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In the firewall policy, how can we add all of Microsoft's ip addresses as trusted?

The firewall is blocking rundll.exe from accessing external sites that are not listed as trusted. We don't want to allow rundll.exe to access all external sites, just the Microsoft sites. I've already added the following sites as trusted:

microsoft.com

www.microsoft.com

office.microsoft.com

outlook.office365.com

www.office.com

portal.office.com

By adding the above as trusted sites in the LAN section of the firewall policy, many of the problems we had with Outlook and Office 365 disappeared. However, just yesterday we discovered some more Microsoft ip addresses that Outlook was trying to access via rundll.exe but were being blocked. I don't want to have to add individual ip addresses every time Outlook is redirected to a different Microsoft server. How can we set up the firewall to always allow legitimate traffic to any known Microsoft server?

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0 QC over 9 years ago

Hello DianaGallegos,

first of all, you should never add and mark external addresses to the LAN section. Trusted allows all traffic, outgoing and incoming (don't forget that addresses can be spoofed).

You should add the addresses (and if feasible ports) in an application rule (though rundll isn't an application, the firewall can't know what rundll is running so you can't tell whether this is legitimate traffic). Wonder why Microsoft is using a plethora of addresses but anyway you could use IP address with wildcards or subnet mask, e.g. 132.245.226.0 (255.255..255.0). Likely all these belong to Microsoft but there might not only known Microsoft servers be behind them.

You are configuring a client firewall which deliberately doesn't use host or domain names in its rules as it could be subverted by a rogue DNS.

Christian
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