The site prefix of an IPv6 address occupies up to 48 of the leftmost bits of the IPv6 address. You use the following representation, with zeros compressed, to represent this prefix:. You can also specify a subnet prefix , which defines the internal topology of the network to a router.
The example IPv6 address has the following subnet prefix. The subnet prefix always contains 64 bits. These bits include 48 bits for the site prefix, in addition to 16 bits for the subnet ID. The type of unicast address is determined by the leftmost high order contiguous bits in the address, which contain the prefix. The global unicast address is globally unique in the Internet.
The next figure shows the scope of the global unicast address, as compared to the parts of the IPv6 address. The site prefix defines the public topology of your network to a router. IN IPv6, the subnet ID defines an administrative subnet of the network and is up to 16 bits in length.
You assign a subnet ID as part of IPv6 network configuration. The subnet prefix defines the site topology to a router by specifying the specific link to which the subnet has been assigned.
IPv6 subnets are conceptually the same as IPv4 subnets, in that each subnet is usually associated with a single hardware link. However, IPv6 subnet IDs are expressed in hexadecimal notation, rather than in dotted decimal notation. The interface ID identifies an interface of a particular node. An interface ID must be unique within the subnet.
IPv6 hosts can use the Neighbor Discovery protocol to automatically generate their own interface IDs. One example of a transitional global unicast address is the 6to4 address.
For more information on 6to4 addressing, refer to 6to4 Automatic Tunnels. The link-local unicast address can be used only on the local network link. Link-local addresses are not valid nor recognized outside the enterprise. The following example shows the format of the link-local address.
Hexadecimal representation of the bit binary prefix This prefix identifies the type of IPv6 address as link local. When you enable IPv6 during Solaris installation, the lowest numbered interface on the local machine is configured with a link-local address.
Each interface requires at least one link-local address to identify the node to other nodes on the local link. The main reason for the development of IPv6 was to overcome the problem of IPv4 address exhaustion. With this issue in mind, the IETF also optimized the protocol in the general sense. With the rapid growth of internet devices—otherwise known as the Internet of Things IoT —around the globe, more IP addresses are required for these devices to exchange data. Think about mobile phones, smartwatches, refrigerators, washing machines, smart TVs, and other items that require an IP address.
All of these devices are nowadays connected to the internet and identified by a unique IP address. Today, it can be optionally used with IPv6. See RFC An IPv6 address is written in hexadecimal notation separated by the colon symbol : as shown here:.
It is important to note that if an address consists of multiple all-zero fields and those zeros occur in different parts of the IP, then the leftmost zeros are the ones that are compressed. The IPv6 address consists mainly of two bit segments where the higher part of the bits is classified as the network part, and the lower 64 bits are classified as the client ID.
This information can be simplified by the following picture:. It is worth noting that IPv6 has no notion of subnet masks like IPv4 has.
Examples are:. The Unicast address type is probably the most important one. It distinguishes itself by these sub-type addresses:. Multicast is the technique used to send a packet from one source or multiple sources to multiple destinations receivers. In its simplest form, a multicast flow is as follows.
First, a host sends an ICMPv6 packet host solicitation to the router s multicast group. Then, a router responds to this request and sends a Router Advertisement RA packet back to the client along with configuration parameters:.
The Anycast address behaves similarly to the Multicast address, except for the following. This is illustrated in the following example. Note that all underscored groups have at least on leading zero.
For groups 2,3 and 8, the rules are pretty straightforward, you just remove the leading zeros and that's about it. But if you look at group 4 for example, you cannot remove all four zeros, so the trailing zero highlighted in yellow must remain.
The shortest possible representation is achieved by combining both rules we have discussed. Let's get the IP address from example 3 and apply rule 1 and rule 2 at the same time. You can see that after we apply both rules, the resulting representation is significantly shorter. There are several common mistakes people make when they start applying these techniques. Let's look at several examples and highlight the key points.
In this example, in the original address, there are two consecutive strings of zeros, in groups 3 and 4, and in groups 6 and 7. People often try to replace both with :: and end up with two double colons in the shortened address. This is not allowed though, because it creates an ambiguous address representation. The other common mistake is to remove trailing zeros. Note the hex digits in group 2 - 0cb0, people often remove both 0s, but only the leading zero is allowed to be removed.
This is one appears very often in questions regarding IPv6 addresses. It is a valid address similar to 0. The above example is the well-knows v6 loopback address. This is the v6 alternative to the well-known The above example is the well-knows all-nodes multicast address.
The last example we are going to look at is a random link-local address. It is very important to understand both rules for shortening addresses and to be able to apply them correctly on any random IPv6 address. There are at least a few questions in the CCNA exam that are related in some way to this topic.
In IPv4, the network portion of the address is written as a dotted-decimal network mask such as Therefore, there is only one way to write an IPv6 prefix:.
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