this post was submitted on 09 Nov 2026
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How do you isolate a printer in your homelab? (lemmy.zip)
submitted 9 hours ago by rearview@lemmy.zip to c/selfhosted@lemmy.world
34 comments fedilink hide all child comments
 

Hi all, I've gotten a Brother machine (DCP series) that can do wifi printing/scanning over their proprietary app. However, I'd like to lock it down from my network, because having it on the same LAN as my other devices and the ability to phone out to the internet seem like room for mischievious activities.

For context, I have OpenWRT on my router, and my clients can access the Brother using their iPrint&Scan app and AirPrint on wifi, as well as the traditional USB port. But I'm not good in networking. In my research, I drafted out the following solutions:

  1. Create a firewall rule to block the printer itself from making outbound requests. Seems simple, but I'm not sure if this can persist after IP changes or not.
  2. Create a VLAN for "IoT devices" that cannot send outbound requests to my normal VLAN nor the internet. Inspiration from this video, I'd need to manage a new SSID but it may come in handy for more IoT devices later.
  3. Hook the Brother up to a Raspberry Pi via USB, and install CUPS + SANE on the Pi. Assuming the Pi cannot "phone home" on behalf of the printer, this makes it a local-only "print+scan service" on my normal network and doesn't require an extra VLAN.

I'd like to ask: which solution above is best for "neutering" the Brother? Or are there any alternatives/details I might've missed? I'm not sure if blocking outbound requests this way is enough of a security hardening for an untrusted device, and if there are any usability issues I've overlooked so far.

Thanks for any advice, and please share any printer/scanner setup you have in your networks as well. So hopefully I can get more inspiration!

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[โ€“] lemmyvore@feddit.nl 5 points 9 hours ago* (last edited 8 hours ago) (2 children)

If it's a networked printer it needs to be able to broadcast to the LAN if you want IPP to work โ€“ which you probably do, since it's well supported by all OS and lets you autodiscover the printer and print directly from most of your devices.

This means you can't isolate it fully from the LAN, so solution 2 is out.

Solution 1 is good if you can trust the thing not to change or disguise its MAC address. I've heard of devices that have a 3rd dynamic MAC in addition to the wifi and ethernet MACs, that they use to bypass such restrictions. ๐Ÿคช

In order to do (1) properly you should create a firewall zone specifically for the printer, and allow that zone access to LAN but deny access to WAN. Then associate that zone with either a wifi access point created specifically for the printer, or with a specific switch plug if connected via Ethernet. This way the printer can't bypass the restriction because it comes packaged with the only way it has of getting any connectivity.

However OpenWRT firewall zones also have issues with cross-zone broadcast, but can be bypassed I think by installing and using Avahi on the router. Don't quote me on that.

Solution 3 seems best if you want to fully isolate it as well as retain IPP capability. That's what I did with my printer, I connected it with USB to the server and I run CUPS + Avahi in a docker container that uses an ipvlan network to broadcast.

[โ€“] flueterflam@lemmy.world 5 points 8 hours ago* (last edited 8 hours ago)

Your comment about #2 is not true. VLANs can be fully isolated from other subnets on the LAN - sure. But they can also NOT be isolated. I have one fully isolated VLAN, and the rest are not isolated.

With a savvy user, you can also tehnically isolate VLANs form only specific other VLANs. I've never needed to do this, but know it's possible.

Edit: for reference, I looked up details and found a helpful link and example:

5. Firewall zones for VLANs

config zone
    option name 'lan'
    option input 'ACCEPT'
    option output 'ACCEPT'
    option forward 'ACCEPT'     <-- This line allows intra-zone (inter-subnet) routing
    list network 'lan'
    list network 'your_new_vlan' <-- Adding your new VLAN here stops it from being isolated
[โ€“] rearview@lemmy.zip 2 points 8 hours ago (1 children)

Damn, I didn't know devices do these dynamic MACs, but yeah it's not a trusted field to begin with.

By IPP autodiscovery, do you mean mDNS? If so, does the router needs to install avahi as well for single-network discovery to work? Or just the client?

Avahi on the router for multi VLAN discovery seem to be a nice idea, I'll look into it and maybe try to hook it up to solution 2. I've thought users could just manually input the IP addresses (and the non-tech users will just simply be onboarded by me anyways), but having it advertised by default may just be less of a hassle for them.

[โ€“] lemmyvore@feddit.nl 1 points 6 hours ago

IPP is a universal printer protocol aka "print anywhere". Some printers support it natively, some need some help from a PC. If that PC runs Linux the most likely method is to run CUPS and connect it to the printer over USB.

By IPP autodiscovery, do you mean mDNS? If so, does the router needs to install avahi as well for single-network discovery to work? Or just the client?

Yes the autodiscovery is done with mDNS, which on Linux is done with Avahi.

Typically Avahi is needed if you consume services over mDNS or provide them.

So the Linux clients need Avahi. But the router only needs Avahi if the printer is connected to it, or to propagate broadcasts across zones.

I've thought users could just manually input the IP addresses

You can, but it's really nice to have the printer available automagically (on any OS).

BTW one extra potential benefit of solution 3 might be that the "printer" would always appear to be present on the network and accept print jobs, even if the actual printer is off, because the Pi running the print server would actually be on. Otherwise if the printer itself is providing the connectivity and announcement it will not appear in the list when it's off. Whether you consider this a plus or not depends on how you handle your printers, I turn mine off when not in use, but some people let it go into powersaving mode so it's always ready to print.