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I think am looking for a way to reliably communicate with devices connected to the network with "wrong" configurations.


Our company sells products that can have their network settings changed. When a product is sent back to us for repair, it is typically configured for a completely different network, so we can't access it directly.

Our office has multiple users connected to a main switch, the same switch that arbitrary returned devices are connected to for repairs. This diagram shows a simplified architecture: Office Architecture

Currently, the way I would interact with this unit is to change my IP address to the same subnet - I could change my IP to 10.196.212.117/25 so I can interact with the product. However, returned products could be configured to anything - even the same IP address as an existing device on the network.

Instead of changing my IP all the time, is there a device (or RPI setup) that could make connection to a returned product with random configuration easy? For example, having a designated IP like 192.168.1.20 that will always "tunnel" traffic to the device connected to the switch interface f0/30 would be an ideal solution.

2 Answers 2

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The DUT (device-under-test) should ALWAYS be in it's own network. You have no idea what sort of things could be on the device sent back to you.

It will be difficult to talk to a device when you know nothing at all about it's network setup. With it sitting in an isolated network, it's possible to watch for traffic coming from it - ARP looking for it's gateway, broadcast traffic with it's IP, etc. That's looking for a needle in a haystack.

The best way to address this is with a layer-2 device discovery protocol. You'd have to add that to your product(s). LLDP comes to mind, but there are many proprietary methods.

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  • Thanks @Ricky for your warning about network separation - I think you're right. Also, separating the network will make finding the needle in the haystack will be easier. For example lets say there is only a single DUT connected - In implementing your idea, would this look like an RPi or Linux host observing the LLDP frames, and changing its Gateway address to match the device? (While keeping another network interface constant)
    – nickolaij
    Sep 3, 2023 at 21:13
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You should connect that device to an extra network segment/VLAN and move the necessary configuration from your workstation to the router connecting that VLAN. However, there's no magical way to make it work without adjusting the router's config each time, and there's no easy way to connect duplicate IP addresses.

The proper way would be to implement DHCP and use a dynamic IP configuration that adjusts to the network it's plugged into.

If DHCP isn't possible you could capture and analyze outgoing traffic from a (newly) connected device. Provided that those devices are very similar, you could even automate the analysis as a device would try to ARP its gateway and possibly DNS server, or send broadcast advertisements. You could also store discovered information in a database under the device's MAC address to speed up future config changes.

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  • DHCP is not possible. How would I go about implementing automated analysis of the ARP requests? (I apologize I'm new to networking)
    – nickolaij
    Sep 3, 2023 at 21:15

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