Can't connect to wifi on different subnets  with pumps

Posted on 2012-09-18
Last Modified: 2012-11-12
We have a bunch of  CareFusion  Alaris pumps that we need to connect to our WIFI units (Meraki MR16).  We have 3 subnets in our facility. (main switch, dns/dhcp resides on this subnet.  first floor second floor
These pumps will connect to the wifi on the subnet but will not connect to the wifi’s on the or the subnet.  We statically assigned them an ip and then they will connect but these will be roaming from floor to floor so that won’t work in production.  We don’t have this issue with any other devices using the wifi ie..  laptops, iphones, ipads.  
So if I plug my POE access point into a port running the pump grabs an ip from dhcp and life is good.  When I move that access point to or and turn the pump on it does show the wifi signal strength but never receives an ip address.  The display on the pump shows Associated for 1 minute than dissociated flashes than back to associated.
Any ideas?
Question by:HBMI
    LVL 25

    Expert Comment

    by:Fred Marshall
    Well, you haven't revealed how the SSIDs are set up.  Is it all one SSID or are there 3 of them?

    If one SSID then signal strength could cause switching of subnets.

    If 3 SSIDs then you have to have each one set up to connect automatically to each SSID / passphrase (if used), etc.    Then they can connect at least.
    I can imagine that the "associated" being intermittent like that means it's trying to FULLY connect (meaning 1) connect at the radio level and then 2) satisfy the security requirements and then 3) get an IP address.  And, what you're seeing is success at level 1 but not at level 2.
    This is rather common behavior depending on the wireless software on the client.

    What I don't know, and again this would be dependent on the client software (i.e. the pump wireless software), is what might cause them to switch from one wireless site to another.  Certainly lack of signal will do this but maybe the signals are all strong throughout the building.  That other devices seem to do OK in this regard suggests that this isn't TOO big a problem.  So that takes me back to setup, security, and individual device behavior (software).

    I presume that the pumps don't have a firewall?  So the notion of different subnets wouldn't seem to be an issue here.  If these were computers then it might well be depending on the firewall software in use on the computer.  Apparently you've not run into that with other devices ... interesting.

    Author Comment

    The issue isn't that they connect to a different subnet but rather they want to be able to move the pumps from floor to floor so they should be able to connect to the wifi's on any floors.  All of the ssid's and passphrases are the same.
    LVL 25

    Expert Comment

    by:Fred Marshall
    The issue isn't that they connect to a different subnet but rather they want to be able to move the pumps from floor to floor so they should be able to connect to the wifi's on any floors.  All of the ssid's and passphrases are the same

    I'm just a little confused by this.  I thought the issue was that they *don't* connect to each of the various subnets.  My assumption is that you want these devices to be on the subnet that's associated with the floor they are on.  Yes?

    If the SSIDs and passphrases are the same then how can you be sure that they won't pick up from one of the others by virtue of signal strength?  Being on the same floor may or may not mean having the highest signal strength from the access point on that floor.  Walls, and sources of noise vary.

    Most people have a different problem.  They just want to stay connected as they move things around.  In your case the problem is tougher because you want to have a *particular* connection that's wireless.  And, at that, the SSIDs are the same.
    Are the channels the same as well?

    Just to be clear, your objectives are:
    1) have one distinct subnet per floor
    2) roam devices between floors where each floor has an access point wired into the local (floor) subnet.
    3) access local floor subnet addresses on the wireless.

    I'm a bit afraid that the solution to this may be one you don't like:
    - you may be forced to use different SSIDs and force the connection you want.
    e.g. SSIDs of FLOOR1, FLOOR2 and FLOOR3.
    I'd have them on different channels just to avoid interference.
    How your devices can be controlled to do this will be an issue of course.  That would be very device specific (i.e. the pump interfaces settings, etc.)

    So, it does make me wonder about these devices and how they set up IP settings.  It almost sounds like a subnet mask issue but I can't imagine the devices caring about that.  The subnet masks are all correct?  How are you setting up the access points?
    They are simple devices plugged into the local LAN, yes?
    How do they get their own IP addresses?  DHCP or.....?
    How is DHCP handled on the wireless?  By the access point or some other local subnet (floor) DHCP server?

    Accepted Solution

    Found out that the time to live on the device is set to 1.  The router was dropping it after it changed subnets.

    Author Closing Comment

    Found this out by working with HP procurve techs.

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