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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.

EDIT :

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
#dhcp-option=3

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

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migrated from serverfault.com Jul 4 '11 at 13:57

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2 Answers

up vote 1 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

dhcp-option=3
dhcp-option=6

3 disables default router (gateway) and 6 disables DNS

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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
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up vote 1 down vote

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 0.0.0.0

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