View Full Version : DSL Networking Connundrum

17th January 2003, 19:09

I have a DSL connection - my modem is a router, and serves DHCP. My PC is set up to obtain an address automagically.

The guy next door ALSO has a DSL connection - same deal.

We ran a wire through the wall (yeah, we're geeks) to save us from burning cd's for each other all the time.

Now, here's the trouble.

If we plug into a switch, we will get DHCP conflicts... two DHCP servers on the same physical network is bad, isn't it?

I've got mine set up on address, and it's serving up IP's in the 192.168.42.x range.

His is set to serve up IP's in the 192.168.254.* range, and it's running on IP

Is there any way to tell XP where to find the DHCP server? I'm not aware of one...

- Gurm

17th January 2003, 19:19
No, DHCP can't do that kind of deal, as far as I'm aware. With DHCP, the client has to be completely ignorant of the network. It says, "Hi, I'm with MAC address blahblahblah. Please help."

Although, here's two ideas that might work:

1. Set your DHCP lease time really high. I've seen weeks, longer should be possible. Then, have his modem off when you re-lease your IP, and vice-versa. They shouldn't ask again for a long time.

2. DHCP servers can use MAC addresses to accept/deny machines. If each of your computers get denials from the other guy's machine, you should be all right.

Edit: I like idea #2 better, personally.

17th January 2003, 19:31
Put a second NIC in each computer, and just run a second independant peer-peer through a crossover cable/adapter.

17th January 2003, 19:44
Yeah, we're tempted to do that Kruzin.

Wombat - I'd love it if these Speedstream 5667's had MAC address accept/deny, but they don't. :(

- Gurm

17th January 2003, 19:46
Do your IPs change? I've had the same IP for as long as I've had cable. DHCP is just handy when they expand the network.

Why not just set the NIC static?

17th January 2003, 19:48

'Cuz the modem won't talk unless you've asked it for an IP.

See how much of a pain this is?

- Gurm

17th January 2003, 19:56
Wow, a strange beast you've got there. I'm reading about it now:


It looks like maybe you can set it to "bridge mode."

18th January 2003, 12:58
Can you get the dhcp servers to give a certain ip address to a mac address, always to aa:bb:cc:dd:ee:ff to ff:ee:dd:cc:bb:aa
etc ...

This way there will never be an ip/subnet issue on your net.

Is this legal? Your ISP may have something to say
You are running on copper cables, I would check the electrical resistance of both properties, I wouldn't want one of you becoming earth. At work we are not allowed to run copper from buiding to building, only fibre as this is not a conductor.


20th January 2003, 03:39
Originally posted by Kruzin
Put a second NIC in each computer, and just run a second independant peer-peer through a crossover cable/adapter.

or simply set up XP with a second IP (static) for the NIC.

20th January 2003, 05:05
Yeah, I decided to just put the linux box in the closet with 2 nics. It's easier that way. It can then be a gateway box.

- Gurm

P.S. It's the next apartment, not the next building. So no worries about ground. Plus this place is so poorly built that NOTHING is grounded.

P.P.S. I wish we could make the modems do DHCP to certain MACs but it's a feature that's suspiciously absent from the Speedstream 5667. Bleh.

20th January 2003, 05:58
There's an option in the Linksys router that lets you operate two routers on teh same network without having said conflicts. I haven't used a router in a while...but it's somewhere in the Advanced tab. The option basically blocks out DHCP requests to other routers, if I remember the description correctly...

I'd look it up, but Linksys.com seems to be down, at least here, right now.