Geekzone: technology news, blogs, forums
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.

2017 posts

Uber Geek


# 99982 31-Mar-2012 08:48
Send private message

Folks, my router is set to act as a DHCP server in the usual manner, viz. devices connecting to the network are assigned IP adressess from the stipulated range.

I connect another device where I have set a specific IP address, then naturally the router will assign that when the device comes 'online'.

My question is, what happens in the situation of where, for example, a couple of other devices are connected to the network first, and then the device with the pre-defined IP address is connected?

Presumably the first two devices are assigned IP adresses, say and .4, but then the device with the pre-defined IP address of say attempts to connect.

Does the DHCP server 'shuffle' the devices about, thus assigning the pre-defined device its correct IP address and then re-assigning the other two up the list?

I can see the value of assigning pre-defined devices somewhat high on the IP list, e.g. to overcome any conflicts, and even reserving that address in the router too.

Tks, R.

Create new topic
701 posts

Ultimate Geek

  # 602810 31-Mar-2012 08:56
Send private message

There's normally two ways to do this.

Method 1 (which I would recommend):
With your DHCP set a range that leaves some IP addresses free.  E.g. Set the range to -  Then with your device that you want to have a fixed IP address use one above that range.  E.g. (or higher).

Method 2
In your DHCP settings you can (depending on your router/software) set a reserved address for the MAC address of the device.  In this case you might choose as the address in the range that you want your device to have.  Your DHCP device will only allocate that IP address to the specified MAC address.  As it happens the device will never ask for it (unless you want it to get its IP address from DHCP but always get the same address) but DHCP wont allocate it either.

Method 1 is probably the easier and its what I do on my LAN as I'm always playing with VMs for various things and therefore always give them address outside of the DHCP range knowing its free (unless of course I've used it for a previous VM).a

Edit: To answer your question about "shuffling" the IP addresses in a conflict...
Sort of.  If you have a device that has a fixed address (I'll use the example again...but with no reservations set) its quite possible that a DHCP assigned device will get the .10 address.  When you then connect your fixed IP device, which also has a .10 address, a IP conflict will be detected.  I'm not too clear what would happen here.  The second device coming on line (so the fixed one) might spot that .10 is in use and therefore not connect.  Or it might bulldoze its way in and the DHCP assigned one spots the conflict so requests a new address.

Use one of the methods above to avoid this :)

2017 posts

Uber Geek


  # 602813 31-Mar-2012 09:09
Send private message

nzkc, thanks for that and yes, I figured methods 1 or 2 would resolve any conflicts.

Howvere, I was just wondering what would happen in the non-specified scenario ... maybe I just have to set up a test and try it out?



1716 posts

Uber Geek

Lifetime subscriber

  # 602824 31-Mar-2012 09:59
Send private message

you can also assign specific ip addresses to a particular MAC address, each device has it's own unique MAC address, so the router will only assign that paericular ip adress to 1 device

2017 posts

Uber Geek


  # 602834 31-Mar-2012 10:21
Send private message

Greg, yup, all known, thanks.

It's the non-specified situation I was wondering about.


701 posts

Ultimate Geek

  # 602955 31-Mar-2012 16:38
Send private message

Conflicts are detected, how they're handled may depend on the OSes involved.

22524 posts

Uber Geek


  # 603084 31-Mar-2012 23:18
Send private message

I know that the windows 2003 DHCP server would go thru and make reservations in the range if things conflicted _sometimes_ so that address didnt get dished out, other time it would happily assign an address that I had already put into a printer or something else on the lan making everything really really flakey unless the PC happened to tell me about a confliting IP address, which was not very often.


Create new topic

Twitter and LinkedIn »

Follow us to receive Twitter updates when new discussions are posted in our forums:

Follow us to receive Twitter updates when news items and blogs are posted in our frontpage:

Follow us to receive Twitter updates when tech item prices are listed in our price comparison site:

News »

Microsoft New Zealand Partner Awards results
Posted 18-Oct-2019 10:18

Logitech introduces new Made for Google keyboard and mouse devices
Posted 16-Oct-2019 13:36

MATTR launches to accelerate decentralised identity
Posted 16-Oct-2019 10:28

Vodafone X-Squad powers up for customers
Posted 16-Oct-2019 08:15

D Link ANZ launches EXO Smart Mesh Wi Fi Routers with McAfee protection
Posted 15-Oct-2019 11:31

Major Japanese retailer partners with smart New Zealand technology IMAGR
Posted 14-Oct-2019 10:29

Ola pioneers one-time passcode feature to fight rideshare fraud
Posted 14-Oct-2019 10:24

Spark Sport new home of NZC matches from 2020
Posted 10-Oct-2019 09:59

Meet Nola, Noel Leeming's new digital employee
Posted 4-Oct-2019 08:07

Registrations for Sprout Accelerator open for 2020 season
Posted 4-Oct-2019 08:02

Teletrac Navman welcomes AI tech leader Jens Meggers as new President
Posted 4-Oct-2019 07:41

Vodafone makes voice of 4G (VoLTE) official
Posted 4-Oct-2019 07:36

2degrees Reaches Milestone of 100,000 Broadband Customers
Posted 1-Oct-2019 09:17

Nokia 1 Plus available in New Zealand from 2nd October
Posted 30-Sep-2019 17:46

Ola integrates Apple Pay as payment method in New Zealand
Posted 25-Sep-2019 09:51

Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.

Support Geekzone »

Our community of supporters help make Geekzone possible. Click the button below to join them.

Support Geezone on PressPatron

Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.

Alternatively, you can receive a daily email with Geekzone updates.