IPv6

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Header

p17
V TC FL PL NH HL SA DA
Name Size Description
Version 4 bits Protocol Version, fixed to value 6
Traffic Class 8 bits Data priorities, realtime traffic, equals TOS in IPv4
Flow Label 20 bits Efficiency bypass for option parsing. Packets with the same flow label must have the same options.
Payload Length 16 bits Length of data, including extension headers, excluding the IPv6 header
Next Header 8 bits Either type of next protocol (6 for TCP, 17 for UDP) or number of extension header (44 for fragmentation header)
Hop Limit 8 bits equals TTL in IPv4
Source Address 128 bits
Destination Address 128 bits Either address of destination device, or of next hop in case of presence of routing header.

Options Headers

p26
If node gets a packet with an unknown extension header, it must drop the packet and inform the sender by an ICMPv6 message (Parameter Problem). Extension headers are optional, but if present must be sent in the following sequence:
  1. IPv6 Header
  2. Hop-by-Hop Options Header
    Jumbo Payload Option (> 65K), Option Router Alert
  3. Destination Options Header
    Options for routing target
  4. Routing Header
    Defines next hops which must be passed
  5. Fragment Header
  6. Authenticating Header
  7. Encapsulating Security Payload Header
  8. Destination Options Header
    Options for final target
  9. Upper-Layer Header (TCP, UDP, etc)
Fragmentation is done only by the sender (not by routers on the way, as in IPv4). Path MTU Discovery is used to determine the maximum packet size.

IPv6 Addresses

Global Routing Prefix (n bits) Subnet ID (64 - n bits) Interface ID (64 bits)

Links