(Ethernet, VPN, Wireless, and OS IP Gateway Table)
From Steve, Fri Jan 7 13:49:31 2005
There is a MS Windows networking scenario that everyone should be aware of in order to help people troubleshoot their network connections. With the advent of VPN and wireless networking the way MS Windows ultimately makes a network connection has changed. Buried in the MS Windows OS is a table which includes a default gateway IP.
If a user configures their laptop for both wireless and wired Ethernet consider this. They may have a wireless network at home and they have configured a wireless network connection with the network wizard. The OS must now allow the continual automatic changing of the IP the laptop can connect through as the laptop is moved through a series of wireless access points each with it's own IP.
The user now carries the laptop to their office at NMT which is outside the range of any of the access points in the IP range they were previously connecting to. In order for the laptop to now connect through a new default gateway the user must manually "disable" the wireless interface or it will perpetually continue to search for an access point with the same default gateway as the original wireless access point with which it had started.
"Disabling" a network connection in order to create a typical wired Ethernet connection is really a new concept for MS Windows users and is easily overlooked. Just "connecting" with the wired Ethernet port will not work as the default gateway in the internal table does not change. Only "disabling" the wireless connection forces the OS to look for a new default gateway IP which it will find if the user now "connects" with the wired Ethernet connection icon.
Overlaying a VPN connection on top of all this compounds the problem as the IP's of the other connections, both wired and wireless, appear to disappear and reappear as the VPN connection is made and broken. In fact the internal default gateway setting never changes during this process as the VPN client software temporarily supersedes the internal table.
At least this is my understanding and if anyone has further or differing knowledge on this please feel free to jump in and contribute any changes or additions.