This section covers IPv6 design topics that a CCNP enterprise designer should be aware of: planning for IPv6 addressing, IPv6 route summarization, IPv6 address allocation, and IPv6 private addressing. Some IPv6 design concepts are similar to those in IPv4 (such as the goal to do summarization), and some concepts are unique to IPv6. As with IPv4, each company will have a unique set of requirements that will drive the allocation and subnetting of the IPv6 address space.
Planning for Addressing with IPv6
When you are designing LAN subnets with IPv6, it is recommended that you use a /64 subnet. This is similar to the /24 subnet in IPv4. It provides more than enough addresses for devices contained in the subnet, allows for future growth, and prevents renumbering in the future. It also allows for easier aggregation of subnets.
If you are allocated IPv6 addresses from an Internet service provider (ISP), you most likely will have to renumber your IPv6 addresses if you move to a different ISP. The best way to avoid renumbering is to obtain an IPv6 address block from a Regional Internet Registry (RIR). This way, your IPv6 addresses are independent of which ISP you use. Address allocations are from the 2000::/3 global unicast block. The five RIRs are
- AfriNIC: Africa
- APNIC: Asia Pacific
- ARIN: Canada, the United States, and part of the Caribbean islands
- LACNIC: Latin America and part of the Caribbean islands
- RIPE NCC: Europe, the Middle East, and Central Asia
Route Summarization with IPv6
As a designer, you will want to allocate IPv6 address space to allow for route summarization. Large networks can grow quickly from 500 routes to 1000 and higher. Route summarization reduces the amount of route traffic on the network and unnecessary route computation, regardless of whether IPv4 or IPv6 addressing is used. Route summarization enables the network address space to scale as the company grows.
As an example, say a company has assigned the following IPv6 subnets to a site:
- 2001:db8:2a3e:8180::/64 for data networks
- 2001:db8:2a3e:8184::/64 for VoIP networks
- 2001:db8:2a3e:8188:/64 for wireless networks
- 2001:db8:2a3e:818F::/64 for small server farm and other systems
Instead of announcing each and every subnet of this network to the WAN, the recommendation is to summarize the site with a 2001:db8:2a3e:8180::/60 route. This summary encompasses 16 subnets from 2001:db8:2a3e:8180::/64 to 2001:db8:2a3e:818F::/64, so this address block would be assigned to this site.