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On IPv6

A look at the changes in IPv6.


On IPv6
Fred Mallett

Most of you have seen IPv6 show up as a question when configuring software. Most are aware that it is a new addressing scheme to replace the 32 bit IP addresses (IPv4) we now use. If that is the extent of your knowledge, read on.

Let's start with the reasoning: There was a big worry a number of years back of how we would run out of IP addresses soon. It seems that with the number of sites turning unused addresses in (due to usage of RFC1918 addresses behind a firewall), this was not as immediate a problem as it appeared. IPv6 addressing uses 128 bits. In addition to adding more space in general, some of the added bits are to provide info assisting with routing, and configuring.

The breakdown of address bits are as follows:

Bits 1-3 Type of address (Uni, multi, any-cast)
Bits 4-16 TLA ID

The Top Level Aggregate Identifier will identify locality, to some degree. This will identify a top-level backbone carrier.

Bits 17-24 Reserved
Bits 25-48 NLA ID

The Next Level Aggregation ID will identify regional ISP's and possibly Site ID.

Bits 49-64 SLA ID

The Site Level aggregation ID is planned to be used for local subnets.

Bits 65-128 INTERFACE ID (MAC address plus...)

There are some issues with the planned use of putting the MAC address as part of the IP address. On the good side, hosts can be fairly easily self configuring, all they need to be supplied is the upper 64 bits, possibly getting that from a router, and they can determine their own lower half address from the interface card. The drawback is that it is easy to determine the host type of some machines by looking at the MAC address. The IPv6 committee replies that you are not required to use the MAC address as part of the IP address.

Many upper level ISP's are starting to implement IPv6. Most major vendors are shipping IPv6 capable hardware, so it is time to start becoming familiar. A good site to look further into this is

Fred Mallett is founder of FAME Computer Education, which provides standup delivery of educational classes on a variety of UNIX and Win32 related subjects.

This was last published in March 2002

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