rslinx and ip addressing

stu · Jun 25, 2009

i guys another question for you, i have quite a few allen bradley plc on our machine's and they all have different ip addresss what i am asking is can i set up moer then one ip address on the laptop so i can talk to the plc,
the laptop ip is = 192.168.1.254
1 machine ip is = 192.168.0.20
2 " " " " = 192.168.0 101
3 " " " = 192.168. 1 .50
4" " " " = 192. 168.1.80

CAN I TALK TO THE PLCS WITHOUT CHANGING THE IP ON THE LAPTOP ALL THE TIME.

jonnies · Jun 25, 2009

It depends on your subnet mask and the subnet mask of all the machines. In the examples you gave all the IP's begin with 192.168. If this is the case, the most straightforward way is to have a subnet of 255.255.0.0 for every device including your laptop. That would put everything on one single network, and you would not have to change your IP.

daba · Jun 25, 2009

There is no mystery to the subnet mask, as many would have you believe. You can always take the simplistic view, so you don't get bogged down....

Simply convert your IP addresses and Subnet Mask to Binary notation, then :

a> where there is a "1" in the subnet mask, the "1"s and "0"s of the IP addresses must be the same. This is the Network Number, or NetID.

b> where there is a "0" in the subnet mask, the "1"s and "0"s of the IP addresses must be different. This is the Node or Host Number, or HostID.

MannyM · Jun 25, 2009

Node should be the lowest reference point.

daba · Jun 26, 2009

MannyM said:
Node should be the lowest reference point.

Please explain your meaning of that statement.

There is no requirement for a Node to be lowest, highest, sequential, or anything.

A node number can be anything it likes as defined by how many bits the subnet uses. However, there are two exceptions.

Take the SubNet Mask 255.255.255.0 for example.

In Binary this is :-

11111111.11111111.11111111.00000000

24 bits are used to define the NetID, and 8 bits are used to define nodes within that subnet.

That allows NodeID to be anything from 0 to 255.

00000000 = 0
11111111 = 255

However, node 0 will be the reserved gateway address for the subnet, and node 255 is reserved for multicast messages to all nodes within the subnet.

Your posted comment makes no sense to me.

surferb · Jun 26, 2009

Yes - under your "advanced" TCP/IP settings, you can bind a second IP address to your laptop's adapter. For example (192.168.1.254/24 and 192.168.0.254/24). The PLCs won't be able to talk to each other, but your laptop should be able to communicate with them all.

The responses above me address putting all the PLCs on the same network so that everyone can talk to each other. A router could also address that.

stu said:
i guys another question for you, i have quite a few allen bradley plc on our machine's and they all have different ip addresss what i am asking is can i set up moer then one ip address on the laptop so i can talk to the plc,
the laptop ip is = 192.168.1.254
1 machine ip is = 192.168.0.20
2 " " " " = 192.168.0 101
3 " " " = 192.168. 1 .50
4" " " " = 192. 168.1.80

CAN I TALK TO THE PLCS WITHOUT CHANGING THE IP ON THE LAPTOP ALL THE TIME.

The Plc Kid · Jun 27, 2009

How many different ip addresses can you bind to one network adapter?

Can the third Octet be the only thing that is different?

I am an ethernet noob and i thought i had a good understanding of the addressing but the above makes no sense to me?

I don't understand how it could work?

Why can the pc talk to both networks but the plc's not?

surferb · Jun 27, 2009

PLC Kid - take a look at this link. This situation assumes that everything is "wired together".

1. I don't know of a limit for how many addresses you can bind to an adapter. Most operating systems/hardware will let you bind many. Best practice is usually one.

2. You can use any legal IP address(es).

3. It's not all that much different to the Operating System than having 2 adapters with an IP address each.

4. Based on the address scheme (IP address and subnet mask), those nodes are on separate logical networks. Such PLCs will ignore traffic from each other. The PC has a legal address on both networks. Google "what is a subnet mask" for a better explaination.

The Plc Kid said:
How many different ip addresses can you bind to one network adapter?

Can the third Octet be the only thing that is different?

I am an ethernet noob and i thought i had a good understanding of the addressing but the above makes no sense to me?

I don't understand how it could work?

Why can the pc talk to both networks but the plc's not?

sthompson · Jun 27, 2009

The Plc Kid said:
How many different ip addresses can you bind to one network adapter?

Can the third Octet be the only thing that is different?

I am an ethernet noob and i thought i had a good understanding of the addressing but the above makes no sense to me?

I don't understand how it could work?

Why can the pc talk to both networks but the plc's not?

I am not sure what the maximum is, but I have a PC and Laptop with 3 IPs running on them.

The Mask is binary, and can be just about anything, there are lots of calculators and other resources on the Internet to figure this out.

With a Mask of 255.255.255.0 the interface can only talk to addresses on the same Class C Subnet. i.e. any address that starts with 192.168.1 but not with an address that starts with 192.168.2

Actually, if you change the Net Mask, it is might be possible for the PLCs to communicate with each other. I have never tried it. I have all my PLCs on the same subnet. It would be an interesting experiment.

gmferg · Jun 27, 2009

Changing mask on PLCs will allow them to talk to each other. I have done this at a customer's site with the following setup:

PLC1 IP: XX.XX.2.34 S/N: 255.255.254.0
PLC2 IP: XX.XX.3.50 S/N: 255.255.254.0

Laptop DHCP: IP: XX.XX.16.XX S/N: ???

I don't recall what the subnet was for my laptop. It is assigned by DHCP. I do recall that the 3rd octet of IP was 16.

Laptop is able to talk to both PLCs and PLC1 and PLC2 are messaging data back and forth.

surferb · Jun 28, 2009

It's not clear that OP wants everything to communicate together, or whether he can change the PLC addresses willy-nilly. You're absolutely right though, changing the subnet mask to 255.255.254 would allow all the nodes to communicate.

gmferg said:
Changing mask on PLCs will allow them to talk to each other. I have done this at a customer's site with the following setup:

MannyM · Jul 10, 2009

Daba, node being the lowest access address for any PLC network, from my understanding. Beyond that, you access the PLC datafiles via other means.

surferb · Jul 10, 2009

I'm not following what you're talking about. They were referring to "nodes" on a network as in "devices with an IP address", specifically, convention on what addresses to use. For example, the first is reserved for the network and the last for broadcast. Beyond that, it shouldn't matter (unless your organization consistently agrees otherwise).

MannyM said:
Daba, node being the lowest access address for any PLC network, from my understanding. Beyond that, you access the PLC datafiles via other means.

MannyM · Jul 14, 2009

Please define network and broadcast with respect to either bit assignment or eitherwise. Node from a design point of view, should remain the gate to open. Beyond that, it is quite another story.

Please rectify me if I am wrong on this subject.

jonnies · Jul 14, 2009

I have a purely theoretical question about this topic. It seems like subnet masks, in binary, are always split into 1's on the left and 0's on the right. What would happen if a subnet mask was something like 255.255.31.0, or 11111111.11111111.00001111.00000000? Would the network ID be the first two values, and the last half of the third value? Or is it only read until the first 0 is found?

rslinx and ip addressing

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