Fixed IP Or DHCP

[astral]

I have been using a fixed IP on my home network 192.168.1.1 for my laptop for some time.

Last night my internet connection ground to a halt.

After trying the obvious tricks like power off the PC and modem I called my ISP.

They walked me through letting DHCP choose the address.........

Lo and behold the internet started working.

Now this does not make any sense to me.

Can anyone explain why??

PS I use fixed IP addresses to simplify access to my Dreambox on the network.

Don't ask which ISP, as I am not in Thailand.

Thanks

[siamect]

One thing that can happen it that someone else have got the same IP.

If you use fixed ip you need to reserve that ip in the DHCP server (usually in the router if it is a home network)

If you have a wifi network that is not encrypted then this scenario is really possible. If that is the case you should enable WPA2 in the router...

Martin

[garyh]

If you need a set ip address on the pc use one other than one ending in 1 like 192.168.1.5 this will still work with DHCP turned on as long the first 4 sets of numbers are the same ie the 192.168,1 part the last one can be anything up to 255

[trogers]

If you need a set ip address on the pc use one other than one ending in 1 like 192.168.1.5 this will still work with DHCP turned on as long the first 4 sets of numbers are the same ie the 192.168,1 part the last one can be anything up to 255

the last one can be anything up to 255...except 1, as the gateway of the LAN is usually 192.168.1.1

[Crushdepth]

Another possibility is that your DNS server died. Try using OpenDNS. Using fixed IPs is a good idea IMHO, keeps things simple and reliable.

[siamect]

...192.168.1.5 this will still work with DHCP turned on...

This is exactly the problem... this setup will be unreliable unless the fixed ip, in this case 192.268.1.5 is guaranteed to not already be occupied.

If the DHCP server has already give this IP to some other computer then you will have a problem and this problem will most likely come up after some time, even if it works from the beginning.

You should reserve this IP in the DCHP server so that the DHCP server never give this IP to anybody else....

Alternatively you can setup the DHCP server so that it always give the same IP to the hosts that needs static IP. That is the best solution, you never need to touch the settings in the computer.

Generally you should avoid static IPs at least on Laptops... you will have to mess with the settings when you need to access a public Wifi spot or when you visit friends and family...

Martin

[astral]

Thanks for the comments.

DNS should not be a problem with the 192.168.xxx.xxx address range.

It is all inside my home network with a totally different address to the ISP

No conflicts as the wireless door is firmly shut.

I now put it down to the ISP as I am back on the fixed IP address and it works again,

as it has done for several weeks in the past.

Call centre monkeys with their manuals

If I am on a public network is usually wireless, and that is set to use DHCP.

[garyh]

If you need a set ip address on the pc use one other than one ending in 1 like 192.168.1.5 this will still work with DHCP turned on as long the first 4 sets of numbers are the same ie the 192.168,1 part the last one can be anything up to 255

the last one can be anything up to 255...except 1, as the gateway of the LAN is usually 192.168.1.1

[endure]

If you need a set ip address on the pc use one other than one ending in 1 like 192.168.1.5 this will still work with DHCP turned on as long the first 4 sets of numbers are the same ie the 192.168,1 part the last one can be anything up to 255

On a Class C network (one whose subnet mask is 255.255.255.0 - as most home networks are) you can't use x.x.x.255 as it's the broadcast address.

[Eureka]

Thanks for the comments.

DNS should not be a problem with the 192.168.xxx.xxx address range.

It is all inside my home network with a totally different address to the ISP

No conflicts as the wireless door is firmly shut.

I now put it down to the ISP as I am back on the fixed IP address and it works again,

as it has done for several weeks in the past.

Call centre monkeys with their manuals

If I am on a public network is usually wireless, and that is set to use DHCP.

You have 2 devices mentioned attached to your Home Network. If the other device restarts when your computer is off, or if the router finds it before your computer then the Automatic IP addresses get reasigned.

Easy fix is to trun everything off then power up the modem.

Next turn on the computer and wait until everything has finished loading.

Next power up other devices.

[monty]

I usually try to use fixed IP addresses in my networks, but I have to admit my networks are bigger the usual, with a lot of different devices (network printers, dreambox, POS stations etc).

I always use a certain range for DHCP (can set this in your router), e.g. from 192.168.1.5 till 192.168.1.50 and then assign fixed IP's in a higher range.

My main reason is trouble shooting! If for some reason I can't see or reach a device, a quick ping will tell me the device is there or not, or that maybe the software I'm trying to reach is the culprit.

Also, I access all devices through their IP addresses, not through their computer/device names. The latter can sometimes muck up in windows as well, but never when using IP addresses!

[Supernova]

...192.168.1.5 this will still work with DHCP turned on...

This is exactly the problem... this setup will be unreliable unless the fixed ip, in this case 192.268.1.5 is guaranteed to not already be occupied.

If the DHCP server has already give this IP to some other computer then you will have a problem and this problem will most likely come up after some time, even if it works from the beginning.

You should reserve this IP in the DCHP server so that the DHCP server never give this IP to anybody else....

Alternatively you can setup the DHCP server so that it always give the same IP to the hosts that needs static IP. That is the best solution, you never need to touch the settings in the computer.

Generally you should avoid static IPs at least on Laptops... you will have to mess with the settings when you need to access a public Wifi spot or when you visit friends and family...

Martin

It's best to assign client machines fixed IPs using addresses outside the DHCP pool. Reserving IPs isn't necessary, unless you intend to use IPs from the DHCP pool. Most routers allow you to configure a range (Start IP - End IP) to be used by the DHCP server. Fixed addresses don't have to be within this range.

For example -

In this scenario, PCs native to the network can be given fixed IPs in the sub 100 range (2 - 99). PCs outside the network, when connected are automatically assigned 101, 102, and so on by the DHCP server. As you can see, there's no potential for IP address conflict. I run a similar setup on my home network.

[siamect]

It's best to assign client machines fixed IPs using addresses outside the DHCP pool. Reserving IPs isn't necessary, unless you intend to use IPs from the DHCP pool. Most routers allow you to configure a range (Start IP - End IP) to be used by the DHCP server. Fixed addresses don't have to be within this range.

I fully agree with you when it comes to home and smaller network. Maybe silly of me to suggest reserving in this case...

However when you set up a DHCP server that serves multiple subnets I still prefer to use a range for each subnet and then reserve or force those hosts that need static IP...

Martin

[astral]

The Dreambox has .99 as its address, outside of the DHCP range

and my lap top is the only other device on the network.

Unless friends are visiting, and they are not at present.

The fixed IP for the laptop is recommended by uTorrent,

but to be honest I cannot see that it makes any difference

to performance.

[siamect]

The Dreambox has .99 as its address, outside of the DHCP range

and my lap top is the only other device on the network.

Unless friends are visiting, and they are not at present.

The fixed IP for the laptop is recommended by uTorrent,

but to be honest I cannot see that it makes any difference

to performance.

Performance should be the same.... you use fixed IP so that you can setup the router to route incoming traffic.... In this case to your Dreambox if you need to access it from outside.

Martin

[Llareggub]

I'll keep my mouth shut, sorry, i didn't realise you were referring to a Dreambox, whatever one of those is!

[trogers]

I tried to enable a static address for my PC, shared with my son on two computers, all I wanted to do was to ensure that I retained 192.168.0.2 and he kept 192.168.0.3, but as yet I have never been able to do it, it seems to depend on who logs on first as to who gets the 2, or the 3, if I try to fix the address, ( lock the router to my pc with the DNS as 192.168.0.2) I end up unable to connect.

If you want to fix static LAN addresses for your home computers, use the range of IP addresses that the router's DHCP will not dish out.

Fix your computer with 192.168.0.12 and the other with 192.168.0.22

Any new computer, say a laptop of a visiting friend, would probably be issued 192.168.0.2 by the DHCP.

http://portforward.com/networking/staticip.htm