Is it working fine to have IOT on a different vlan, lot of IOT use weird protocol ( mdns, multicast etc ... ) that are not friendly with vlan? I know that some people have issues for example with the Chromecast being seperated since it needs internet but also be able to communicate with your phone on a different vlan.
Multicast doesn't cross between IP _subnets_ - it doesn't necessarily have to do with VLANs, strictly speaking. But yes, in practice
VLAN←→subnet
Make sure IGMP is enabled. Devices join IGMP groups to announce they want to receive mDNS
- IGMP snooping
- IGMP proxying (if offered)
Depending on your router you might find helpful options like:
- mDNS reflector
- mDNS repeater
- any mDNS + description of multiple networks (Unifi)
tcpdump -i <interface> host 224.0.0.251 or port 5353 -A
Like others mentioned, Avahi is solid but the multicast reflection/repeater/relay must run on the device routing between the VLANS in question.
Disclaimer: Deployed and networked thousands of Chromecast at several hotel chains and their wildly variable enterprise networks. Wrote my own mDNS repeater-as-a-packet-rewriter to fine-tune TXT records.
IoT VLAN indeed can be annoying. It's getting better as a lot of the more "prosumer" grade routers are supporting it. I use Sonos at home too, which means I had to deploy this into a VM to bridge the VLANs: https://github.com/alsmith/multicast-relay.
There are some funny (?) things that turn up too, like learning the Roku remote iOS app "discovers" devices by opening a TCP connection to every address in parallel on its local /24 (!!!). It sends out and receives mDNS packets that would tell it exactly where they are, but they are ignored by the app.
My IoT VLAN is one way only (main VLAN can talk to it, and it can talk back BUT it cannot talk to any other VLAN on its own accord). No issues with mDNS or multicast. I redirect all DNS request as well to nextDNS with masquerading. I have probably 30 devices on it? Zero issues with home assistant and HomeKit
Yeah, avahi will help you out quite a bit there, but I personally pick my IOT devices to where they will not have requirements like that. I'm pretty #nocloud with anything I put in my home, so the majority of IOT devices I have go on the null routed VLAN and are perfectly happy.
Assuming you have a linux machine connected to both networks, Avahi can reflect/forward mDNS multicast traffic, so you can have your chromecasts on a separate network and be discoverable by devices on a different one.
