Auto-site assignment and multiple IP addresses

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It happens to all of us. Just when you think you’ve comfortably nailed a certain aspect of the product – Kapow! – the rug is pulled from under your feet and you realize you’re not on the stable ground you thought you were. It’s all part and parcel of working with a complex product, but still disconcerting when it happens.

Well, I had one of those moments recently when a bug came in about multiple adapters and auto-site assignment. It has long been documented (way before I joined the team) that when a computer has multiple adapters (such as a wired adapter and a wireless adapter or modem), the adapter bound first will be used to determine the client’s boundary location during auto-site assignment.

This isn’t something that I’ve ever had to rely on myself – if a computer had multiple adapters I would always prefer to use a direct site assignment, and the docs say that in this scenario, auto-site assignment probably isn’t for you. But I’ve always trusted the “first bound adapter” information.

Now it turns out that this isn’t true. A customer reported that this didn’t seem to be the case with their SMS 2003 client – an adapter that was not bound first was being used for site assignment. The product team looked into it, and sure enough, this piece of information that I’ve always trusted was actually incorrect. When a computer has multiple adapters or multiple IP addresses, the ordering of the IP addresses was nondeterministic but consistent for a particular computer. The same number of adapters or IP addresses for another computer would usually result in a different but consistent ordering of the addresses.

Although the customer reported this with SMS 2003 and quoted the SMS 2003 Concepts, Planning and Deployment Guide as the source of their (mis)information, there are no plans to republish this documentation. However, I have corrected it for the Configuration Manager 2007 SP1 RC documentation, in the topic About Client Site Assignment in Configuration Manager.

Old text (incorrect)

Note:

If a Configuration Manager 2007 client has multiple network cards (possibly a LAN network card and a dial-up modem), and therefore has multiple IP addresses, the network card that is bound first is used for evaluating client site assignment.

New text (corrected)

Note:

If a Configuration Manager 2007 client has multiple network cards (possibly a LAN network card and a dial-up modem), and therefore has multiple IP addresses, the IP address used to evaluate client site assignment is nondeterministic.

This is undoubtedly a technical change to the topic, but it’s not noted in the What’s New in the Configuration Manager Documentation Library for March 2008 where we list new topics or significant technical changes. I deliberated whether this was a “significant technical change”, and taking into account that this has been incorrect in our documentation for nearly 5 years before anybody commented on it, I decided that it wasn’t. Then I remembered one of our product group’s mottos “Absence of evidence is not evidence of absence” and wondered if I had made the right decision.

Does anybody feel strongly that this constitutes a significant technical change? For example:

  • Would knowing the correct behavior change an administrator’s decision about whether to use auto-site assignment when a computer has multiple addresses?
  • Would this information provide the missing information about why auto-site assignment failed?

I suspect in practice that it’s one of those interesting pieces of information that you like to have clear in your mind, whether or not it’s actually of practical use. But if you think I made the wrong call and it qualifies as a significant technical change that should be called out in the change log topic, e-mail SMSDocs@Microsoft.com and I’ll see what I can do to retroactively list it.

And now, back to terra firma – until the next time!

 

- Carol Bailey

This posting is provided “AS IS” with no warranties and confers no rights.