Some more technicalities of IPv6

IPv6 Address representation.

Where x is a 16-bit hexadecimal field.

Some more examples.


1) 2031:0000:130F:0000:0000:09C0:876A:130B


We can write this address in other alternate ways as well for example

a) 2031:0:130F:0:0:9C0:876A:130B

* The leading zeros in a field are optional, so that 09C0 = 9C0 and 0000 = 0.
* Successive fields of zero can be represented as : : (double colons) but only once per address.


b) 2031:0:130F::9C0876A:130B


* Using the double colon "::" notation greatly reduces the size of most addresses look at the following address.

2) FF01:0:0:0:0:0:0:1 --> FF01::1


* An unspecified address is written as "::" because it contains only zeros.
3) 0:0:0:0:0:0:0:0 --> ::


NOTE: For example for address FF01::1, An address parser identifies the number of missing zeros by separating the two parts and entering 0 until the 128 bits are completed. If two double colon notations are placed int the address then there is no way to identify the size of each block of zeros.

IPv6 address types.


Unicast Address:

•  Address is for single interface.
•  IPv6 has several types (for example: global and IPv4 mapped)

Broadcast storm.
Broadcasting in IPv4 results in a number of problems. Broadcasting generates a number of interrupts in every computer on the network and in some cases triggers malfunctions that can completely halt an entire network. This disastrous network event is known as "Broadcast Storm".

In IPv6 , broadcasting does not exist. Broadcasts are replaced by multicasts and anycasts.

Multicast Address: 

• One to many.
• Enables more efficient use of the network.
• Uses a larger address range.

Multicast enables efficient network operations by using a number of functionality specific multicast groups to send requests to a limited number of computers on the network.

The multicast groups prevent most of the problems that are related to broadcast storms in IPv4. The range of multicast addresses in IPv6 is larger than in IPv4.

For the foreseeable future, allocation of multicast groups is not being limited.

Anycast Address.


IPv6 also defines a new type of address called an "anycast address". An anycast address identifies a list of devices or nodes; therefore, an anycast address identifies multiple interfaces.

A packet sent to an anycast address is delivered to the closest interface as defined by the routing protocol in use- Identified by the anycast address.

Anycast addresses are syntactically indistinguishable from global unicast addresses because anycast addresses are allocated from the global unicast address space.

NOTE: Anycast addresses must not be used as the source address of an IPv6 packet.

• One-to-nearest (allocated from unicast address space).
• Multiple devices share the same address.
• All anycast nodes should provid uniform services.
• Source devices send packets to anycast address.
• Routers decide on closest device to reach that destination.
• Suitable for load balancing and content delivery services.

IPv6 global Unicast (and anycast) addresses.


IPv6 has same address format for global unicast and for anycast addresses.

• Uses a global routing prefix- a structure that enables aggregation (route summarization) upward, eventually to the ISP.
• A single interface may be assigned multiple addresses of any type (Uni-cast, anycast, multicast).
• Every IPv6-enabled interface must contain at least one loopback (::1/128) and one link-local address.
• Optionally, every interface can have multiple unique and global addresses.
• Anycast address is a global unicast address assigned to a set of interfaces (typically on different nodes).
• IPv6 anycast is used for a network multihomed to several ISPs that have multiple connections to each other.

The global unicast and the anycast share the same address format. The unicast address space allocates the anycast addresses. To devices that are not configured for anycast, these addresses appears as unicast addresses. When a unicast address is assigned to more than one interface, thus turning it into an anycast address, the nodes to which the address is assigned must be explicitly configured to use and recognize the anycast address.