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Subnet Mask changes from 255.255.255.0 to 255.255.0.0 causing VPN connection to drop

I have a problem occurring on my wireless at home where after being connected for a while my subnet mask gets corrupted. It goes from 255.255.255.0 to 255.255.0.0. When this happens, my VPN drops and the network no longer functions on my laptop. The only way I have found to correct this is to power cycle my wireless router. Trying to renew or repair the IP from my laptop does not work. This does not happen to my desktop that is tethered to the same router....Any ideas on what to look at to fix this?

I almost always use the my laptop to do work from home via a VPN. The router is a US Robotics 8054 and I use DSL.

Any ideas would be really appreciated, Thanks!



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willmrk
Asked:
willmrk
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2 Solutions
 
zephyr_hex (Megan)DeveloperCommented:
do you have the latest firmware on your wireless router?  if not, do a firmware upgrade.
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willmrkAuthor Commented:
Yep. Latest firmware (sorry, forgot to mention that).
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bstrauss3Commented:
What is the ip address before and after the change?
How long are you on-line?

-----Burton
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HenrikrpCommented:
It looks like a DHCP Problem. When it happens, what IP do you have when typing IPconfig /all ? try it before and after the problem occurs
If it starts with 169.254.x.x try a static IP on your laptop.


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willmrkAuthor Commented:
Burton and Henrikrp,

Thanks for your questions and comments. Once it happens again I will post your answers.

thanks again for your support!!
willmrk
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Craig_200XCommented:
I agree with the other two.. looks like a router prob.. do you have other computers this happens too also? have you tried another router?
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advsoftCommented:
In order to properly troubleshoot, need to know:

IP address and subnet mask on wired machine (before and after problem)
IP address and subnet mask on wireless machine (before and after problem)
Router IP and subnet mask (before and after problem)

Thanks.
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willmrkAuthor Commented:

IP address and subnet mask on wired machine (before and after problem) : wired machine not in use and not powered on
IP address and subnet mask on wireless machine (before and after problem) : Subnet: 255.255.255.0 IP 192.168.123.100 After: subnet 255.255.0.0 IP 169.254.143.100
Router IP and subnet mask (before and after problem) : Cannot access router to check IP without resetting.

Note I was connected for 20 min prior to issue. Also when I do a IPCONFIG, there is a default gateway set to 192.168.123.254 when the issue occurred this went to 0.0.0.0

Thanks!
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bstrauss3Commented:
169.254.x.x is a special range to allow peer-to-peer networks (i.e. without a router).  Basically each device picks one address in that range, makes sure nobody else is using it and goes on it's merry way.

So what appears to be happening is that you are getting a very short lived DHCP address (192.168.x.x), probably from the Cable/DSL Modem.  After the network is established, when your machine tries to renew the address, there's now no DHCP server, so it times out and shifts to the 169.254 address.

Something is wrong with your gateway/router.    This can happen if your gateway/router starts up running in bridge mode - the initial request gets bridged to the CM.

One nasty trick with the 169.254 addresses is that they don't support release/renew.

(1) Make sure that the Cable/DSL Modem is up BEFORE your gateway/router.
(2) Wait until the lights settle down, then boot the gateway/router.
(3) Finally boot the computer.

This will get it's initial address from the gateway/router and all should be ok.

-----Burton
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HenrikrpCommented:
Try a static IP on your laptop. That should solve it.
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