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60wag
10-20-2010, 08:11 AM
Our in house IT department should be able to answer my question but thinking outside the box isn't one of their strong suits.

Anyhow, I've several pieces of equipment that use ethernet to communicate among devices on the equipment. Within a machine I have an array of addresess like 192.168.21.5, 192.168.21.6, 192.168.21.7, etc. On another machine the addresses are 192.168.35.1, 192.168.35.2, etc. The addresses among different machines were not coordinated. Now I want to connect the machines to a common network to collect data from them. My basic understanding of IP protocol says that the first three numbers in the address have to be the same to be able to pass information to a common device - like a PC. Changing the addresses on the machines to be similar is a major PITA do to validation requirements.

Can I plug the machines into a router, or something similar, that can take the disimilar addresses and alias them into something that my data collection system can use? If I can, what is this method called? I found something called Network Address Translation that looks promising but I not sure. Whatdya think?

leiniesred
10-20-2010, 08:37 AM
Bruce: It might be easier to open up the subnet mask to include both networks.
255.255.192.0 is the tightest mask you can use and include the two networks on the same segment. That will cover 192.168.0.0 to 192.168.63.255. (about 16,000 addresses)

The "first 3" octets is only important if your subnet mask happens to be 255.255.255.0 (sometimes called a "slash twenty-four" because that is a 24 bit subnet mask.)
If you change the subnet mask to 255.0.0.0, now only the first octet is important.
Subnetting can get confusing fast, Here is a great tool to help you understand how subnetting works because you can see instant results of the different masks:
http://www.solarwinds.com/products/freetools/free_subnet_calculator.aspx


NAT will also work. Any decent router should be able to NAT those addresses for you.
link to example of cisco dymanic NAT configuration. (the translations are generated on the fly based upon a certain set of rules considering the source IP, the destination IP and any other requirements you put in there.)
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a0080093f8e.shtml

If the number of network devices in the .35 network is small and static, you could also build static NAT rules on the router to handle the translations. The advantage of using a router is that you don't have to go and touch every network device that you want to get to talk to the 21 network.

coax
10-20-2010, 08:42 AM
Our in house IT department should be able to answer my question but thinking outside the box isn't one of their strong suits.

Anyhow, I've several pieces of equipment that use ethernet to communicate among devices on the equipment. Within a machine I have an array of addresess like 192.168.21.5, 192.168.21.6, 192.168.21.7, etc. On another machine the addresses are 192.168.35.1, 192.168.35.2, etc. The addresses among different machines were not coordinated. Now I want to connect the machines to a common network to collect data from them. My basic understanding of IP protocol says that the first three numbers in the address have to be the same to be able to pass information to a common device - like a PC. Changing the addresses on the machines to be similar is a major PITA do to validation requirements.

Can I plug the machines into a router, or something similar, that can take the disimilar addresses and alias them into something that my data collection system can use? If I can, what is this method called? I found something called Network Address Translation that looks promising but I not sure. Whatdya think?

I'll throw in my two cents but its been a while since I've done any real networking.

First, a few basics from what I remember. There are 3 IP ranges that are reserved for "internal routing" meaning you can't access them from the internet at large. 10.x.x.x, 172.16.x.x, and 192.168.x.x. So if I understand your issue, you have multiple overlapping class C subnets that need to talk to each other.

NAT is most commonly used for putting an internal subnet like the above behind an externally routable IP address on the internet. For example, I get one IP from my broadband provider, but I have 5 computers or devices behind that, all with 192.168.1.x internal IP addresses. NAT gets fairly complicated, but it uses ports on the external IP address to map to different ports on a unique internal IP address.

I assume that you are using fixed IP addresses for each device and not DHCP? Now physically, how are your devices set up? Like could you get cable between them? Or what device is assigning the IP addresses now, if any?

If each "group" of devices is on some sort of switch, there is a chance that you could use the uplink on each of those switches into a new switch? What this may do is have a unique address for each of these routers, and NAT *may* then be able to work across multiple switches. In short doing any sort of manual setup for NAT would require (imo) more work than potentially re-ip'ing your devices. But that would depend on how many ports these devices use, etc.

" My basic understanding of IP protocol says that the first three numbers in the address have to be the same to be able to pass information to a common device - like a PC."

I don't believe this is the case. It all goes back to the internal vs. external address space. But if they are all on the same network it makes things quicker/easier.

"Can I plug the machines into a router, or something similar, that can take the disimilar addresses and alias them into something that my data collection system can use?"

Maybe...but as far as I am aware, there is no "aliasing" that can be done at the IP level. NAT is probably as close as you will get but again, that use a combination of ports and ip addresses to make unique identifiers.

Anyway, hope this helps. Just what I recall from a while back so it may not be 100% correct. Good luck w/ the project! Happy to try and help if I can. :cheers: