Microsoft 365 VPN split tunnelling
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Enterprises have traditionally used VPNs to support secure remote experiences for their users. While core workloads remained on-premises, a VPN from the remote client routed through a datacenter on the corporate network was the primary method for remote users to access corporate resources. To safeguard these connections, enterprises build layers of network security solutions along the VPN paths. This security was built to protect internal infrastructure and to safeguard mobile browsing of external web sites by rerouting traffic into the VPN and then out through the on-premises Internet perimeter. VPNs, network perimeters, and associated security infrastructure were often purpose-built and scaled for a defined volume of traffic, typically with most connectivity being initiated from within the corporate network, and most of it staying within the internal network boundaries.
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−For quite some time, VPN models where all connections from the remote user device are routed back into the on-premises network (known as _forced tunneling_) were largely sustainable as long as the concurrent scale of remote users was modest and the traffic volumes traversing VPN were low. Some customers continued to use VPN force tunneling as the status quo even after their applications moved from inside the corporate perimeter to public SaaS clouds.
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+For quite some time, VPN models where all connections from the remote user device are routed back into the on-premises network (known as _forced tunneling_) were largely sustainable as long as the concurrent scale of remote users was modest and the traffic volumes traversing VPN were low. Some customers continued to use VPN force tunneling as the status quo even after their applications moved from inside the corporate perimeter to public SaaS clouds.
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−The use of forced tunneled VPNs for connecting to distributed and performance-sensitive cloud applications is suboptimal, but the negative effects have been accepted by some enterprises so as to maintain the security status quo. An example diagram of this scenario can be seen below:
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+The use of forced tunneled VPNs for connecting to distributed and performance-sensitive cloud applications is suboptimal, but the negative effects have been accepted by some enterprises so as to maintain the security status quo. An example diagram of this scenario can be seen here:
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_Figure 1: A traditional Forced Tunnel VPN solution._
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−This problem has been growing for many years, with many customers reporting a significant shift of network traffic patterns. Traffic that used to stay on premises now connects to external cloud endpoints. Many Microsoft customers report that previously, around 80% of their network traffic was to some internal source (represented by the dotted line in the above diagram). In 2020 that number decreased to around 20% or lower as they have shifted major workloads to the cloud. These trends aren't uncommon with other enterprises. Over time, as the cloud journey progresses, the above model becomes increasingly cumbersome and unsustainable, preventing an organization from being agile as they move into a cloud-first world.
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+This problem has been growing for many years, with many customers reporting a significant shift of network traffic patterns. Traffic that used to stay on premises now connects to external cloud endpoints. Many Microsoft customers report that previously, around 80% of their network traffic was to some internal source (represented by the dotted line in the preceding diagram). In 2020 that number decreased to around 20% or lower as they have shifted major workloads to the cloud. These trends aren't uncommon with other enterprises. Over time, as the cloud journey progresses, the above model becomes increasingly cumbersome and unsustainable, preventing an organization from being agile as they move into a cloud-first world.
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The worldwide COVID-19 crisis escalated this problem to require immediate remediation. The need to ensure employee safety generated unprecedented demands on enterprise IT to support work-from-home productivity at a massive scale, which is still true in the post-crisis era. Microsoft 365 is well positioned to help customers fulfill that demand, but high concurrency of users working from home generates a large volume of Microsoft 365 traffic which, if routed through forced tunnel VPN and on-premises network perimeters, causes rapid saturation and runs VPN infrastructure out of capacity. In this post-crisis reality, using VPN to access Microsoft 365 is no longer just a performance impediment, but a hard wall that not only impacts Microsoft 365 but critical business operations that still have to rely on the VPN to operate.
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Microsoft has been working closely with customers and the wider industry to provide effective, modern solutions to these problems from within our own services, and to align with industry best practice. [Connectivity principles](./microsoft-365-network-connectivity-principles.md) for the Microsoft 365 service have been designed to work efficiently for remote users while still allowing an organization to maintain security and control over their connectivity. These solutions can also be implemented quickly with limited work yet achieve a significant positive effect on the problems outlined above.
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−For customers who connect their remote worker devices to the corporate network or cloud infrastructure over VPN, Microsoft recommends that the key Microsoft 365 scenarios **Microsoft Teams**, **SharePoint Online**, and **Exchange Online** are routed over a _VPN split tunnel_ configuration. This becomes especially important as the first line strategy to facilitate continued employee productivity during large-scale work-from-home events such as the COVID-19 crisis.
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+For customers who connect their remote worker devices to the corporate network or cloud infrastructure over VPN, Microsoft recommends that the key Microsoft 365 scenarios **Microsoft Teams**, **SharePoint**, and **Exchange Online** are routed over a _VPN split tunnel_ configuration. This becomes especially important as the frontline strategy to facilitate continued employee productivity during large-scale work-from-home events such as the COVID-19 crisis.
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_Figure 2: A VPN split tunnel solution with defined Microsoft 365 exceptions sent directly to the service. All other traffic traverses the VPN tunnel regardless of destination._
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−The essence of this approach is to provide a simple method for enterprises to mitigate the risk of VPN infrastructure saturation and dramatically improve Microsoft 365 performance in the shortest timeframe possible. Configuring VPN clients to allow the most critical, high volume Microsoft 365 traffic to bypass the VPN tunnel achieves the following benefits:
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+The essence of this approach is to provide a method for enterprises to mitigate the risk of VPN infrastructure saturation and dramatically improve Microsoft 365 performance in the shortest timeframe possible. Configuring VPN clients to allow the most critical, high volume Microsoft 365 traffic to bypass the VPN tunnel achieves the following benefits:
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- Immediately mitigates the root cause of a majority of customer-reported performance and network capacity issues in enterprise VPN architectures impacting Microsoft 365 user experience
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− The recommended solution specifically targets Microsoft 365 service endpoints categorized as **Optimize** in the topic [Microsoft 365 URLs and IP address ranges](./urls-and-ip-address-ranges.md). Traffic to these endpoints is highly sensitive to latency and bandwidth throttling, and enabling it to bypass the VPN tunnel can dramatically improve the end-user experience as well as reduce the corporate network load. Microsoft 365 connections that do not constitute the majority of bandwidth or user experience footprint can continue to be routed through the VPN tunnel along with the rest of the Internet-bound traffic. For more information, see [The VPN split tunnel strategy](#the-vpn-split-tunnel-strategy).
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+ The recommended solution specifically targets Microsoft 365 service endpoints categorized as **Optimize** in the article [Microsoft 365 URLs and IP address ranges](./urls-and-ip-address-ranges.md). Traffic to these endpoints is highly sensitive to latency and bandwidth throttling, and enabling it to bypass the VPN tunnel can dramatically improve the end-user experience as well as reduce the corporate network load. Microsoft 365 connections that don't constitute the majority of bandwidth or user experience footprint can continue to be routed through the VPN tunnel along with the rest of the Internet-bound traffic. For more information, see [The VPN split tunnel strategy](#the-vpn-split-tunnel-strategy).
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- Can be configured, tested, and implemented rapidly by customers and with no additional infrastructure or application requirements
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For full implementation guidance, see [Implementing VPN split tunneling for Microsoft 365](microsoft-365-vpn-implement-split-tunnel.md).
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−For a step-by-step process to configure Microsoft 365 for remote workers, see [Set up your infrastructure for remote work](..\solutions\empower-people-to-work-remotely.md)
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+For a step-by-step process to configure Microsoft 365 for remote workers, see [Set up your infrastructure for remote work](..\solutions\empower-people-to-work-remotely.md).
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## The VPN split tunnel strategy
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−Traditional corporate networks are often designed to work securely for a pre-cloud world where most important data, services, applications are hosted on premises and are directly connected to the internal corporate network, as are the majority of users. Thus network infrastructure is built around these elements in that branch offices are connected to the head office via _Multiprotocol Label Switching (MPLS)_ networks, and remote users must connect to the corporate network over a VPN to access both on premises endpoints and the Internet. In this model, all traffic from remote users traverses the corporate network and is routed to the cloud service through a common egress point.
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+Traditional corporate networks are often designed to work securely for a precloud world where most important data, services, applications are hosted on premises and are directly connected to the internal corporate network, as are the majority of users. Thus network infrastructure is built around these elements in that branch offices are connected to the head office via _Multiprotocol Label Switching (MPLS)_ networks, and remote users must connect to the corporate network over a VPN to access both on premises endpoints and the Internet. In this model, all traffic from remote users traverses the corporate network and is routed to the cloud service through a common egress point.
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−_Figure 2: A common VPN solution for remote users where all traffic is forced back into the corporate network regardless of destination_
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+_Figure 2: A common VPN solution for remote users where all traffic is forced back into the corporate network regardless of destination._
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As organizations move data and applications to the cloud, this model has begun to become less effective as it quickly becomes cumbersome, expensive, and unscalable, significantly impacting network performance and efficiency of users and restricting the ability of the organization to adapt to changing needs. Numerous Microsoft customers have reported that a few years ago 80% of network traffic was to an internal destination, but in 2020 80% plus of traffic connects to an external cloud-based resource.
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−The COVID-19 crisis aggravated this problem to require immediate solutions for the vast majority of organizations. Many customers have found that the forced VPN model is not scalable or performant enough for 100% remote work scenarios such as that which this crisis has necessitated. Rapid solutions are required for these organizations to operate efficiently.
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+The COVID-19 crisis aggravated this problem to require immediate solutions for the vast majority of organizations. Many customers have found that the forced VPN model isn't scalable or performant enough for 100% remote work scenarios such as that which this crisis has necessitated. Rapid solutions are required for these organizations to operate efficiently.
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−For the Microsoft 365 service, Microsoft has designed the connectivity requirements for the service with this problem squarely in mind, where a focused, tightly controlled and relatively static set of service endpoints can be optimized very simply and quickly so as to deliver high performance for users accessing the service, and reducing the burden on the VPN infrastructure so it can be used by traffic that still requires it.
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+For the Microsoft 365 service, Microsoft has designed the connectivity requirements for the service with this problem squarely in mind, where a focused, tightly controlled and relatively static set of service endpoints can be optimized simply and quickly so as to deliver high performance for users accessing the service, and reducing the burden on the VPN infrastructure so it can be used by traffic that still requires it.
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Microsoft 365 categorizes the required endpoints for Microsoft 365 into three categories: **Optimize**, **Allow**, and **Default**. **Optimize** endpoints are our focus here and have the following characteristics:
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- Are Microsoft owned and managed endpoints, hosted on Microsoft infrastructure
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−- Are dedicated to core Microsoft 365 workloads such as Exchange Online, SharePoint Online, Skype for Business Online, and Microsoft Teams
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+- Are dedicated to core Microsoft 365 workloads such as Exchange Online, SharePoint, Skype for Business Online, and Microsoft Teams
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- Have IPs provided
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- Low rate of change and are expected to remain small in number (currently 20 IP subnets)
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- Are high volume and/or latency sensitive
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The Microsoft Security Team has published [Alternative ways for security professionals and IT to achieve modern security controls in today’s unique remote work scenarios](https://www.microsoft.com/security/blog/2020/03/26/alternative-security-professionals-it-achieve-modern-security-controls-todays-unique-remote-work-scenarios/), a blog post, that outlines key ways for security professionals and IT can achieve modern security controls in today's unique remote work scenarios. In addition, below are some of the common customer questions and answers on this subject.
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−### How do I stop users accessing other tenants I do not trust where they could exfiltrate data?
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+### How do I stop users accessing other tenants I don't trust where they could exfiltrate data?
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−The answer is a [feature called tenant restrictions](/azure/active-directory/manage-apps/tenant-restrictions). Authentication traffic isn't high volume nor especially latency sensitive so can be sent through the VPN solution to the on-premises proxy where the feature is applied. An allow list of trusted tenants is maintained here and if the client attempts to obtain a token to a tenant that isn't trusted, the proxy simply denies the request. If the tenant is trusted, then a token is accessible if the user has the right credentials and rights.
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+The answer is a [feature called tenant restrictions](/azure/active-directory/manage-apps/tenant-restrictions). Authentication traffic isn't high volume nor especially latency sensitive so can be sent through the VPN solution to the on-premises proxy where the feature is applied. An allowlist of trusted tenants is maintained here and if the client attempts to obtain a token to a tenant that isn't trusted, the proxy simply denies the request. If the tenant is trusted, then a token is accessible if the user has the right credentials and rights.
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−So even though a user can make a TCP/UDP connection to the Optimize marked endpoints above, without a valid token to access the tenant in question, they simply cannot log in and access/move any data.
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+So even though a user can make a TCP/UDP connection to the Optimize marked endpoints, without a valid token to access the tenant in question, they simply cannot log in and access/move any data.
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### Does this model allow access to consumer services such as personal OneDrive accounts?
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In addition to the tenant restrictions feature noted in Q1, [conditional access policies](/azure/active-directory/conditional-access/overview) can be applied to dynamically assess the risk of an authentication request and react appropriately. Microsoft recommends the [Zero Trust model](https://www.microsoft.com/security/zero-trust?rtc=1) is implemented over time and we can use Microsoft Entra Conditional Access policies to maintain control in a mobile and cloud-first world. Conditional access policies can be used to make a real-time decision on whether an authentication request is successful based on numerous factors such as:
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- Device, is the device known/trusted/Domain joined?
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−- IP – is the authentication request coming from a known corporate IP address? Or from a country/region we do not trust?
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+- IP – is the authentication request coming from a known corporate IP address? Or from a country/region we don't trust?
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- Application – Is the user authorized to use this application?
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We can then trigger policy such as approve, trigger MFA or block authentication based on these policies.
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### How do I protect against viruses and malware?
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−Again, Microsoft 365 provides protection for the Optimize marked endpoints in various layers in the service itself, [outlined in this document](/office365/Enterprise/office-365-malware-and-ransomware-protection). As noted, it's vastly more efficient to provide these security elements in the service itself rather than try to do it in line with devices that may not fully understand the protocols/traffic. By default, SharePoint Online [automatically scans file uploads](../security/office-365-security/anti-malware-protection-for-spo-odfb-teams-about.md) for known malware
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+Again, Microsoft 365 provides protection for the Optimize marked endpoints in various layers in the service itself, [outlined in this document](/office365/Enterprise/office-365-malware-and-ransomware-protection). As noted, it's vastly more efficient to provide these security elements in the service itself rather than try to do it in line with devices that may not fully understand the protocols/traffic. By default, SharePoint [automatically scans file uploads](../security/office-365-security/anti-malware-protection-for-spo-odfb-teams-about.md) for known malware
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For the Exchange endpoints listed above, [Exchange Online Protection](/office365/servicedescriptions/exchange-online-protection-service-description/exchange-online-protection-service-description) and [Microsoft Defender for Microsoft 365](/office365/servicedescriptions/office-365-advanced-threat-protection-service-description) do an excellent job of providing security of the traffic to the service.
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