# IPv6 Subnetting and Reserved Prefixes
###### tags: `elearning` `Multimedia Wireless Network`
###### Note Page : [:link:](https://hackmd.io/@YTL0307/HJEb6jWCo)

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## **IPv6 Subnetting**
- The process of subnetting IPv6 addresses is basically the same process as subnetting IPv4 addresses.
- That subnetting is used to create multiple broadcast domains that are smaller than your entire network.
- For instance, you may decide that you only want to have a certain number of hosts in each subnet. You create a subnet by changing the mask assigned to each broadcast domain. Your global routing prefix does not change.
- By extending the length of the subnet ID, you will have fewer hosts or interfaces in each subnet.
- The /116 prefix length leaves 12 bits for the interface ID
- This will allow for 4096 addresses in the subnet.
- The only exception to this rule is when you are defining a /127 prefix length for a point-to-point link. A /127 prefix length only allows for two IPv6 addresses, so you will need to be able to use both of them.
- Now, say that you would like to create a smaller subnet
- If we extend the prefix length by 4 more bits, there are only 8 bits left for the interface ID, which will allow for 256 valid addresses in the subnet.
- But, maybe that isn't enough. What if you wanted to create a subnet that had more than 256 addresses but less than 4,096?
- To visualize the subnet mask for a prefix length that does not fall on a 4-bit boundary, you will need to look at the address in binary.
- Here is what the /116 address looks like in binary.
- Now, suppose we want to extend the prefix length by just one bit, to a prefix length of 117. This leaves 11 bits for the unique IP addresses in this subnet.
- Here are the first and last addresses in this subnet range shown in binary.
- And here is the range shown with binary converted back to hexadecimal. A subnet with a prefix length of 117 will give you 2,047 valid addresses

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## **Reserved Prefixes**
- Just like with IPV4, certain prefixes are reserved and should be used for specific types of traffic.
- RFC 4291 defines the latest rules regarding prefix notation.