Turn 2nd PC on, lose connectivity on both.  Cable Modem / Router issue.

Posted on 2003-10-26
Last Modified: 2013-12-14
I reassigned IP addresses using an SMC Barricade router.  Its set up as a DHCP server and consistently assigns IP addresses to two computers.  The router is now taking in a WAN connection directly from a cable modem, instead of from another router of exactly the same make/brand.

Its still running off a cable modem as before, but as a separate network now.

The behaviour is consistent.  If I turn off the cable modem, then router, then turn on the cable modem, then the router, then boot my first PC, it can access the internet (like I'm doing now).  But turn on the 2nd PC and whoops... neither can get past pinging the router address.  

IPs are as follows:


DNS, DHCP and Default Gateway all

DNS, DHCP and Default Gateway all

Used to be in the, 100-106 range before this change.

The DHCP leases from the router look OK, and are good for a week.

Why, when I turn PC2 on does PC1 lose its connection, and PC2 never can connect to the internet?

Question by:RadRichie
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Expert Comment

ID: 9636059
Turn on PC2, leaving PC1 powered off, to see if PC2 works ?

Check that your subnet masks for all devices are the same ( in this case. Just to be sure. Make sure that both PCs are obtaining their IP address from the router/DHCP server. Make sure you did not configure any alternate IP address on either PC. This setting's under TCPIP properties, Alternate Configuration.

Let us know how it goes.

Expert Comment

ID: 9664203
Guess that it could be a NAT problem in the router:

Try switching router on/off (leave the rest running), - turn on router and see if PC1 can browse

If ok, see if PC2 can browse (probably not)

Power router on off again, start with PC2 this time

same problem ?

If yes, try:
  set all your IP's < (note the complete subnet address!)
  set your router config accordingly

This is not a satisfying solution (if it works...)  I know, but I had a similar problem once, which I solved in that fashion, bud didn't have time to investigate further, so I can't explain the cause ;-)

Author Comment

ID: 9664422
- PC2 works for a bit sometimes when PC1 is turned off.  Then its internet connection dies, but its IP and DHCP lease information remain.
- Both subnet masks are
- Both PCs do not have any hard-coded IP specs in them.  All dynamic.
- I'm sure both are receiving their DHCP info from the Router as I changed the address to and they follow suit.
- DHCP now set to - 5 thru 10  (PC1 gets 5, PC2 gets 6)

- Changed IP addresses to, DHCP 5 thru 10
PC1 now
PC2 now

No change in behaviour.  Still can't consistently access the internet from both, and whenever I turn PC1 on, I have to recycle the modem, router, and PC1 to get on the internet from PC1.

I also changed network cards in PC2 with no change.  PC2 is the flakiest, ever since the change from it being a sub-network, to being on its own.
Both subnet masks are

I forget how to AND IPs and subnet masks together to get the complete subnet information.

Bottom line, no progress so far.


Author Comment

ID: 9664427
I meant whenever I turn PC2 on, PC1 loses its connection.
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Accepted Solution

RadRichie earned 0 total points
ID: 9664629
I installed the latest firmware for the router, reset it as per the firmware install instructions, and let it stay at the default, with DHCP using 100-whatever.  Both PCs can access the internet fine now.

I had reset teh router many times before with no luck.  Not sure if the firmware upgrade fixed the real culprit or not.

Expert Comment

ID: 9664663
OK, - never say die ;-)

You have isolated the most consistently failing component to be PC2, - and I expect you have already tried swapping network cables between the two machines ;-)

When you turn on PC2 and loose internet connection from both:
 - can you ping PC1 from PC2 and vice versa ?
 - does the LED's on the adapters or the router show activity ?

Re. PC2: what OS is it running ? have you installed antivirus ?

Author Comment

ID: 9664995
Yes, everything is working perfectly now.  Both on W2K Pro.

Expert Comment

ID: 9665251
Great ! Sounds like a router issue.

I've not been getting some emails from EE when comments have been added. So I didn't know comments were added for this question till now.

Since you've solved the problem yourself. You could post a request under Community Support to PAQ this question and refund your points back.

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