Network World: Five old wives' tales about ATM addressing

ATM address formats are irrelevant.

ATM address formats could be considered immaterial if, and only if, your network is not, and never will be, connected to another ATM net.

My ATM network will never be connected to any other.

If you really believe this, you must be living in another generation. Networks want to interconnect. The network that is stand-alone now and will remain that way is rare indeed.

All ATM address formats are created equal.

This is analogous to Myth No. 2. Different ATM address formats were designed for different purposes (see graphic, page 41). True, the formats all consist of a series of octets -- basically, groups of bytes - and many of the formats are similar in nature. However, the format distinctions matter now and will matter even more as ATM networks continue to spider web together.

Rolling your own addresses makes sense.

For networks that do not connect to other networks, addressing can be a matter of organizational preference. It is also true that rolling your own address format gives your network all 20 bytes in the ATM address to use without restriction. But when the time comes to interconnect your ATM net with another, you'll likely get a registered Network Service Access Point and have to change all the addresses in your network. So it probably makes sense to use registered addresses from the get-go.

It's OK to use the format that comes installed on your ATM switches.

You would be amazed at how common it is for network designers to deploy the addresses that happen to come out of the box with their ATM switches. Even major carriers have made this goof. This Russian roulette scheme is fraught with danger. First, you are depending on the equipment vendor not to duplicate addresses on multiple switches.

Some vendors maybe careful about this, but don't count on it. In addition, you can forget about using a contiguous address range; the next switch in the sequence may have gone to another customer. Imagine the fun you will have should you happen to connect to that customer's network sometime in the future.