I'm sorry for this basic question, but I'm stuck. I'm looking for some networking equipment that allows me to route WAN traffic (internet) to a client on a local LAN based on TCP/UDP port. That is, basically what you can do with a simple ISP router. The problem is, I have about 30 clients and can't figure out if a layer 3 switch (48 ports) can manage this NAT function or if I need a switch (layer 2) in combination with something else. I'd rather get something professional rather than a wireless ISP router which needs a reboot twice a month.


What the situation looks like more specifically is:

I have one network cable connected to the ISP. Then I have about 30 clients of different kinds (mostly HVAC automation devices) that speak different protocols, all over TCP/IP and on different TCP ports. What I need to do is expose these one way or another to the internet, so that I can access the clients externally. That is, using one IP address I want to connect to one of those 30 clients based on TCP port.

As soon as I'm able to understand the basic principles about this, and what kind of gear I need (switch, firewall, etc.) I will need to take another step to understand the security aspect in this. I obviously don't want anyone to be able to access my automation stuff.

  • What you are trying to do is source NAT (or SNAT). There are L3 switches that offer this kind of functionality but not all do. In any case, you are better off configuring your gateway router to do WAN-LAN SNAT, and not your L3 switch. A more precises answer would require you to ask a more precise question. – bjanssen Jun 17 '14 at 5:20
  • Thanks for the reply and I'm sorry for being vague. I will try to express the situation more clearly. Since I can't make new lines in a comment, I will update the original post instead. – user2408193 Jun 17 '14 at 5:46
  • That’s how it should be done anyway. :) Even if it’s consumer-grade hardware, it can be rock stable with OpenWrt or friends. I reboot my router (WNDR3700, OpenWrt) only when making severe network changes. Typical uptime is up to 180 days. – Daniel B Jun 17 '14 at 7:30
  • Isn't this actually PAT (port address translation), which multiplexes a single WAN ip onto n internal clients? – sinni800 Jun 17 '14 at 9:09

there are two ways to do this i guess:

1)Use NAT - this will transalte an internal to external IP which will allow you to accomplish what you are after.

2)If the traffic is inbound only - you can use port triggering or port forwarding. This will take all inbound data and sent traffic on port x to internal IP y, or port z to ip a.. and so on.

Hopefully one of these will get you up and running in the way you need.

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