IP addresses and wi-fi

[RogerS]

Can anyone please shed any light on something that I don't understand regarding IP addresses and wi-fi.

I have a wifi access point in my study. It's IP address is 192.168.0.13 and is there in my Router Attached Devices table.

I have an iPod touch that is connected to the network via this wifi access point. If I go into my iPod Touch to look at the IP address, it tells me that it is 192.168.0.12. However if I look at the router attached devices table I do not see this IP address. Neither do I see it on the Mac after running Fing from the Terminal.

1) So how does the iPod Touch 'work' with the network?

2) And what would happen if there was a second device connected via the wifi access point?

3) What is there preventing the router assigning 192.168.0.12 to another device at the same time as the iPod Touch?

4) What assigned the IP address of 192.168.0.12 to the iPod Touch?

V confused.

TIA

 

[Myfordman]

I would presume that your AP is allocating wifi IP addresses to wifi devices.

If you look at the set up software for your AP it will possibly allow you to set the range of IP addresses that it can assign.

It is a bit like the NAT Network Address Translation that your router does to allow every device on your network to appear to have the same IP address when viewed from the outside world.

 

[dm65]

If your router is something like the ones that bt supply, you may see it as an unknown device

I would expect, as myfordman said, that your router is running dhcp and therefore if you can find an allocation table on the router rather than a list of devices, you should see the ip listed (and again, its mac address)

You shouldn't need to worry about duplicate or conflicting ip addresses as the router will know whats in use so you should be able to add many more devices without causing a problem as long as all these use dynamic ip addressing

If you manually configure one of these devices, you need to know what the dhcp range is - ie what addresses will it give out - you may see either a number of addresses to use plus a starting address, or you may see a range of ip's - 192.168.0.10 - 192.168.0.100 for example

Network scanners may well 'see' the ip and show its mac address but no more than that

What router are you using ?

 

[RogerS]

Netgear DG834G

Just checked and 0.12 is now there. So maybe the router was a bit late in updating its tables when I looked at it the first time?

So all seems OK now and makes sense that the router is assigning the IP address 'through' the AP.

Many thanks for the input, guys.

 

[mseries]

I have just installed a DG834G and have noticed that the Android devices seem to come and go, I was a little surprised but it's OK. I suspect that the connection isn't 'permanent' and re-established when needed. Or maybe this part of the DG834G is flaky !!! (I don't think I observed this on my Thomson TG585 but this has other problems which is why I have replaced it)

It's usually the job of the DHCP server which is usually a component of the router to assign IP addresses to attached devices whether they are wireless ones or not and the DHCP server does not give the same address out to more than one device at the same time.

it is possible to set devices up with a static IP, I have one server on my LAN which is 192.168.0.2 and it does not get this from the DHCP. The DHCP is programmed to assign addresses in the range 192.168.0.50 to 192.168.0.254 and for some I have instructed the DHCP to always use the same address but remember the DHCP assigned the address in the first place. Have a know IP whether static or fixed in the DHCP is useful if you need to contact the device directly by it's IP address (which I do since I don't have a DNS to map their names to their addresses).

I hope this helps and is not too confusing. Please feel free to ask more, I am not a networking expert but do work with computers and know a bit about it.

 

[RogerS]

Yes I also have some static IP addresses set-up. I have an HP laser printer that has a very strange beast to act as the interface to Ethernet and it is a bugger to set-up if I ever need to do it....that one has a static IP address. Plus I had an address conflict with two devices...shouldn't happen, I know, but it did. So one of those has a static address.

One niggle with that Netgear router is that you can't give names to attached items as far as I can see. Too many "Unknown" but as the same devices seem to end up with an ongoing IP address I've got to 'know' them.

 

[mseries]

yes, if you just use dynamic IP with no reserving, it doesn't remember any device names, If you reserve an IP for a device you can give it a name and it will remember it. In my view below Gimondi and Kelly have reserved IPs , the UNKNOWN does not

The attached devices isn't reliable is it.I just looked at mine and the computer I am using was't showing, press refresh and it does !!!

Another interesting point about this router, interesting meaning I don't fully understand, is that the router seems to be honouring some sort of request from the device for a specific IP. In the image above 192.168.0.68 is my Nexus 7 and 68 is the IP that my previous router assigned to it (I replaced the previous router with the DG834G about 10 days ago). One would think that the DG834G would choose the next available IP which will be 59 or 60. It looks like the Nexus has said "can't you give me 68" and the DG834G has done so. I have seen another example of this where my laptop has connected wirelessly and wired at different times and been allocated the same IP address, like the IP stack has requested/suggested an address rather than the MAC address.

 

[monkeybiter]

Where do 'lease times' figure in this? If a device is reconnected within the preset lease time won't it retain the same IP assignment?

Re. the device names, even using DHCP they are usually reported as the device name assigned by the user or preset in the device as opposed to a name you might assign in the router.

 

[mseries]

monkeybiter, that's my understanding of lease times too. The DG834G doesn't let the user change the lease time value and does say what it is as far as I can tell.

Device names: yes again, but the DG834G isn't showing everything, whether the devices are sending the information or not I can't be sure. I think my Linux ones are but the Androids don't have names as such and they are showing as UNKNOWN. I do remember my Thomson router worked better in this respect, too well though as it remembered all sorts of test machines that once were on the network. The Thomson TG585 did not pass SSDP packets reliably though so had to go.

 

[Eric The Viking]

Roger,

Any web interface won't/can't be real time. You have to refresh the page to see a change. The page can have an auto-refresh in the header, but that's not guaranteed to be correct. Ctrl+F5 in the browser will help, but again isn't always correct.

I've got three Edimax WiFi APs that I'm just about to ditch as they're so awkward to set up and won't play nicely together: I'd like them to do DHCP for wireless devices, but I can't stop them trying to do DHCP for the rest of the network. If I turn DHCP off, the wireless connections are very slow. One of the issues is that they've written the interface to look like it's real-time, when it isn't. You can waste a lot of time on that...

The definitive test of connectivity is to ping the device, by its IP address, from a terminal, either Windows command line or a Linux/Mac/Android terminal window. If you get a reply from 192.168.0.12 then you know it's there, no matter what the web interface says. Fing will let you do this, but it too gets a bit confused sometimes (I run it on my Android tablet).

Is your HP laser using a JetDirect card? If so, there is, or was, a good free management tool on the HP web site: "HP Web JetAdmin". It's overkill for one printer, but still useful. Both my HP printers have JetDirect cards (EIO ports) and they're pretty much bomb proof.

Cheers,

E.

 

[RogerS]

.....a good free management tool on the HP web site: "HP Web JetAdmin". ....

E.

LOL...been there..done that...the version I got wanted me to load a whole slew of stuff because JetAdmin is designed for enterprise wide networks of printers.....!!