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Connecting Stuff- Pt. 2

LAN static IP addresses/ DHCP servers

Material on this page © TK Boyd July 2017... but if you want to translate the page, or circulate it on DVD or intranet, I will allow that with some conditions.

This is one page of many in a sequenced series that try to get you connecting things to LANs and the internet with as few tears of frustration as possible. There is an overview page, which is your table of contents to this material.

This page, and the pages in my "Connecting Stuff" series has not yet had extensive editing. I apologize for the crudeness at this stage, but, unless you need "bells and whistles", and "slickness", I think you can find useful information here.

So far, I hope you've found the material here rather dull. I had to "set the scene".

Now we come to some things that may be new and strange to some readers. Some will lose interest. Others' eyes will glaze. Do you have The Right Stuff to Get There?

Remember that each machine on a LAN has a LAN address? I'm going to call that it's LIPA from now on. "Local Internet Protocol Address". It will PROBABLY be something like with the last number being something different for each machine on the LAN, and being something from, probably, 2 to 255. I don't think you'll ever see a machine at (I'm not sure why not, but it seems to be "a rule"! (Probably reserved for some special service.))

Usually, your switch/ router/ modem will have a LIPA of

The first three numbers may be different from the above in the case of your LAN, but all the devices on the LAN will (generally) have the same first three numbers as one another. Look particularly closely at the third number. It is not too unusual for that to be a 1. (If it is, it will need changing to "0" (usually) if you want it to "play nicely" on a LAN where everyone else is using 192.168.0.xxx. (Or vice versa... change one "oddball" 192.168.0.xxx to 192.168.1.xxx if most things... in particular the switch/ router/ modem are on LIPAs starting 192.168.1)

You can do LOTS without ever having to worry about what the LIPAs are in your world.

Now you are going to learn about why you haven't had to think about them before, and learn about Taking Charge. And with that power will come the ability to do new things.... including messing up how things work for your toys.

Simple, User Friendly LANs have a DHCP server. If you haven't worried about LIPAs before, your DHCP server is probably in your router. (It could be somewhere else, but that's unlikely.) Be careful: On a given LAN, there can be only one DHCP server. Don't get two going!

When a device connects to a LAN, it needs a LIPA. It can either bring a "static LIPA" to the party, or ask the DHCP server to ASSIGN it a LIPA. (In the latter case, the LIPA may well be different from one session to the next.)


a) a device sends a "please give me a LIPA" to the DHCP it hopes is there on the LAN it is connecting to, or...
b) It doesn't... in which case, when it was set up so that it doesn not ask for a LIPA, it was also told what LIPA to try to use...

....is a setting you (or someone!) made in the to-be-connected device BEFORE it even tried to connect to a LAN.

(You can change those settings WHILE something is connected to a LAN, but as soon as you do, it will probably lose its connection, and need re-connecting, which may entail a re-boot of the device. You probably won't to reset the LAN.)

There are, of course, pros and cons to both solutions. The biggest "con" of using static LIPAs is that YOU have to be sure that there are never two devices with the same LIPA connected to a particular LAN at the same time.

Most routers give you a way to see what devices... by LIPA... are connected, you'll be glad to know. The bad news? Some devices, while PHYSICALLY connected (or set up to connect via WiFi) only connect intermittently. They can be a real pain!

If you have ANY devices which will connect to the LAN via a static LIPA, you have to tell the DHCP server NOT to use the address that device uses when the DHCP "hands out" LIPAs. (And if you make a change to that setting, you need to do a major "round" of re-starting things. Turn connected devices off. Then power cycle the switch/ router/ modem. Then turn the devices on the LAN back on.)

You should almost certainly leave a DHCP server active on the LAN... but you will need to tell it, "Only give out LIPAs in the range 192.168.0.xxx to 192.168.0.yyy" (Those are typical numbers... and for xxx and yyy, I would be inclined to use 2-19. (You may want to specify a different "pool" of LIPAs for DHCP use, depending on your circumstances.)

Having set your DHCP server up, you will now know what LIPAs are "outside" the LIPAs used by the DHCP server... And THOSE are the LIPAs available for assigning as static LIPAs, for devices you want to connect via static LIPA.

Clear? As mud, perhaps... but re-read the above. You Can Do It!!

All this talk about static IP addresses may have caused you concern. You may have heard that "having a static IP address on the internet" is an expensive business.

Fear not! The static IP addresses we have been talking about here are the LIPAs of devices on the LAN side of your router. The expensive "static IP address" is a static IP address on the WAN ("internet"/ "outside") side of your router/ modem/ switch) YOU DON'T NEED a static IP address FOR THAT!



Why does all this stuff arise? Fear not... that will, I hope, become clear in the next part of this series.

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