We have noticed that Windows seems to try to send ARP requests over
Wintun interfaces. In our configurations, these don't go anywhere and
get no responses, but the ARP table fills up with addresses. For example:
$ arp -a -N 10.0.0.100 |wc -l
387
Our Wintun interfaces are created with these properties:
PS C:\> Get-NetIPInterface -InterfaceIndex 69 |Select-Object -Property
AddressFamily,NeighborDiscoverySupported,NeighborUnreachabilityDetection |fl
AddressFamily : IPv6
NeighborDiscoverySupported : Yes
NeighborUnreachabilityDetection : Enabled
AddressFamily : IPv4
NeighborDiscoverySupported : Yes
NeighborUnreachabilityDetection : Enabled
We _think_ that the NeighborDiscoverySupported property being Yes means
that Windows issues ARP requests for addresses on the Wintun interface.
(The second property controls another neighbour behaviour that perhaps
could also be disabled for Wintun interfaces.)
Microsoft's documentation for SetIpInterfaceEntry() claims that these
properties are set "by the network stack", but offers no hint as to what
part of the network stack does this. It does not seem possible to
change these properties on an existing interface.
Are these properties that either the Wintun driver or user-space API is
able to control? Should they be set to No and Disabled? I don't see
any use of the driver variant of SetIpInterfaceEntry() or
MIB_IPINTERFACE_ROW in Wintun's driver or API code, so I'm not sure when
these properties get determined.
--
Brad Spencer
