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DWilliams
Asked: 2009-08-26 07:11:24 +0800 CST

Is there any way to prevent DHCP server conflicts?

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When I ordered the internet connection for work, they threw on a "bonus" router. It's a a 2wire gateway "every service we can cram in a box" type of thing. This is not what I preferred to work with, but seeing as how my company has a limited budget, I get to use what costs the least.

Now, the thing works fine for what I want it to (a pppoe device/router/gateway), but it throws in some extra features that I don't like. Most specifically, it includes a DHCP server and does not allow for any configuration of said server. I want to run the DHCP service on one of my actual servers so I can have granular control over everything (specifically I want to do static assignments based on MAC addresses, this thing doesn't even let me so much as choose what ranges to use).

If I set up my dhcpd server alongside the gateway's built-in DHCP service, it is my understanding that they will conflict with each other and dish out IPs in an almost random fashion, which obviously isn't good. What are my options here? There is no way to disable the gateway's DHCP function (well, there is, but it also disables PPPoE which turns the thing into glorified paperweight).

So far, two ideas have come to my head:

  1. Somehow use my switch (managed hp procurve) to segregate off the gateway's port into another VLAN. I'm not even sure if this is possible, though. I know doing this will block DHCP requests from reaching the gateway (since as I recall DHCP requests are broadcasts which won't cross over to other VLANS), but is it valid to have the gateway for one LAN on a separate LAN?
  2. Buy a real DSL modem and get some linksys router that will support DD-WRT or some other firmware that allows for great customization. This costs money, however, and I need to conserve money wherever possible...

Does anyone have any more elegant solutions?

I searched and found a couple similar questions, but they all seemed to be dealing with intentionally having multiple DHCP servers and don't really have any good solutions for my problem.

router dhcp gateway

3 Answers

  1. Best Answer

    Look harder - you can disable the DHCP server on 2wire routers.

    What's the model number

    • 4

  2. You might want to look into the HP Procurve's DHCP snooping feature, there you can set an authorized DHCP server by IP and block any other DHCP offers. Here's a whitepaper on it, hope it helps and hope your switch supports this:

    http://h40060.www4.hp.com/procurve/uk/en/pdfs/application-notes/AN-S12_ProCurve-DHCP-snooping-final.pdf

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  3. can you put the 2wire gateway into bridged mode, so it's effectively just a dumb modem?

    if so, you could then run pppoe on a linux box, which could also run any other services you need like DHCP and DNS cache. this linux box would effectively be the gateway/firewall and would need two ethernet interfaces (or two vlans on one NIC), one to talk to the bridged modem and one to talk to the rest of the LAN.

    other than that, your idea of swapping the modem for one that can run dd-wrt is good.

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