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I am faced with an issue right now working for a small rural WISP. We have roughly 250 wireless customers throughout our area using Ubiquiti radios. Our main fiber drop comes in from a larger ISP on which they provide us several public networks (a /30, a /27, a /24, and some others (including IPv6)). We currently have all of our customers NAT'd through a single public address (which is scary and cannot continue). My end goal is to have every customer radio with its own public address. Our current router is an Ubiquiti EdgeRouter Pro. (The radios are assumed to be running in router mode in this environment)

While exploring many options for a re-design of the network my boss posed a question to me which I simply cannot give a solid answer for.

"Why don't we just throw a switch on the edge of the network and assign the radio IPs statically?" [Thus eliminating the router]

Everything I have learned about networking screams that this is a bad idea. However, I can't give solid reasoning to him as to why it isn't. Any feedback is highly appreciated.

Edit: Our network is behind what appears to be an ISP provided router that we do not have access to. It takes the first IP address in the beginning of our provided ranges.

  • Will all the addresses be in the same network? Also, if you do need NAT, a switch will not work for that. – Ron Maupin Dec 13 '18 at 21:26
  • Most of the addresses will be in the /24 that has been given to us. However, some of the devices will be in the smaller networks (i.e. the /27) for other reasons. Edit: Correct, I am looking to eliminate NAT. I guess I need an explanation why a switch wouldn't work for that. – Kevin Helfert Dec 13 '18 at 21:29
  • Unless they are all in the same network, you would need to use multiple VLANs, so you are going to need a router (or layer-3 switch) somewhere because routers route between networks. Switches, even layer-3 switches, do not have NAT capabilities. NAT is very resource intensive, so routers that NAT usually have special hardware to deal with that, and switches simply do not have that. – Ron Maupin Dec 13 '18 at 21:37
  • Would you mind expanding on the multiple VLANs part? As far as I know, you can theoretically run multiple subnets through the same switch. However, I know this isn't recommended. – Kevin Helfert Dec 13 '18 at 21:49
  • You could, but the problem is that a router on a network will need to talk to a router on the same network. How are you intending to connect the switch on the other side of the client routers? You will need to connect to a router, and the router will need interfaces in each of the client networks. That is normally done with VLANs. The packets from the various networks will then need to be routed from the client networks to your ISP network. – Ron Maupin Dec 13 '18 at 21:54
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What you can do on your own network depends on how the ISP is passing you the networks.

Since the ISP seems to be terminating the network on its router, you will really just connect the networks to the clients at layer-2. Your switch(es) would have a separate VLAN for each network if you are getting a single trunk link from the ISP. If you are getting separate links for each network, then you still want to use VLANs on your switch. You would only use a single VLAN if the ISP is using a single link will all the packets on the same layer-2 broadcast domain.

You will also need to think about whether or not you want to allow the clients to communicate directly with each other. Many ISPs do not allow that. You could use Private VLANs to keep the clients from discovering or communicating at layer-2.

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