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In our continuing protocol tutorial series, we now turn our focus from SNMP to a broader yet critical element of network management - IP addressing.
Static assignment of IP addresses is typically used to eliminate the network traffic associated with DHCP/DNS and to lock an element in the address space to provide a consistent IP target.
An IP address is a unique number that points to an element identity on a local network.
Your cell phone has a unique number assigned to it so it can receive and send calls. Similarly, network elements have an identifying number called an Internet Protocol Address. In fact, that Smart Phone you use to surf the web has one assigned to it too. However, you'll most likely never see it unless you look for it.
The basic rule is simple: every network device is assigned a unique IP address. There are two types of IP addresses, static or dynamic. The difference between static and dynamic IP address assignment is that dynamic IP addresses are on an as-needed basis, while static IP addresses usually are on a permanent basis.
Let's look at the difference between static and dynamic addresses, and why it matters.
The differences between static and dynamic networks.
Let's start with a simple static IP tutorial. Static IP addresses are just that: Static, and they rarely change.
Just like your name, once a static IP address is assigned a network element, it remains there until a decision is made to change it.
At this time, the basic IP address structure is a 12 number address configured in this pattern: xxx.xxx.xxx.xxx. So, for example, a network element might have a static IP address like 209.134.004.168. Referencing that address on the network would always point to that network element, just like your phone number always refers to your phone.
The benefit of static IP address vs dynamic is the speed at which it can be referenced. Since the number never changes, and always refers to the same network element, it can be immediately accessed with no overhead processing.
Now, let's consider the dynamic IP address configuration. The opposite of static IP assignments is the Dynamic Host Configuration Protocol (DHCP).
The IP address of different devices connected to the network are automatically assigned to it as they come online by a server. This allows for IP addresses to be managed efficiently by providers with a large user base. Not all of the IP addresses will be allocated at one time.
A DHCP server allows a dynamic assignment of IP addresses in a system to those network elements that require them at a given time.
In order to be functional, a DHCP web server uses a system to track and lookup IP address information that relates to the active network elements.
One of the tools that allow this translation is the Domain Name System or DNS. The dynamic DNS server is like a card catalog in the library: it identifies the proper location of a network element and points network traffic to it when required.
This process of looking up IP addresses and routing traffic to them requires some overhead processing and time. In networks that do not require it, static IP assignments are often used.
Static assignment of an IP eliminates the network traffic associated with DHCP/DNS and locks an IP element into a specific address to provide a consistent IP target.
Telemetry monitoring masters can then be told precisely where the element is located by entering the IP address. You can observe this effect by replacing a typical WWW reference with its direct IP address if you know it. For example, enter "209.240.134.104" in your browser address bar and, with no DNS overhead, you will reach the same web page you would reach by entering www.dpstele.com.
When considering which IP addressing method to use for alarm monitoring, please know that using DHCP isn't the smartest solution.
You'll be wasting your time configuring your RTUs to report alarms to your master (i.e., T/Mon) with a specific IP address, knowing that it'll change.
The DHCP lease for your master's IP address will then expire within a week or so. As a result, your master will be given a new IP address. While all of this is happening, your RTUs will still be sending alarms to the specific IP address from your initial configuration. Because your master now has a new IP address, it will fail to receive the alarms.
You'll then have to waste more time configuring your RTUs to send alarms to this new IP address, knowing that it'll change again once the DHCP lease expires. This is equivalent to changing your phone number every week and notifying everybody in your contacts.
Instead, static IP addresses are used in telemetry monitoring. You'll only have to configure your RTUs once and know that your master station will receive the alarms.
Your preferred IP address will never change unless you decide to change it for some reason. Your master will be able to receive the alarms from your RTUs without failing due to a change in IP address as with DHCP. You'll avoid the hassle of configuring your RTUs all over again because your master's IP address won't change.
As a result, you'll have full control over your network with your IP locked down and remaining the same. Your static IP will make sure your alarms are received by your designated master.
Static addressing is crucial for remote access. If you have an RTU in the field and it is hours away, you do not want that RTU's address to change. If it did, you wouldn't be able to access the unit until you drove out to the site to figure out what it changed to.
In home networks or for workstations in large to small businesses, DHCP is typically used to automatically assign an IP to your devices. This is fine in most cases because these devices aren't being targeted or accessed regularly for anything. You don't care what the IP is, so it's okay if the IP address changes.
We've established static IPs as the preferred method for communication. But have you ever wondered how a remote site with no Ethernet can send alarms to a master station? What about sites with T1 or fiber connections, how are their alarms sent to their master station?
First and foremost, you'll need an RTU that can support T1 or fiber connectivity. Fortunately, there are RTUs with T1 or fiber interfaces that can provide LAN to the devices at your remote sites.
