IPv6 (Part 1)

Day 31

IPv6

An IPv6 address is 128 bits long. It uses the slash (/) notation to indicate the prefix length.

IPv6 addresses can be abbreviated:

  • Leading 0s (zeros) can be removed, e.g. 2001:0db8:000c:002b:201b:0020:0080:34bd becomes 2001:db8:c:2b:201b:20:80:34bd

  • Consecutive quarters of all 0s (zeros) can be replaced with a double colon (::), e.g. 2001:0db8:0000:0000:0000:0000:0080:34bd becomes 2001:0db8::0080:34bd. And if both methods are combined it becomes 2001:db8::80:34bd. But it can be used only once per address.

Here are a few more examples:

Prefix

The enterprise requesting an IPv6 address from the ISP receives a /48 block address. IPv6 subnets use a /64 prefix length. So, the enterprise has 16 bits to make subnets. The remaining 64 bits can be used for the host portion. Even if the prefix length is not /64, if it is a multiple of 4, it is easy to find the prefix length because each hexadecimal character is 4 bits. Here is an example of how to find a network address of the host using the prefix length other than /64:

But if the prefix length is not a multiple of 4, you have to go through some extra steps to find a network portion.

Here are a few more examples:

Configuration

First, to enable IPv6 routing on the router, enter the command ipv6 unicast-routing from the global config mode. Then, to assign an IPv6 address on an interface, enter the interface config mode and use the command ipv6 address followed by an address and a prefix length. A shortened version of the address can also be entered. To check the IPv6-enabled interfaces, use the command show ipv6 interfaces brief. Each interface is also automatically assigned a link-local address when an IPv6 is enabled on the interface.

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