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Design Considerations for IPv6

An IPv6 address space is not subnetted to conserve addresses; rather, it is subnetted to support hierarchical, logical design of the network. Whereas IPv4 subnetting is about managing address conservation, IPv6 subnetting is about building an addressing hierarchy based on the number of routers and the networks they support.

Subnetting an IPv6 Network

The subnet ID of an IPv6 address provides 16 bits for subnetting. That’s a total of 216 or 65,536 subnets—plenty of subnets for small to medium-sized businesses. In addition, each subnet has 64 bits for the interface ID. That’s roughly 18 quintillion addresses, obviously more than will ever be needed in one IP network segment.

Subnets created from the subnet ID are easy to represent because there is no conversion to binary required. To determine the next available subnet, just count up in hexadecimal, as shown in Figure 9-8.

Figure 9-8

Figure 9-8 Subnetting an IPv6 Address by Incrementing the Subnet ID

IPv6 Subnetting Practice

In practice, subnetting IPv6 is straightforward. The only possible difficulty is counting in hexadecimal as you increment the subnet ID.

IPv6 Subnetting Scenario 1

Assume that the network administrator allotted your section of the network four /64 IPv6 subnets starting with the subnet address space 2001:DB8:CAFE:F00D::/64. What would be the next three /64 subnets?

IPv6 Subnetting Scenario 2

Assume that the network administrator allotted your section of the network four /64 IPv6 subnets starting with the subnet address space 2001:DB8:CAFE:AA9F::/64. What would be the next three /64 subnets?

IPv6 Subnetting Scenario 3

Assume that the network administrator allotted your section of the network four /64 IPv6 subnets starting with the subnet address space 2001:DB8:CAFE:9EFD::/64. What would be the next three /64 subnets?

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