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> For most people, those things are synonymous. When talking about these things in a tech-savvy forum, you'd do well to separate the components (switch, WiFi A

> For most people, those things are synonymous. When talking about these things in a tech-savvy forum, you'd do well to separate the components (switch, WiFi AP, router) out, rather than thinking them as one indivisible unit. It helps for clarity of conversation and thinking. You have some misconceptions that might arise from this muddling you're doing. > The point is isolating devices from each other isn't what people need. They need their devices to accept commands from each other or their computer/phone. What they don't need is their devices to talk to half the Internet. When did I suggest isolating these devices from anything other than the Internet? The whole point of having a router tied into the various VLANs on your network is so that you can program the router to decide what off-subnet traffic goes where. If you want to have a fully-isolated VLAN, you can... but I never mentioned any isolation other than from Internet egress. > A reasonable device only talks to a handful of locations because you didn't ask it to do anything else. If you purchase devices that are hard-coded to talk to machines hosted on someone else's servers, and you don't want to reverse-engineer and take ongoing maintenance responsibility for the software running in those devices, then your only choice in the matter if the manufacturer chooses to "host" those servers in GCP, AWS, or similar is to prevent the devices from talking to the Internet at all. You might also review this conversation I had regarding the infeasibility of making a whitelist for typical devices and clients that demand Internet access: <https://news.ycombinator.com/item?id=42455401 https://news.ycombinator.com/item?id=42455401>

ndriscoll 2y ago
Right, I suppose I missed that you didn't mention full isolation. That was further upthread. In that case I suppose the point is that what's desirable as an end-state from a security perspective is that none of these devices access the Internet (ideally with a firewall rule enforcing that). In the usual home scenario where there is only 1 networking device, VLANs and subnets both seem to me like their main purpose would be to isolate clients from each other, which for mass-market purposes is currently counterproductive (as it basically makes cloud servers a requirement for non-experts). You could use them to make your firewall rules simpler, but then you need routing an multicast forwarding rules. What you really want is to get to a place where your firewall says that your PC/phone can access the Internet and nothing else can. Basically the infeasibility of making a whitelist for typical devices is exactly the problem to solve/issue to regulate.
- simoncion 2y ago
  > That was further upthread. No, that was in all of my replies. I've been consistent about this. > You could use [VLANs] to make your firewall rules simpler, but then you need routing an multicast forwarding rules. If you're not going to be running your multicast software on a machine that is wired in to all relevant VLANs (like your edge router), then yeah, if you need cross-VLAN multicast you would need to have multicast forwarding set up on such a machine. You'd need to do the same for broadcast, which is "just" all-nodes multicast. > In the usual home scenario where there is only 1 networking device, VLANs and subnets both seem to me like their main purpose would be to isolate clients from each other... Then you're confused about how VLANs and subnetting are typically used. I can think of three ways to do what I think you're envisioning. 1) Use the "client isolation" feature of WiFi APs. I think this uses something OTHER than VLANs, given that clients get allocated IP addresses from the same subnet as each other. 2) Create a subnet and VLAN per client and program your router to not permit traffic originating from these special subnets to go anywhere other than direct to the router or out to the Internet. 3) Have one or more fairly fancy switches that are programmed to only permit packets to flow from each client port to the router port. (I'm pretty sure that this is conceptually what the often-present WiFi "client isolation" feature is.) I know that you cannot prevent clients in the same subnet and VLAN from talking to one another unless you have direct intervention by a wireless or wired switch. This is because clients in the same subnet trying to talk to each other don't bother talking to the router and just use ARP (or ND) to find their conversation partners. I'm not CERTAIN, but I think that if you try to have clients in the same subnet, but on different VLANs, it will work poorly (or not at all) because the router will have a hard time with route selection for incoming traffic, as well as traffic originating on the router to the client subnet.

ndriscoll 2y ago

Right, I suppose I missed that you didn't mention full isolation. That was further upthread. In that case I suppose the point is that what's desirable as an end-state from a security perspective is that none of these devices access the Internet (ideally with a firewall rule enforcing that). In the usual home scenario where there is only 1 networking device, VLANs and subnets both seem to me like their main purpose would be to isolate clients from each other, which for mass-market purposes is currently counterproductive (as it basically makes cloud servers a requirement for non-experts). You could use them to make your firewall rules simpler, but then you need routing an multicast forwarding rules. What you really want is to get to a place where your firewall says that your PC/phone can access the Internet and nothing else can. Basically the infeasibility of making a whitelist for typical devices is exactly the problem to solve/issue to regulate.

simoncion 2y ago
> That was further upthread. No, that was in all of my replies. I've been consistent about this. > You could use [VLANs] to make your firewall rules simpler, but then you need routing an multicast forwarding rules. If you're not going to be running your multicast software on a machine that is wired in to all relevant VLANs (like your edge router), then yeah, if you need cross-VLAN multicast you would need to have multicast forwarding set up on such a machine. You'd need to do the same for broadcast, which is "just" all-nodes multicast. > In the usual home scenario where there is only 1 networking device, VLANs and subnets both seem to me like their main purpose would be to isolate clients from each other... Then you're confused about how VLANs and subnetting are typically used. I can think of three ways to do what I think you're envisioning. 1) Use the "client isolation" feature of WiFi APs. I think this uses something OTHER than VLANs, given that clients get allocated IP addresses from the same subnet as each other. 2) Create a subnet and VLAN per client and program your router to not permit traffic originating from these special subnets to go anywhere other than direct to the router or out to the Internet. 3) Have one or more fairly fancy switches that are programmed to only permit packets to flow from each client port to the router port. (I'm pretty sure that this is conceptually what the often-present WiFi "client isolation" feature is.) I know that you cannot prevent clients in the same subnet and VLAN from talking to one another unless you have direct intervention by a wireless or wired switch. This is because clients in the same subnet trying to talk to each other don't bother talking to the router and just use ARP (or ND) to find their conversation partners. I'm not CERTAIN, but I think that if you try to have clients in the same subnet, but on different VLANs, it will work poorly (or not at all) because the router will have a hard time with route selection for incoming traffic, as well as traffic originating on the router to the client subnet.