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Auto-site assignment and multiple IP addresses

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.

Comments
  • Hi Carol,

    I don't think this is a significant techncial change and here is why.

    Would knowing the correct behavior change an administrator’s decision about whether to use auto-site assignment when a computer has multiple addresses?  

    This would require that the site boundaries were IP boundaries and would require that a potential client was connected and had two IP's and that one of the IP's was outside of the boundaries.

    From what I see with customers they usually don't use the /AUTO switch with client installations using client push, GPO, batch files, so on.  They put in the site code, and why not.  Assuming they did use the /AUTO switch it would still mean that there was a 50% chance on the first try they are going to find the site code.  And how often will a client installation take place where a potential client is using more than one IP?  Over VPN? a wireless network?  Those don't describe most client installations these days, it is done as part of the OSD process, through a package (can't get that if you are outside the sites boundaries), or through the console.  So it is possible if they push the client from the console or with client push.  If they are using the client push there is a 50% chance they are going to get it tomorrow, if it is done by right clicking on a collection it still tries to find the site, it may find it before it gives up, 25 hours later, I forget how long it tries.

    So the odds are pretty high that it will get the client.

    Would this information provide the missing information about why auto-site assignment failed?  

    Yes, it would.  I have seen this questions come up a few times and I have told customers the first bound NIC rule.

    Regards,

    Anthony

  • PingBack from http://configmgr.com/auto-site-assignment-and-multiple-ips/

  • Carol posted this over the the TechNet blogs site a couple of hours ago. I commented that I didn't

  • As I was the customer reporting this topic, I just want to let you know that we are actually trying to get a DCR for this because as a result, about 5% of our clients are unmanaged and we have to use another product to patch these clients.

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