I'm no expert so I hope I explain everything right.
Let me first say something about our configuration a little bit: we have 3 sites: one main (A) and to branch offices (B+C). All have diferent subnets: 192.168.10.0 (A), 192.168.20 (B) and 192.168.30.0 (C). On each of them we have a Cisco 878 router. A VPN connection is configured between these sites. At the mainsite (A) we have an ISA server. Behind it is a Cisco 877 router connected to the internet. At site A all traffic meant for the internet (browsing etc.) passes through the ISA server and the 877 router.
I was told, that it was not possible to route all networktraffic from e.g. a client at site B through the router on site B to the router at site A and from there to the ISA server onto the internet (in case client at site B is browsing the internet e.g.). They said it is only possible to route traffic for the different subnets, but all other traffic would go directly onto the internet from the router at site B or C. Other option was to block all traffic from the branch offices to the internet except for traffic between subnets. The only way to force a client to use the ISA server was by configure it as a proxyclient (which has drawbacks)
My question: is the person who installed it, telling me the correct story?