cable modem knocks out LAN

[AlexGee]

The situation:

We start with 3 PC's (2 XP, 1 98) on a peer to peer LAN, hooked up through a Linksys 10/100 switch, IP addresses are assigned by us, i.e. we are not using DHCP. LAN is fully functional - we can share files and printers and also browse the network through network neighborhood.

Last night we added Comcast 'business' cable modem service, which comes with 5 IP addresses. We hook up modem to switch and make one change only to network seetings; we tell each PC to obtain IP automatically so that they can pick up their IP through Comcast. Immediately each PC can surf the web just fine BUT now our LAN is not working. We cannot see shared files or drives, we cannot map or browse through network neigh., nor can we print to network printers.

One last bit of info: For a short time it was all working properly, i.e. LAN and web surfing were working at same time. We have no idea why. Any help is greatly appreciated! Thanks.

[BipolarBill]

Have you checked the IPs that were assigned to each PC? Use WINIPCFG in Win9x and IPCONFIG from a command prompt in NT.

You may have been assigned different subnet masks. Here's is where a router has it all over multiple IPs.

[Midknyte]

Like BPB said, you should invest in a router. you can use dhcp from the router so that your systems will all have the same ip range, subnet mask, dns, etc. ISPs will always subnet your connections, so there is no guarantee that your systems will all be in the same group.

does your ISP give you static IPs? if so, maybe they were typed in wrong.

you would also benefit from the protection of the built-in firewall that many routers have.

on top of all that, the router will pay for itself in the long run. instead of paying for 5 IPs, you just need 1. :)

[AlexGee]

Thanks much for the response. Will be back at office in a day or so to check the addresses. Probly get a router. Will report back.

[pandaz3]

I had a problem using hubs (linksys) and could not go past 3 computers on my "lan". Lucky for me a lightning strike took them out and I got a Linksys 8 port router. Now I have NO problems with 5 computers on line.:)

[AllGamer]

Originally posted by AlexGee
Thanks much for the response. Will be back at office in a day or so to check the addresses. Probly get a router. Will report back.

Alex, to make the long tech explanation short.

The reason why you can't do what you did again, is due the new IPs and DNS

before you was in a LAN enviroment

now you are in a WAN or Internet enviroment.

so your computers are currently WIDE open to any hacker that wants to get into them

best solution is to make it a LAN again, yet still have Internet connection, and the best way for that as Bill and Midnite has already pointed out is to get a ROUTER.

same setup, but is local.
the router will take care of the IP for you, and you really only need 1 IP from the ISP, no need to spend extra on additional IP addresses, that's normall $10 extra a month per IP #

[AlexGee]

Update:

Got a Linksys 4 port router/switch and all problems solved.

Added benifit: Now we don't have to put a firewall on each PC.

Thanks for the good advice.