I have recently set up a connection to a remote site. The connection between the sites is done at the ISP level (ie, this is not a B2B tunnel on ISA). I'm fairly lightweight in the networking realm, so hopefully I can describe this correctly. I have added a network object containing the private IP range of the remote site, as well as a route in network rules of ISA. I have also created a rule in ISA to allow all traffic between the two networks, and disabled strict RPC filtering.
We want to establish DNS forwarding and a trust between our two domains. DNS forwarding appears to work correctly - I can see traffic flowing to/from our DNS servers, and FQDN pings resolve and respond on either network. However, any other traffic from their site to mine fails (http, RDP, etc.). Most importantly, the domain trust fails. They are unable to complete the trust wizard due to RPC connection errors ("The Local Security Authority is unable to obtain an RPC Connection to the domain controller"). I can complete the configuration on my domain controller to theirs, and traffic from me to them flows correctly.
This would seem to indicate ISA is blocking something, but if I set logging to be live in ISA and trace traffic inbound from their network, I don't see anything. This indicates to me a firewall or configuration issue on their side of things. Curiously, I don't see ping requests (that do flow through ISA), either.
Is there anything else I can check that may be misconfigured on my end? I'd hate to be pointing the finger at their network team and discover it was my issue all along.