SSL VPN Split Tunneling and Office 365
As we shift to a much larger remote workforce than ever before, additional strains are being placed on the remote access infrastructure of many organizations around the world.
Over the past several weeks we have seen organizations adapt quickly, and as it relates to APM, implement split tunneling configurations to specifically allow Office 365 traffic to egress a client's local interface instead of the corporate network via the VPN tunnel. Microsoft publishes their Office 365 endpoints (URLs & IPs) via an API but occasionally they make changes and keeping on top of those changes can be an administrative nightmare.
To make the ongoing maintenance of the Network Access Lists / split tunneling configuration as seamless as possible, I’ve adapted a Python script (see GitHubRepo) we commonly use for SSL Orchestrator deployments to fetch Office 365 endpoints and update one or more Network Access Lists. Used in conjunction with iCall, this script will periodically check for and apply updates to your Network Access List(s) without any administrative intervention, allowing you to focus on other mission critical tasks.
The script is maintained and documented in this GitHub repository: https://github.com/f5regan/o365-apm-split-tunnel
Microsoft has provided us with a statement concerning their recommendations for Office 365 and split tunneling:
"Microsoft recommends excluding traffic destined to key Office 365 services from the scope of VPN connection by configuring split tunneling using published IPv4 and IPv6 address ranges. For best performance and most efficient use of VPN capacity, traffic to these dedicated IP address ranges associated with Office 365 Exchange Online, SharePoint Online and Microsoft Teams (referred to as Optimize category in Microsoft documentation) should be routed directly, outside of the VPN tunnel. Please refer to Microsoft guidance for more detailed information about this recommendation."
Microsoft’s recommendations have been incorporated into the script published in the aforementioned GitHub repository. See the changelog for details.
In addition to considering how the steps in this article may relieve some strain on your organization’s remote access infrastructure, I’d highly recommend visiting How to optimize SSL VPN connections when BIG-IP is reaching 100% CPU for further guidance on optimizing SSL VPN connections.