Why won't my laptop reconnect to my wired network after using WiFi?

Question

I have a wireless and wired network in my house. My internet access is via ADSL using an Eircom supplied and branded Zyxel P-660HW-T1 v3 running:

ZyNOS firmware: 3.70(BOE.3)D0|03/30/2010
DSL Firmware: 3.11.11.245_A_TC

When I work in my home office I use my laptop to connect to the network using a wired connection (I'm wired for gigabit ethernet, the router hangs off this switch).

My laptop is a Dell Vostro 1720 running Windows 7 Ultimate 64-bit and it has an Intel 5300 AGN wifi interface and a RealTek 8168 PCIe GBE NIC.

Both interfaces have the same static private IP address but only one interface is used at a time.

In the evening I disconnect from the wired network take the laptop into the lounge and connect to my network using wifi. To do this I:

1. Unplug the ethernet cable
2. Disable the wired NIC in Control Panel -> Network Connections
3. Enable the wifi interface.
4. Connect to the wifi network using the notification area wireless network widget

This all works fine until I try and reconnect to the wired network in the office. When I reconnect to the office wired network I do:

1. Attach the ethernet cable
2. Disconnect from the wifi network using the notification area widget
3. Disable the wifi interface in Control Panel -> Network Connections
4. Enable the wired NIC

At this point something seems to break:

• I can ping all the devices on my private LAN just fine, including the the router
• I can't ping/tracert or connect to any external IP's e.g. 8.8.8.8

To resolve this I basically have to reboot the router and then all is well until the next day when I go through the same routine again.

When I do a tracert -d 8.8.8.8 the first hop is the router but I get no further than that and the requests time out.

Why would this be happening?

Answer 1

My first thought on this would be an address resolution protocol issue caused by two interfaces with different MAC addresses having the same IP in rapid succession. It may be that when you connect the cable low-level network functions are being carried out even though your ethernet NIC is disabled (for example, a PXE ethernet adapter might perform DHCP even though it is not enabled in the operating system). Do you get the same result if you disable the wireless adapter, enable the ethernet adapter, and then plug the cable in?