We want user from the newly acquired company (domain b.com) to be able to authenticate to our helpdesk system in domain a.com via Active Directory. We do not have a point-to-point VPN to the new location and we are not planning to have one. Both company use static IPs for Internet access.
In both domains, the DNS server is a Domain Controller. Any pointer on what port(s) I need to open/forward so that I can create a trust between the two domain so that new users can authenticate to our helpdesk system?