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I often read that you should put customer machines into a separate (testing) network like a DMZ.

Is a layer 3 device (switch/router + firewall) a good option for this? Since some ports need to be accessed across the developer and testing network. Is that common practice or is there a better solution?

Some layer 2 communication should be possible for exploring the devices. How can that be achived if networks are splitted on layer 3?

Thank you in advance

  • Please clarify what you have in mind regarding layer 2 communication for "exploring the devices". – Jeremy Gibbons Aug 14 '18 at 11:37
  • When using DCP protocol in order to discover devices (e.g. Siemens), layer 2 is needed. en.wikipedia.org/wiki/Discovery_and_Configuration_Protocol – nodna Aug 16 '18 at 7:35
  • if you really need to use such protocols than the discovering and discovered devices need to be in the same subnet. I would however encourage you to look carefully at why you would need to have an unmanaged decide discover managed devices, or vice versa. That sounds like a recipe for trouble from a security perspective. I would generally prefer to have all that done by devices I control, and then export the data to whoever needs it. – Jeremy Gibbons Aug 16 '18 at 11:38
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Customer machines are usually considered "unmanaged" by your IT, so you would want them to have access only to a limited set of resources they absolutely need to reach. To do that, you would indeed implement a DMZ, i.e. a network zone for which inbound and outbound traffic are limited to an approved list of flows.

That in turn requires a firewall-like device, though that may not always be enough, from a security perspective. In my environment, we do not provide direct access from an unmanaged device to any platforms, even if the devices are in a DMZ. The DMZ typically allows access to a Citrix farm or jump server of some sort, which then allows the users to do whatever they are supposed to be doing.

I would seriously reconsider any architecture requiring a third-party device to have layer 2 access to anything on your network, or vice versa, because you essentially give up on any control you might have between the two (yes, you could force the traffic through a transparent firewall or IPS, but it's going to be messy).

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