Richard Hicks has a great blog entry on this at so I won’t go into detail on the overall process. However, there are a couple of gotchas to be aware of, although these aren’t anything to do with TMG itself.

First, as you are probably moving from Server 2003 to Server 2008, the number of trusted commercial Certificate Authorities has been trimmed down – if you are importing an SSL certificate from one of the less well known authorities,  the root CA may not be trusted. The import will succeed, TMG will allow you to specify the cert in publishing rules, but the results can then be unpredictable. Note that if you do have to add the root CA to your trusted CA store after TMG has been configured to use the SSL certificate, it is worth rebooting the server – without a reboot, TMG registers no errors, but client devices may display untrusted cert errors.

Therefore, when you import SSL certificates onto the TMG server, verify three things:

  • The certificate is in the local machine’s Personal store
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  • The certificate has a matching private key
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  • The certificate path is fully validated
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Second, if you are planning a TMG to ISA migration, you will probably be moving to new hardware, as it will have to be a side by side migration. This obviously means that the MAC addresses of all your NIC’s are going to change, so talk to your networking guys – at the very least, you will probably need ARP tables on the relevant routers/switches to be flushed at the point you actually swap cables, otherwise you  may end up with the situation I was in, where TMG was up and running with no errors, but no traffic for publishing rules on addresses other than the native IP address of the external NIC ever hit TMG, which was definitely a head scratcher for a while :).