How to REALLY reset DHCP on a wireless client?

Discussion in 'Wireless Networking' started by =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 27, 2007.

  1. I have two wireless routers, at different locations, which have a VPN
    established between them.

    If I take a laptop from location 1 to location 2 it continues to use the
    location 1 router (which is visible through the VPN) as the default gateway,
    DHCP server, and DNS server - leading to degraded performance.

    The association with location 1 persists through reboots, ipconfig/reset and
    /renew, and Wireless Network Connection Repair. Apparently the ip address of
    the DHCP server is being remembered somewhere.

    The easiest way I have found to break the association is to disconnect the
    router from the modem, and then do a Wireless Repair. As the router at
    location 1 is no longer visible the laptop hooks up with the router at
    location 2. During this process a number of messages flash past on the
    "Repair Wireless Network Connection" dialog box. These messages detail a
    number of things that are being reset - but they zip by too fast to read.

    Does anyone know what is being reset during this process, and how I can do
    it by hand without breaking the network?
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 27, 2007
    #1
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  2. Hi
    Which OS?
    What are you using to manage the Wireless.
    It is Not a DHCP issue. Your Laptop probably stays in a state that it
    preferred to be associated with the first Router's SSID.
    Jack (MVP-Networking).

    "Dave Nuttall" <> wrote in message
    news:...
    >I have two wireless routers, at different locations, which have a VPN
    > established between them.
    >
    > If I take a laptop from location 1 to location 2 it continues to use the
    > location 1 router (which is visible through the VPN) as the default
    > gateway,
    > DHCP server, and DNS server - leading to degraded performance.
    >
    > The association with location 1 persists through reboots, ipconfig/reset
    > and
    > /renew, and Wireless Network Connection Repair. Apparently the ip address
    > of
    > the DHCP server is being remembered somewhere.
    >
    > The easiest way I have found to break the association is to disconnect the
    > router from the modem, and then do a Wireless Repair. As the router at
    > location 1 is no longer visible the laptop hooks up with the router at
    > location 2. During this process a number of messages flash past on the
    > "Repair Wireless Network Connection" dialog box. These messages detail a
    > number of things that are being reset - but they zip by too fast to read.
    >
    > Does anyone know what is being reset during this process, and how I can do
    > it by hand without breaking the network?
    Jack \(MVP-Networking\)., Apr 27, 2007
    #2
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  3. > Which OS?
    > What are you using to manage the Wireless.
    > It is Not a DHCP issue. Your Laptop probably stays in a state that it
    > preferred to be associated with the first Router's SSID.
    > Jack (MVP-Networking).


    Hi Jack,

    Apologies for not providing that - the laptops are running either XP Pro or
    XP Home. The one I am using for troubleshooting is XP Pro.

    The locations are 20 miles apart, so there is no choice on the wireless
    front - the laptop uses the local router for the wireless service.

    It seems that, even if the address lease has expired, the laptop remembers
    who the DHCP server was, and specifically asks that router for a new address
    - hence my categorizing it as a DHCP issue.

    Best regards,

    Dave
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 27, 2007
    #3
  4. Hi
    How the Laptop is set, Obtain Auto IP and DNS, or Static configuration?
    The computer need to obtain an IP from the second Router otherwise it can
    not connect and see any thing at all.
    What VPN established means? To Routers need functional computer to establish
    active VPN unless they are special End Point Router.
    Jack (MVP-Networking).

    "Dave Nuttall" <> wrote in message
    news:...
    >> Which OS?
    >> What are you using to manage the Wireless.
    >> It is Not a DHCP issue. Your Laptop probably stays in a state that it
    >> preferred to be associated with the first Router's SSID.
    >> Jack (MVP-Networking).

    >
    > Hi Jack,
    >
    > Apologies for not providing that - the laptops are running either XP Pro
    > or
    > XP Home. The one I am using for troubleshooting is XP Pro.
    >
    > The locations are 20 miles apart, so there is no choice on the wireless
    > front - the laptop uses the local router for the wireless service.
    >
    > It seems that, even if the address lease has expired, the laptop remembers
    > who the DHCP server was, and specifically asks that router for a new
    > address
    > - hence my categorizing it as a DHCP issue.
    >
    > Best regards,
    >
    > Dave
    Jack \(MVP-Networking\)., Apr 28, 2007
    #4
  5. > How the Laptop is set, Obtain Auto IP and DNS, or Static configuration?
    > The computer need to obtain an IP from the second Router otherwise it can
    > not connect and see any thing at all.


    Thye laptops are all set with Obtain Auto IP and DNS. I believe that the
    problem is caused by XP remembering the IP address of the DHCP server even
    through an ipconfig/reset.

    > What VPN established means? To Routers need functional computer to establish
    > active VPN unless they are special End Point Router


    The routers are running DD-WRT with OpenVPN. One is configured as the VPN
    server, the other as the VPN client. They are set up so that the two
    locations are bridged - they appear as a single network. The routers use
    DynDNS to keep track of their actual IP addresses. The laptops see only the
    internal IP addresses - 192.168.0.1 and 192.168.0.2 for the routers at
    location 1 and location 2 respectively.
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 28, 2007
    #5
  6. Hi
    I never encounter such a phenomenon.
    If it was my system I would first suspect that it has to do with the DD-WRT
    and OpenVPN.
    Some of the "Fancy" add On to DD-WRT are not bug clean.
    I would first neutralized this setting and see if the same issue occurs with
    a regular connection.
    Or just try the Laptop with some normal Hotspot at your local Internet Café
    and see if it does the same.
    Jack (MVP-Networking).

    "Dave Nuttall" <> wrote in message
    news:...
    >> How the Laptop is set, Obtain Auto IP and DNS, or Static configuration?
    >> The computer need to obtain an IP from the second Router otherwise it can
    >> not connect and see any thing at all.

    >
    > Thye laptops are all set with Obtain Auto IP and DNS. I believe that the
    > problem is caused by XP remembering the IP address of the DHCP server even
    > through an ipconfig/reset.
    >
    >> What VPN established means? To Routers need functional computer to
    >> establish
    >> active VPN unless they are special End Point Router

    >
    > The routers are running DD-WRT with OpenVPN. One is configured as the VPN
    > server, the other as the VPN client. They are set up so that the two
    > locations are bridged - they appear as a single network. The routers use
    > DynDNS to keep track of their actual IP addresses. The laptops see only
    > the
    > internal IP addresses - 192.168.0.1 and 192.168.0.2 for the routers at
    > location 1 and location 2 respectively.
    Jack \(MVP-Networking\)., Apr 29, 2007
    #6
  7. > I never encounter such a phenomenon.
    > If it was my system I would first suspect that it has to do with the DD-WRT
    > and OpenVPN.
    > Some of the "Fancy" add On to DD-WRT are not bug clean.
    > I would first neutralized this setting and see if the same issue occurs with
    > a regular connection.


    Hi Jack,

    I caught the action using a sniffer - and it is an MS issue. I'll post
    details as a reply to the original post...

    Thanks,

    Dave
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 30, 2007
    #7
  8. Digging into what happens when you do an ipconfig/reset and then an
    ipconfig/renew shows the following in the first message sent out on the
    ipconfig/renew:

    Option: (t=53,l=1) DHCP Message Type = DHCP Discover
    Option: (t=116,l=1) DHCP Auto-Configuration
    Option: (t=61,l=7) Client identifier
    Option: (t=50,l=4) Requested IP Address = 192.168.0.106
    Option: (t=12,l=4) Host Name = "Dave"
    Option: (t=60,l=8) Vendor class identifier = "MSFT 5.0"

    As you can see, the client has remembered the previous IP address (not the
    DHCP server address as I originally suspected), and is requesting it again.

    So the question becomes, how can I force the laptop to forget it's previous
    IP address - given that ipconfig/reset does not do this?
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, Apr 30, 2007
    #8
  9. Hi,

    Haven't tested this, its just an idea, you could set the ip range for DHCP
    on the first router to 192.168.0.1-192.168.0.100 say, and then the range on
    the second to 192.168.0.101-192.168.0.255 ?? That way the requested IP wont
    be avaliable and it would have to get another one?

    As i said, just an idea.

    Will












    "Dave Nuttall" wrote:

    > Digging into what happens when you do an ipconfig/reset and then an
    > ipconfig/renew shows the following in the first message sent out on the
    > ipconfig/renew:
    >
    > Option: (t=53,l=1) DHCP Message Type = DHCP Discover
    > Option: (t=116,l=1) DHCP Auto-Configuration
    > Option: (t=61,l=7) Client identifier
    > Option: (t=50,l=4) Requested IP Address = 192.168.0.106
    > Option: (t=12,l=4) Host Name = "Dave"
    > Option: (t=60,l=8) Vendor class identifier = "MSFT 5.0"
    >
    > As you can see, the client has remembered the previous IP address (not the
    > DHCP server address as I originally suspected), and is requesting it again.
    >
    > So the question becomes, how can I force the laptop to forget it's previous
    > IP address - given that ipconfig/reset does not do this?
    =?Utf-8?B?RmFpcnlfUHJpbmNlc3M=?=, Apr 30, 2007
    #9
  10. >
    > Haven't tested this, its just an idea, you could set the ip range for DHCP
    > on the first router to 192.168.0.1-192.168.0.100 say, and then the range on
    > the second to 192.168.0.101-192.168.0.255 ?? That way the requested IP wont
    > be avaliable and it would have to get another one?
    >

    That is very close to what I have set up - router 1 does .100-.149, and
    router 2 does .150-.199.

    Let's say I'm at location 1 with an IP address of .106. When I go to
    location 2 (the lease will expire during the journey), XP asks for .106
    again. Router 2 ignores this (as it is out of its address range), but router
    1 gets the request over the VPN and responds. Now I have a computer at
    location 2 using the router at location 1 - with the associated delays.

    The issue I have is that I can't find any way to stop XP from asking for
    ..106. Temporarily breaking the link between router 1 and router 2 during the
    DHCP negotiation is a solution - but it involves breaking the network.
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, May 1, 2007
    #10
  11. > Does anyone know what is being reset during this process, and how I can do
    > it by hand without breaking the network?


    The answer is ipconfig/release followed by a reboot. It seems that the old
    IP address is being stored in memory (it's not in the registry or any file
    that I could find), so a reboot clears this also.
    =?Utf-8?B?RGF2ZSBOdXR0YWxs?=, May 18, 2007
    #11
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