Ethernet IP Address Scheme

What is a good ethernet ip address scheme to use when starting a new plant which will have 7 lines and each line needs tobe its own seperate network but there will be one system now that needs to talk to all lines and in the future some of the lines may talk to each other but they will never be one network for all equipment.

I want to start out right with the addresses and not have to re ip equipment after startup?

Go private network, class A or B.

For A, 10.x.y.z, all subnetted to 255.0.0.0 or 255.255.0.0.
Make the 'y' the machine number, and the 'z' the device index on the machine. The 'x' can be the plant number if you like (and have multiple).

For class A, you have 10.0.0.0 to 10.255.255.255 available in your IP Domain.
For class B, you have 172.16.0.0 to 173.31.255.255 available in your IP Domain.

Both of those are non-routable through the Public Internet.

Bob

bob routable through the public internet? Will this cause problems with remote access?

We want to be able to vpn into the machines from outside? Internet?

Rdrast - Is there any reason you would use /16 over /24 in particular? I always use /24 to cut down on the broadcast traffic and crosstalk between machines.
Just curious really as I'm somewhat new to this.

The Plc Kid said:

Bob

bob routable through the public internet? Will this cause problems with remote access?

We want to be able to vpn into the machines from outside? Internet?

Click to expand...

Easiest way would be to setup a computer w/ 2 nic's, one connected to your internet facing network and one to the non-routable network. You would then VPN through this computer.

Is there any reason you would use /16 over /24 in particular? I always use /24 to cut down on the broadcast traffic and crosstalk between machines

16 over 24? What does that mean?

Sorry, /16 is another way of saying 255.255.0.0, and /24 is another way of saying 255.255.255.0 , I was just using the CIDR notation.

The only reason I don't limit within a site, is it doesn't matter if you have a sparse population, and it gives plenty of room to expand, while keeping machines grouped together.

Here, we use the second octet for plant number, the third for cost center, then the fourth for IP devices on machines.


@ PLC Kid : No, it causes no problems, as if you want remote access, you will VPN in anyway. By using one of the reserved address ranges however, Public Routers will NOT pass traffic, except as masked through a VPN or other tunnel route.

Go outside of the reserved ranges, and you A) Become Public, and B) must obtain a static IP range, which is not exactly cheap.

Bob

Why would i use class A over B or B over A. What is the main difference i should be thinking of when choosing between the two?

It is all about the number of Hosts (PLCs, HMIs, PCs) that you can have on a subnet, ie that can easily share data (read on for a description of subnets). Actually the whole class system is now out of date, it was far too inflexible in the way you select how much of the IP address to use to indicate Network and how much to indicate Host. You have seen that an IP4 address is made up of four octets eg 192.168.0.1. The way that is written is for our benefit, a network device actually sees it in binary as a list of 32 1s and 0s (four lots of eight bits, hence octet). Part of the address identifies the Network address and part identifies the address of the Host within the network. Like part of your telephone number gives the Area and part gives the Number within that Area. The more bits you use in an IP address to represent the Area the more Areas you can have but the fewer bits are left to identify individual Telephones in that Area.

So if you can use some of the IP address to represent Network and some to represent Host, you need some way to tell a network device which is which. This is where the Subnet Mask comes in, it uses a 1 to say that this part of the address is Network and a 0 to say the it is Host. so when you see 255.255.255.0, that is 1111111111111111111111100000000 in binary so you can see that a lot of the address represents Network but only a quarter represents Host, so you could have a lot of networks 16581375 with 255 Hosts on each Network (these numbers aren't right as some IP address have specific uses and cannot be used by Networks or Hosts).

Rather than me spend hours explaining this, go here and follow the complete course. Or Google 'subnet mask'.

In practice the choice between Class A or B doesn't matter you won't be getting anywhere near the limit of the number of Hosts in either case. Class A allows for 16,777,214 Hosts and Class B 65,534 Hosts, I am guessing that won't have that many PLCs to be concerned. I suppose that you could reach the limit of 254 Hosts for a Class C system but that would still be 36 device on each of your 7 lines. (7*36 = 252, max Class C is 254).

Bryan

Thanks for thin info. One more small question why are the hosts limited to 254? I thought it should be 256 total 0-255 so how is it 254? Is there one reserved for something?

I know x.x.x.255 is reserved for broadcast messages, but can't remember what x.x.x.0 is used for, but it is also reserved. Therefore only 254 of 256 (0-255) can be used.

The Plc Kid said:

Thanks for thin info. One more small question why are the hosts limited to 254? I thought it should be 256 total 0-255 so how is it 254? Is there one reserved for something?

Click to expand...

Usually you reserve 1 host for your default gateway and 1 address is the broadcast address

Back to the topic at hand, another thing that I didn't see mentioned, was to use a managed switch and create a Vlan for each line. It's a solution that will probably give you more flexibility, security, and control in the long run.

Each line will have stratix 8300 managed switches. and will connect to a cisco catalyst central switch. With a windows server 2008 r2.

I also have to find a way to give oems remote access to their line and not be albe to connect to any others as well as give maint/engineering remote access to all equipment.

VPN... simplest 3 letter acronym for this problem.