complete IPv6 network.
  • Current investment in IPv4 routers too large to change immediately.

IPv4 header

IPv6 header

The general form of an IPv6 datagram. Extension headers are optional - the minimum datagram has a base header followed by data.

IPv6 base header

• VERS - Identifies as protocol 6.
• TRAFFIC CLASS - Specifies general characteristics required by datagram. Real time audio (voice over IP) might request path with less than 100 ms delay.
• FLOW LABEL - Used by applications that require performance guarantees, can be used to identify a specific path through network. After path established, an ID is returned that sender places in this field.
• PAYLOAD LENGTH - is what it says.
• HOP LIMIT - Byte means 255 limit.
• SOURCE and DESTINATION ADDRESS - 16 byte addresses, (e.g. 8000:0000:0000:0000:0123:5678:CDEF).
• NEXT HEADER - Specifies type of information that follows the current header; can be the type of an extension header or type of data in payload. The following shows a) NEXT=TCP to be TCP data and b) NEXT=ROUTE to be a route header which contains NEXT=TCP.