Hi
Let me clarify that the VPN(encryption) mostly runs between the clients location and not between the ISP and the client.
Also theres no point in encrypting normal traffic which will only hog the hardware resources on both the sides.
you need to be choosy while selecting the interesting traffic which really requires security in other words to be encrypted.often its the transactions/transfers which happens between the client sites which is connected thru same SP or different SPs.
So the required encryption is applied on the client side routers for the interesting traffic (which u choose to be encrypted).
Again you need to have same parameters configured on both the ends to have proper encryption and decryption process to happen.
Also before establishing the virutal tunnel lots of parameters like the key,hash etc .,needs to be mutually agreed .
AFAIK with the VPN concentrators you can have RAVPN connections established.
You can have remote dialin clients onto the box getting an ip from the local internal network and start accesing the the internal network.
Also if you use clients on the remote site you can also configure dhcp pool assigned to the remote lan to access your internal network.
I will also suggest to check the data sheets of different models so that you can check out the various features it provides/supports..
regds
