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Microsoft — and Ars — advise split-tunnel VPNs to minimize coronavirus woes, Ars Technica

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Microsoft — and Ars — advise split-tunnel VPNs to minimize coronavirus woes, Ars Technica

      vpn is the antonym of cdn –

             

Don’t waste limited local bandwidth on VPNing remote users’ Office traffic.

      

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                                                                 The traditional office VPN routes not just internal office traffic, but all traffic — including internet traffic — across an established VPN.                                                         

                                                  Jim Salter                                                                   

                                    

                                                                 In a split tunnel (selectively routed) VPN setup, intraoffice traffic goes over the VPN, but some or all internet-targeted traffic is allowed to proceed outside the VPN.                                                         

                                                  Jim Salter                                                      When SARS hit its peak, remote work was not yet practical enough for quarantine efforts to affect office networks much. With the coronavirus, though, most of the toolset needed to work from home or the road is available — but many office networks are having difficulty handling the sudden increase in scale.
    Internet scale versus VPN scale There’s not much you can do about a WAN (Wide Area Network) connection that isn’t robust enough to handle traffic from remote workers to internal infrastructure such as file servers and application servers. But much of a typical company’s infrastructure isn’t onsite at all anymore — it’s more likely to be hosted in the cloud, behind its own set of protective firewalls and filters.

    Traditionally, most office VPNs are set up to route not just office traffic, but (all) traffic — including Internet-destined traffic — across the user’s VPN tunnel. For most sites, that means paying a double penalty — or worse — for all Internet traffic from VPN-connected users. Each HTTPS request and its subsequent response must hit both the upload and download side of the office’s WAN twice. This is bad enough with a symmetric WAN — eg, a 728 Mbps fiber link — but it’s beyond punishing for an asymmetric WAN, such as a Mbps-down / 90 Mbps-up coaxial link.

    The idea behind globally routed VPN tunnels is to allow an office firewall to inspect and monitor all traffic. Modern Internet traffic is almost entirely end-to-end encrypted, however, which makes such inspection of dubious value. There’s little reason to route Office 365 traffic through a typical office’s local Internet connection, instead of allowing it to flow directly from remote worker to the cloud.

    Routing as much as possible directly to the Internet

    We generally advise routing

      only

      office-bound traffic over an office VPN and allowing all Internet traffic to proceed directly to its destination — this can easily reduce VPN traffic by an order of magnitude or more, and the router-level filtering and monitoring in most offices isn’t particularly useful in the first place.

    Doing things this way is simple — the network administrator disables global routing in their VPN configurations and only routes the office’s subnet (s across the tunnel. The details vary by VPN implementation, but in Cisco VPN clients, for example, it’s a simple checkbox to be ticked on or off.

                                                                 This list of service URLs can also be fetched with a Powershell script , but the simple table helps visualize things.                                                         

                                                  Microsoft                                                      
                

                                    

                                                                 Note that this IP range is subnet to change — fresh copies can be gotten using this Powershell

    script .                                                         

                                                  Microsoft                                   

                      Somewhat more paranoid (or Orwellian) environments might not be willing to relinquish (all) control over Internet-bound traffic, however, preferring instead to only enable known-safe services — such as Office .

    This raises the question, how do

    you identify Office 500 – bound traffic? Microsoft provides an API for identifying Microsoft service endpoints, which can be queried via a Powershell

  • script . Although the company recommends setting up a dynamic, regular update procedure to use the API to harvest all necessary endpoints, Microsoft has also provided a simple list that’s correct for now.

    IPv6, unfortunately, gets its usual “eh, maybe later” treatment — Microsoft advises that IPv6 endpoints can simply be ignored and notes that its services “will currently operate successfully on IPv4 only, but not the other way around.”

             Listing image by CDC

                                                               

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