We have 2 locations: primary and secondary(DR).
Exchange servers are located in the secondary(DR) location.
site to site vpn tunnel between primary location and secondary location.
All is well, users are able to get their emails UNTIL we turn off our isp and switch to our backup ISP through a different firewall.
Internal dns still trying to resolve mail.companyname.com to internal ip, but is unable to since the vpn tunnel is broken. RPC over http or outlook anywhere is not establishing connection to external ip of mail.companyname.com thus we all lose connection to exchange.
When i manually put in external dns server in my PC (for example: 4.2.2.2), mail.companyname.com resolves and outlook works, but then i am unable to get to my internal devices because now PC is forced to look to external dns.
any idea how i can fix this issue? I want outlook to work when i disconnect primary isp and vpn tunnel and force traffic to go through secondary isp.