December 11, 2000, 3:44 PM — In my past two columns I've talked about why implementing IPv6 on your network is a good idea, and delved deep into the IPv6 header. I'll now conclude this series with a detailed look at IPv6 addressing conventions.
IPv4 addresses, which use dotted decimal notation, are fairly easy to remember. With a maximum of four octets -- IPv4 has a 32-byte address field -- and decimal representation of the numbers, IPv4 addresses resemble a telephone number. 126.96.36.199 -- that's fairly easy to read and remember.
IPv6 addresses, on the other hand, use hexadecimal notation. Version 6's implementers chose this over the easier-to-read decimal notation to save space. Hexadecimal notation allows 8 bits of data to be represented by two characters.
If you've forgotten what hexadecimal notation is, here's a quick refresher. Hexadecimal, or base 16, notation uses the digits 0-9 and the letters A-F to represent the digits 0-15. Thus, 12 = 0Ch, and 5x7 = 23h. It's not a difficult conversion, but a calculator that performs decimal-to-hex conversion makes it even easier. If you don't have one, I suggest you pick one up. I use the Texas Instruments TI-86.
A fully-expanded 128-bit IPv6 address would be written like this -- 3FFE:1CDD:10:30:0000:0000:0000:1212. Quite a handful, isn't it?
Fortunately, IPv6's designers allowed for a shorthand notation. As in IPv4, all zeroes to the left of any 16-bit field may be removed. Thus, 3FFE:1CDD:10:30:0000:0000:0000:1212 becomes 3FFE:1CDD:10:30::1212. This saves space, but only one double colon is allowed in an address.
Shortened or not, IPv6 addresses don't lend themselves to easy memorization. Don't fret, though; you can use the same naming conventions for IPv6 as you did for IPv4. BIND (Berkeley Internet Name Domain), the
application that provides IP address-to-name translation, has been modified to work with IPv6.
Now that I've covered IPv6 address notation, it's time to discuss how the addresses are divided among different-level aggregators.
IPv6 provides four levels of aggregation:
- The Top Level Aggregator (TLA) is used to identify the Top Level Aggregator to which the address block belongs. Typically, a TLA would be a big kahuna among network providers -- Sprint, for example. TLAs delegate portions of their address block down to Next Level Aggregators (NLAs).
- A Next Level Aggregator is an organization too small to qualify as a TLA, but with an extensive regional backbone and a number of small customers. NLAs break up their portion of the address blocks and delegate down to Site Level Aggregators (SLAs).