Networking Routing Question (subnet)

I work in a manufacturing plant where all of the process equipment resides on its own subnet that hooks up to a CISCO router that pretty much no one has access to.

I want to create a subnet on the network using a router or a managed switch.

the subnet that i am currently working with is 10.31.67.X.

Am i able to create a subnet on this subnet without having access to the router that this subnet is a part of?
michael_krellAsked:
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Aaron TomoskySD-WAN SimplifiedCommented:
You can plugin a router and create a new LAN with the current subnet being your wan.setup the wan side of your router as if it was just another computer on the subnet.
Now there are some questions as to how you need it to work:
Do devices on the new LAN need to talk to devices on the old subnet? This is pretty easy and may just work out of the box
Do devices on the old subnet need to access devices on your new LAN? This is harder and requires you setup port forwarding and such on your new router.
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michael_krellAuthor Commented:
are you talking about setting up a router as a gateway using NAT?

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Aaron TomoskySD-WAN SimplifiedCommented:
Yes. Without access to the main router you can't create a new subnet and route between it. The only option I see is to use another router to double nat and create your own LAN.
If you can give the reasons for what you are doing and how you want it to work maybe I can give a better solution.
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michael_krellAuthor Commented:
so basically you are saying i should install a router(gateway) with the WAN IP of lets just say 10.31.67.101

Then i have my machines attached to the LAN side of the machine lets just say the devices are 172.33.33.31, 172.33.33.32, 172.33.33.33

so i should set up port forwarding on the router to forward certain ports to these IP's

like
331->172.33.33.31
332->172.33.33.32
333->172.33.33.33

does that  make sense? i have only done port forwarding with my home network when playing multiplayer games or something.

Is a gateway really just a router that has NAT turned on?
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Aaron TomoskySD-WAN SimplifiedCommented:
Sounds like you got it. With that setup if you are on a device on say 10.31.67.104 and you connect to 10.31.67.101:331 it will send you to port 331 on 172.33.33.31
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michael_krellAuthor Commented:
interesting. so the device at 172.33.33.31 will only get a connection at port 331?

What if i have multiple devices that only can use a specific port. like a PLC or something. Like if i have multiple devices that use port 331 to communicate.
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rfc1180Commented:
First I would check with your IT team, there is a reason why no one has access to the device; you might end up getting yourself into trouble. You could do more harm than good; many things could go wrong that would leave the network in a unusable state if you do not know what you are doing

>Am i able to create a subnet on this subnet without having access to the router that this subnet is a part of?

You can; however, I would work with the IT team or vendor that manages that router to work on a solution that will meet your requirement as NATing on the new subnet could result in double natting elsewhere and eventually lead into a management nightmare. If your new network needs to communication with any devices on the plant network, I would recommend that you trunk to the existing router or connect to a spare layer 3 interface to segment the network correctly.

Billy
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michael_krellAuthor Commented:
Thanks, but i am still trying to learn how this works.
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Aaron TomoskySD-WAN SimplifiedCommented:
You would need a device that does port mapping in addition to forwarding. Sometimes called port translating. For example you could set all three 331,332,333 to all forward to 331 on each ip.
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michael_krellAuthor Commented:
have you ever used DD-wrt firmware?

http://www.dd-wrt.com
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Aaron TomoskySD-WAN SimplifiedCommented:
All the time. On buffalo linksys and dlink boxes.
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michael_krellAuthor Commented:
cool. so i would assume that DD-WRT firmware would do port mapping like you mentioned?
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Aaron TomoskySD-WAN SimplifiedCommented:
Yes it can.
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michael_krellAuthor Commented:
sweet.
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
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