IPv6 is the “next generation” protocol designed by the IETF to replace the current version Internet Protocol, IP Version 4 (IPv4).
Many of today’s Internet and our enterprise networks use IPv4, which is now more than 20 years old. IPv4 was a big success in networking world. In the seventies, when IPv4 was developed, the current size of the Internet was beyond thoughts. It is extraordinary, that this protocol is still able to be the ship for the Internet. But it hits the boundary since quite some time. The most understandable limitation is the address space which is short and running out soon. We have facilitated ourselves by using technologies like NAT, but this is not a long term resolution. By using the IPv6 address space of 128 bits (compared to 32 bits with IPv4), the boundary on addresses has been extended from a theoretical 4 billion to 340 trillion (3.4 x 10^38) – 2^32 compared to 2^128.
Motivation Towards IPv6
Limited address space is not the only motive to move toward IPv6. The inventors of IPv6 have become skilled from the many years of using IPv4. They reserved all the strong points from IPv4 and appended a lot of functionality which will be required in our prospect networks. Especially the advanced auto configuration characteristics will allow businesses to install a great array of new desktop, mobile and embedded network devices in a cost effective, controlled manner. Interesting Mobility improvements will present the foundation for new types of services that are build up these days.
Enhancement in IPv4
IPv6 also adds several enhancements to IPv4 in areas such as security, mobility, QOS, scalability of the network architecture and routing. IPv6 is therefore very much suited for scalable and converged networks. A number of transition and coexistence mechanisms have been developed and are steadyly improved in order to build the transition a smooth one. It is anticipated that IPv6 will gradually replace IPv4 in some years, with the two protocols coexisting for many years during a transition period.
Unlike the “old” IPv4 notation, IPv6 addresses are typed in hex format and look like this: 2001:08e0:7d83:7d86:4f81:4c72:1d81 or something like 2001:08e0::1.
We have different types of IPv6 addresses:
- Unicast: Assigned to a single interface. One-to-one delivery to single interface,
- Multicast: Assigned to a set of interfaces. One-to-many delivery to all interfaces in the set,
- Anycast: One-to-one-of-many delivery to a single interface in the set that is closest.
There are no more broadcast addresses.
IPv6 unicast address can be aggregated with prefixes of arbitrary bit-length similar to IPv4 addresses under CIDR.
There are a number of types/scopes of unicast addresses in IPv6, in particular global unicast, site-local unicast, and link-local unicast.
Global Unicast Addresses
- Routable on Internet
- Structured as a hierarchy to keep the aggregation
Unique-Local Addresses :
- Local communications
- Inter-site VPNs
- Not routable on the Internet
Link-Local Addresses :
- Address for Communication between two IPv6 device (like ARP but at Layer 3)
- Automatically assigned by Router as soon as IPv6 is enabled
- Also used for Next-Hop calculation in Routing Protocols
- Only Link Specific scope
- Remaining 54 bits could be Zero or any manual configured value
Interface identifiers in IPv6 unicast addresses are used to recognize interfaces on link. They are required to be exclusive on that link. Interface IDs are required to be 64 bits long.
The new IPv6 header is simpler than the IPv4 header.
The IPv6 header has 40 bytes instead of 20 bytes as in IPv4. In fact, half of the previous IPv4 header fields are eliminated. This enables much simpler processing of the packets, enhancing the performance and the routing effectiveness.
All fields are aligned to 64 bits, which enables direct storage and access in memory by fast lookups.
Checksum Removed Header of IPv6
The IPv6 header is also simpler due to the removal of the checksum. Not only is the space in the header reused, but more importantly, no recalculation is done by the routers in the path. This also provides routing efficiency. However, this doesn’t mean error detection is not handled – in most link layer technologies error detection is handled. In IPv4, TCP checksums are available and, optionally, UDP checksums. In IPv6, checksums are required for both transport protocols.
A new field is added to the IP header. The new flow label field enables per-flow processing by the routers during the path. This offers differentiation of the traffic at the IP layer without the requirement to perform other functions to identify the flows. With this label, a router need not open the transport inner packet to identify the flow, because it finds the information in the IP packet header itself.
For further details on IPv6 address format, Internet Protocol, Version 6 (IPv6) Specification (RFC 2460
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