I'm new to Hyper-V, so it will be difficult for me to describe the problem. But i'll try to :)

There's Server 2012 with 2 NICs: one looking to lan, another is connected to ADSL modem. RRAS is already configured on the server, with Remote Router interface (on-demand PPPoE connection). Everything works fine: lan clients have access to internet through the server. Now we are installing Hyper-V. To give access from VMs to lan and Internet we have to add External Virtual Switch over the NIC, which looks into lan, yes? But in that case client computers from local network do not have access to Internet.

Any ideas?