Identical VLANs with identical DHCP, is this possible?

[Green1690]

Hello Friends! I am wondering if the following architecture is possible with RouterOS.

I purchased 2x CRS305 switches to use to interface with some specialized industrial equipment. The downside with this equipment is that every piece has a hard-coded and unchangeable static IP address.

The goal is to have 3 independent VLANS, that are all configured for a subnet of 192.168.1.0/24, and DHCP for the client device to connect to. The VLANs will use port assignments so that the end result is 3 independent networks with no cross-talk between them, and they are trunked over a single fiber line to the other switch.

In layman’s terms, an equipment operator would plug their human-machine interface into SFP1 on the terminal switch, get a DHCP address, and be able to contact the server on SFP1 on the other side, and only that server.

My question is: how would I set up DHCP for the clients on the terminal switch? Would I set up 1 server and a relay for each VLAN? Or should I set up multiple DHCP servers? Technically, they could all pull from the same pool, since the IP distributed only needs to be routable on the subnet. (in other words, I don’t care if the human machine interface plugged in to SFP1 gets 192.168.0.3 and the HMI plugged into SFP2 gets 192.168.0.4).

Thanks for your help!

[holvoetn]

This is very well possible and already has been discussed around here a couple of times.

I'll try to find back a reference, suggest you do the same

[holvoetn]

Here is one

Route to interface, interfaces have same subnets

Hi, I need to connect 4 “industry machines”. Everyone use same subnets 192.168.0.0, network device inside macihne have same static IP and I’cant change them. Inside machine is switch whitch networking two internal devices (192.168.0.2, 192.168.0.3) and some device for managing machine. Managing this machine means connect them with TCP on IP 192.168.0.2 port 1234 and push some data. (Which is step one. Step two i the same on port 1235). My idea is to make connection to 192.168.2.2 (ether1/LAN …

[CGGXANNX]

There are even two topics about this in the Latest rtfum topics - MikroTik community forum that @BartoszP has tagged, because how often this scenario came up weekly on the forum .

One of the topics is even written as a guide:

Quick Guide: Bidirectional 1:1 NAT (SNAT, DNAT) Setup w/ working example

Intro Setting up bidirectional 1:1 NAT in RouterOS allows you to create static mappings between external and internal IP addresses. This configuration is useful when you need multiple internal (LAN) devices to be accessible via specific external (WAN) IPs. There is a special twist though, since in this particular setup all internal devices are using the same IP address (this was a mandatory requirements since we were not able to change the IP addresses on any of those devices). This quick guid…

And here is a topic with more details:

1:1 NAT / DNAT configuration help

Hello, we are using "CCR2004-16G-2S+” and need to configure 1:1 NAT (bi-directional) from 8x internal device to 8x external IP address. +-------------------------------+ | Linux Edge Device (Client) | | IP: 172.29.10.10/24 | +---------------+---------------+ | | +---------------------+--------------------------+ | | | | | | | | 172.29.10.10…

[holvoetn]

Couldn't find them right away via smartphone.
Thanks for adding those.

[jaclaz]

Also related:

Port based Routing to 2 identical IP

Hello, I have 2 standalone machines that are identical and use the same IP addresses. They are currently not integrated in any network. I would like to access these 2 machines (VNC) from a remote PC, but I can’t change their IP addresses. Is it possible to make this setup work using NAT based on physical port / interface? Or a port forwarding based on physical port may also work? Here a schema of the configuration: [Screenshot_3.png]

[Green1690]

thanks @jaclaz @CGGXANNX and holvoetn (can’t tag more than 2 users!) , I guess I wasn’t hitting the right keywords in my searching to find these posts. I’ll read up on these and see if I can’t figure it out from there.

Much appreciated!

[Buckeye]

@Green1690

In layman’s terms, an equipment operator would plug their human-machine interface into SFP1 on the terminal switch, get a DHCP address, and be able to contact the server on SFP1 on the other side, and only that server.

How many "human machine interfaces" are being used? If it is only a few, and they are only used for that specific purpose, you could just assign a unique static address in 192.168.1.0/24 to each "human machine interface" and then create 3 distinct vlans with no routing, with access ports for the "NET1", "NET2" and "NET3" vlans. This would essentially be like three long cables, one from each "specialized industrial equipment" server to a remote patch panel, with the ports labelled. Then you would connect the "human-machine interface" device into the patch panel port associated with the device you want to connect to at the other end.

It doesn't solve the stated requirements (that the ip addresses are obtained via dhcp), but it is a much "simpler" solution if the requirement for dhcp is not a "real requirement".