If you sometimes happen to see your PC or laptop not connecting to the internet at the startup and the only way you could get online is to disable and enable the network adapter, then one of the causes could be the Bonjour DNS responder service. This Bonjour, also called as “Zero Configuration networking” is installed as part of many software like Apple iTunes, iPhoto.
When this is installed, you would see a “unidentified network” in the network list and this could interfere with the network connectivity at system boot up. Hence, disable/enable network adapter would fix the problem only till the next reboot.
To resolve this problem,
1. Click Start – Search, type Services.msc and press Enter.
2. In the right-pane, look for
Bonjour service or "Id_String2.6844F930_1628_4223_B5CC_5BB94B87 976"
3. If you found any of these, right-click – select properties and click Stop. You should now see the “unidentified network” disappear from the list.
4. Select Startup type as “Disabled” and click apply-OK and the next time the system restarts, you shouldn’t see the unidentified network and hence the problem disappear.