IPv6 Address Design

Don't Let a Bad Design Sabotage Your Deployment Project

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At the same time, you might have need of some identifier digits within the Interface-ID, either for filtering at the subnet level or just for easy identification of device types within a subnet. In this case, use some of the leading bits in the Interface-ID, at the other end from the interface-specific bits, and again leave reserved zero space between. If you do use identifiers within the Interface-ID, they should be type identifiers. All location meanings should reside in the first 64 bits of the address preceding the Interface-ID.

The enormous 64-bit capacity of the Interface-ID leaves you plenty of room for identifiers, more than enough addresses per subnet, and the ability to keep your overall address manageably small.

Fun and Games with Hex

When I taught networking basics classes many years ago, I emphasized to my students that they should be careful about trying to interpret IPv4 addresses at the dotted decimal level; they should practice converting each of the four decimal numbers into their binary equivalent, until they became proficient at just looking at a number, say 240, and automatically seeing 11110000. The patterns of the bits tell you how a router interprets an IP address, not the decimal value representing the bits.

With a good design and no VLSM to obscure things, IPv6 is a bit easier to interpret at the hex level. But there are still plenty of good reasons to sometimes delve down to the individual bit values to look for a pattern. So the ability to quickly convert between hex and binary is just as important for working with IPv6 as converting between decimal and binary is for working with IPv4.

There are a few simple tricks that make these conversions fast and easy. (And no, you cannot count on always having a scientific calculator handy to do the conversions for you.) In the next post I’ll show you how.

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Copyright © 2011 IDG Communications, Inc.

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