Whitelisting Exchange 365 IP ranges

Posted on 2013-12-18
Last Modified: 2014-01-02
For accessing exchange 365, there is a whole list of IPs that needs to be bypassed via firewall:

But still microsoft maintains that the IPs are dynamic and subject to change and we need to subscribe to an RSS feed to keep track of these IP changes.

Is there an easier way out to let our Firewall / proxy access office 365 un-hindred? microsoft suggests to configure firewall rules based on DNS rather than IP but Cisco's ASA series doesn't support that.

Also, any other security precautions we need to consider while opening up these access IPs/ ports to microsoft DCs?
Question by:fahim
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LVL 24

Expert Comment

by:Mohammed Hamada
ID: 39728555
You can ask Microsoft directly to provide you with CIDR for their networks! and for further security you can setup an IDS or if you have it already on your ASA Firewall then you can configure it.

The IDS is very effective and secure but you may want to do some alterations to change some things in relatation with how restricted is the policy.

Author Comment

ID: 39735447
Microsoft has indeed provided the CIDRs. The issue is that there are IP ranges of /16, /24 ranges and that's about 15 of them. Moreover, Microsoft recommends to open outbound ports 80 as well as 443 to all of these hundreds of thousands of IPs ( ). With no IPS in the middle, how safe would be this outbound access? What are the threats?
LVL 24

Accepted Solution

Mohammed Hamada earned 500 total points
ID: 39735546
For an outbound connection I don't think there would be threats if they were owned by Microsoft.

I mean you said those IPs are dynamic which means they'll change but probably in the scope of Microsoft's CIDR! right?

If so then I don't think there will be a risk for an outbound connection since you know the ranges that connection is going to! and as I said for more security you can setup your IDS to filter all packets.
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Author Comment

ID: 39735765
If it's an https (443) connection, what would be the benefit of an IDS?
LVL 24

Expert Comment

by:Mohammed Hamada
ID: 39735870
The IDS will work for HTTP only, but for HTTPS If the CIDRs of Microsoft doesn't change then I don't think you will need to worry unless Microsoft's infrastructure gets infected.

Author Comment

ID: 39737983 related query was also that Microsoft suggests to configure firewall rules based on DNS rather than IP but Cisco's ASA series doesn't support that....

This becomes an administrative issue to keep track of RSS feeds and knowing which all IPs to poke holes for within the firewall. Any other better mechanism around?
LVL 24

Expert Comment

by:Mohammed Hamada
ID: 39738134
Then I'd suggest an open source firewall that would work and wouldn't cost you much at the same time.

I'm using Pfsense firewall, I have already set it up in multiple customers based infrastructure and it's doing a great job. it has been up for a really long time.

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