Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a device which runs a DHCP server. When I connect it with USB to my computer, the PC gets an IP address and the device becomes the default gateway. I just want the device to agree on IP addresses and not default gateway. Is this possible?

I was using udhcpd but I got problems with authoritative mode so I switched to dnsmasq.

The PC is already connected to another network witch should contain the default gateway.


Here is a little diagram of how it is setup

[ Embedded Network #1 ] ----- [ PC ] ----- [ Corporate Network #2 ]

What is important here is that Net#1 has no knowledge of Net#2, its dhcp server and its default gateway

EDIT 2 :

Ok, the parameter in /etc/dnsmasq.conf should be about dhcp-option=3
If I don't specify this parameter well, there is no effect. According to this example config.

# Disable default gateway

This does not disable the gateway, this has no effect

EDIT 3 :

ok dhcp-option=3 DOES have an effect (Silly me). However just renewing ip is not enough for windows xp to forget about the old one

share|improve this question

migrated from Jul 4 '11 at 13:57

This question came from our site for system and network administrators.

May I ask what did you do for Windows to forget about the old one? – sayap Sep 14 '12 at 4:14
Although being a little late, just for the reference, you can use ipconfig /release followed by a ipconfig /renew to make Windows forget about the old settings. – buergi Feb 23 '15 at 18:15
up vote 2 down vote accepted

Certainly possible - just reconfigure the device to not hand out a gateway over DHCP.

You probably need to provide more information to get a useful response.

add to the conf file


3 disables default router (gateway) and 6 disables DNS

share|improve this answer
What kind of information? – user1190 Jul 4 '11 at 13:54
What's the device? Can you reconfig dhcp on it? Or is this enough? – MikeyB Jul 4 '11 at 13:55
It is a custom embedded device which runs linux. I can cross compile a lot of stuff for ARM for it. I can of course edit configs – user1190 Jul 4 '11 at 14:06
You need to change DHCP option 3 (Router) to point to your router. DHCP is often handled by the router, so is is usually to have the DHCP configuration to default the router setting to its address. – BillThor Jul 4 '11 at 14:10
Bill, I edited my question. The device network does not know the other network – user1190 Jul 4 '11 at 14:16

I'm not sure if dnsmasq will operate the way you want. I use isc-dhcp-server and although it's not the most lightweight DHCP server, if you leave out the option routers stanza, it won't hand out any information for the default gateway. I used to use udhcpd as well until I needed DHCP reservations.

You also might try configuring dnsmasq to hand out whatever IP your current default gateway as its default gateway as @BillThor suggested, or see what happens when you hand out

share|improve this answer signals configuration error. My device's default gateway is itself. Not totally sure about what this means... – user1190 Jul 4 '11 at 17:43

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.