Recommendation: Migration to IPv6 Preparation Cleaning Up IPv4

General Considerations

1. Cleanup IPv4 - Clean up current IPv4 Implementations.

• It is much easier to implement IPv6 as an overlay onto a well-designed (ie: hierarchical) IPv4 and VLAN-segmented network.
• Cleanup and verify current IPv4 network design, DHCP, DNS, and documentation before IPv6 migration.
• Create location-centric VLANs as this shrinks the size of broadcast domains, simplifies the spanning-tree topology, and maps directly to a location-centric hierarchical address scheme.
• Push the layer 3 edge / IP gateway as close to the end device as possible – this may be to the distribution or access layer depending on design & requirements in order to reduce complexity.
• Route large blocks of addresses to network segments based on physical/logical location – create an addressing hierarchy to break down large IP blocks into smaller pieces as networks segment.

For example, in an IPv4 access/user environment (if you have the IPv4 address space):

• Use a /20 block for a large “parent” network segment like a two-story building
• Break that /20 block down into a /21 per floor (for a 2 story building)
• Per floor, use /24’s for specific use types (to get 8 networks per floor)
• Scale up the /20 block to a /19 or /18 depending on how many floors, networks per floor, etc. are required.

Table 1 Example of IPv4 Summarization

The following considerations apply to DMZ networks, Datacenter Networks – especially layer 3 - send a large block of addresses to a router, and break it down into smaller segments as necessary.

• Summarize address space before sending to upstream routers – don’t send a large number of /24’s, send the parent /20.
• Remember as long as dual-stack is engaged, IPv4 broadcast domains still apply.
• VLANs can be better organized in this layout as every category of network can have the same VLAN#. Ie; all “Data” networks can have VLAN 100, all “Printer” networks can have VLAN 101 etc.