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Author Topic: Router using different subnet masks  (Read 2038 times)

Router using different subnet masks
on: September 09, 2006, 11:00:21 AM
Further to the problems i was having before it seems that my speedtouch router is assigning IPs with different subnet masks to different devices (at random). The two IP ranges it uses seem to be:

192.168.1.x (which is the one it uses for itself)
and 84.9.13x.xxx

I cant see any settings to correct this, short of using static IPs for all the devices.

The IPs are not specific to any particular device, it changes when I reset the router.

Any ideas?
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Formerly sexytw
Re:Router using different subnet masks
Reply #1 on: September 09, 2006, 12:01:52 PM
Surely the second range is for the WAN side, not assigned by the router but to it by the ISP...
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Re:Router using different subnet masks
Reply #2 on: September 09, 2006, 12:16:28 PM
Yup as 84 isnt a local addy.
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  • Offline Mardoni

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Router using different subnet masks
Reply #3 on: September 09, 2006, 12:44:01 PM
That is true but if the ISP are allowing him a number of public IPs the router maybe intelligent enough to dish those out before falling back onto private IPs.

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Router using different subnet masks
Reply #4 on: September 09, 2006, 16:31:03 PM
how do i stop it using the public IPs? It seems I get 2 public IPs then it allocates local IPs to the rest of the devices.

Thing is the ones on public ips cant see the ones on private ips and vicaversa. Its most annoying.
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Formerly sexytw
Router using different subnet masks
Reply #5 on: September 09, 2006, 23:39:54 PM
Quote from: sexytw
how do i stop it using the public IPs? It seems I get 2 public IPs then it allocates local IPs to the rest of the devices.

Thing is the ones on public ips cant see the ones on private ips and vicaversa. Its most annoying.



Does internet access work from both public and private IPs? If so its more than likley that you are being issued public IPs by your ISP. Which  router is it?
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Re:Router using different subnet masks
Reply #6 on: September 10, 2006, 10:23:36 AM
Yep, internet works on both.

Its a speedtouch 580i (forgot to mention that!).

This is an annoying problem, there doesnt seem to be any way of changing the subnet allocation in the router settings.
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Formerly sexytw
Router using different subnet masks
Reply #7 on: September 10, 2006, 12:04:51 PM
If the internet is working from the machines being issued public IPs its more than likley the ISP are issuing them...but as a final test go to www.whatismyip.com from a machine with a public and private IP and check that they are indeed different and that the machine being issued a public IP isnt being translated anyway.
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Router using different subnet masks
Reply #8 on: September 10, 2006, 19:18:57 PM
Computer with IP: 192.168.1.64
shows on whatsmyip as:  84.9.139.**

havent been able to check a public IP yet.
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Formerly sexytw
Router using different subnet masks
Reply #9 on: September 11, 2006, 17:47:22 PM
Computer with IP: 84.9.137.***
shows on whatsmyip as:  84.9.137.***

ie the same. What does this mean? Anything I can do?

This is the part in my router setup that seems to regulate it but it all looks ok:

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Formerly sexytw

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Re:Router using different subnet masks
Reply #10 on: September 11, 2006, 22:54:55 PM
Read the manual, try setting the ips manually and telling it to let the items keep them forever.

http://www.speedtouch.co.uk/downloads/580/E-DOC-CTC-20040123-0001_v3.0_public.pdf#search=speedtouch%20580i%20manual

If you still cant work it out ask at http://www.speedtouch.com they will know a lot more about their products than we do ;)
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  • Offline Mardoni

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Router using different subnet masks
Reply #11 on: September 11, 2006, 23:27:30 PM
Can you post up your public subnet mask ? That should allow us to figure out how many IPs the ISP is letting you have.

Have a look through your routers config and see if there is a place to specify static routes. The router may not (for some reason) be creating a route for 84.9.137. to your 192.168.1.. It should be possible to fix this, as long as your router allows you to add routes.

If not, you need to find out why your ISP is issuing you with additional IPs (they normally charge extra for this) and either get them to stop OR as serious has suggested force the LAN IPs on.

You should be able to force all of your LAN devices to 192.168.1.x addresses by doing the following:

1) Disconnect ADSL
2) Flush IP Assigment / Reset Router
3) Configure the correct LAN IP address range.
3) Boot up each device on your LAN, it should only receive a 192.168.1.x address as the DSL link is down.
5) Go through the router config and force each devices IP lease to perminate.
6) Plug the DSL back in.

The other alternative is to buy a different router, one that only supports a single public IP interface :)
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