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I work on the c-ares open source asynchronous DNS library (https://c-ares.org) and we have recently added automatic configuration reloading when we detect a network configuration change has occurred.
We get notifications properly when network interfaces go up or down, or IP addresses change (e.g. DHCP), but we aren't getting notifications for a user manually changing a DNS server via Control Panel -> Network and Internet -> Network Connections, then right click on an interface and go to properties then modify the DNS server in "Internet Protocol Version 4 (TCP/IPv4)" or "Internet Protocol Version 6 (TCP/IPv6)".
We used NotifyIpInterfaceChange() for this (https://learn.microsoft.com/en-us/windows/win32/api/netioapi/nf-netioapi-notifyipinterfacechange), which the documentation seems to indicate since we made a change to the interface we should be notified, however no notification is sent. We would expect to get a MibParameterNotification.
We also tried using NotifyUnicastIpAddressChange() but that didn't notify on that condition either.
This was tested on an up-to-date Windows 11 development machine. I would consider this a bug in NotifyIpInterfaceChange() since it doesn't match the description in the documentation.
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There is no NotifyIpInterfaceChange identifier when I include the Iphlpapi.h header.
Update: reproduced with the following code in a Windows desktop application. Exactly to say, I cannot make the callback triggered including changing a DNS server via Control Panel -> Network and Internet -> Network Connections.
#include <ws2tcpip.h>
#include <iphlpapi.h>
VOID
(NETIOAPI_API_ MyCallback) (
_In_ PVOID CallerContext,
_In_ PMIB_IPINTERFACE_ROW Row OPTIONAL,
_In_ MIB_NOTIFICATION_TYPE NotificationType
)
{
}
HANDLE h{};
DWORD d = NotifyIpInterfaceChange(AF_UNSPEC, MyCallback, NULL, FALSE, &h);
Glad you were able to confirm my findings. Where do we go from here?
Hello Brad,
The documentation is not specific about exactly which type of events/changes trigger a notification. A quick look at the behaviour and binary code suggests that the notifications relate to the kernel-mode aspects of network interfaces. The name server settings are a purely user-mode concern.
I traced the user-mode behaviour and there does not seem to be any general notification feature. One can see that dnsapi!Reg_SetValuePropertyAndAlertCache calls dnsapi!DnsNotifyResolverEx, but this notification is just an RPC to the Dnscache service.
What one could do is to use a routine like RegNotifyChangeKeyValue to monitor the HKLM\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\Interfaces and HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces keys.
Gary
@Gary Nebbett Thanks for the hint regarding RegNotifyChangeKeyValue, I'll look into that and see if I can use that. We're currently using GetAdaptersAddresses() to retrieve the DNS server configuration but if that is really pulling in some data stored in the registry then that sounds like a viable workaround.
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Hello Brad,
This is the list of reasons that I think trigger a NotifyIpInterfaceChange callback:
<valueMap name="IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap">
<map value="0" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.InterfaceAddition)" />
<map value="1" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.InterfaceDeletion)" />
<map value="2" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ZoneChange)" />
<map value="3" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ConfigurationFlagChange)" />
<map value="4" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ForwardingEnable)" />
<map value="5" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ForwardingDisable)" />
<map value="6" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.WeakHostReceiveEnable)" />
<map value="7" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.WeakHostReceiveDisable)" />
<map value="8" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.NetworkCategoryStateChange)" />
<map value="9" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.MetricChange)" />
<map value="10" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.MediaConnect)" />
<map value="11" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.MediaDisconnect)" />
<map value="12" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.OffloadCapabilityChange)" />
<map value="13" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.DisableDefaultRoutesSet)" />
<map value="14" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.DisableDefaultRoutesReset)" />
<map value="15" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ForceTunnelingSet)" />
<map value="16" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.ForceTunnelingReset)" />
<map value="17" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.LimitedLinkConnectivitySet)" />
<map value="18" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.LimitedLinkConnectivityReset)" />
<map value="19" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.LocalityConfigChange)" />
<map value="20" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.RoutingFlagsSet)" />
<map value="21" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.RoutingFlagsReset)" />
<map value="22" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.PortStateChange)" />
<map value="23" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.RscUnawareIpsnpiClientPresent)" />
<map value="24" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.RscUnawareIpsnpiClientAbsent)" />
<map value="25" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.PromiscuousModeEnabled)" />
<map value="26" message="$(string.valueMap.IP_INTERFACE_CHANGE_NOTIFY_REASON_ValueMap.PromiscuousModeDisabled)" />
</valueMap>
Gary
Hello @Brad House,
Where do we go from here?
If the issue has a big impact on you, you can open a Windows SDK incident at https://developer.microsoft.com/en-us/windows/support/?tabs=Contact-us so that our engineer can work with you closely and please choose the 'Networking Development - Internet Protocol Helper (IP Helper) API' for this issue. In-addition, if the support engineer determines that the issue is the result of a bug the service request will be a no-charge case and you won't be charged.