[Dnsmasq-discuss] Restrict DHCP providing default gateway to *one* host on one network

[Simon Kelley]

On 24/04/13 15:52, Will Dennis (Live.com) wrote:
> OK, this works - thanks TJ&  Simon!
>
> So as I understand it, the line:
> dhcp-option=tag:vl20-ovsbr0,tag:wanem-20,3
> means: for the machines tagged "vl20-ovsbr0" (which includes the WANem
> machine's 2nd NIC), just use whatever the default option would be for the
> router; but on machines tagged "wanem-20" (which matches ONLY the WANem
> machine's 2nd NIC), set a NULL router option.
> Correct? And, does order of application matter, or how else does dnsmasq
> resolve the two options that match for the WANem VM's 2nd NIC?
>

dhcp-option=tag:vl20-ovsbr0,tag:wanem-20,3

says, send an empty option 3 for hosts when vl20-ovsbr0 AND wanem-20 are 
set. What you should have is

dhcp-option=tag:vl20-ovsbr0,tag:!wanem-20,3

which says send an empty option 3 for hosts when vl20-ovsbr0 is set AND 
wanem-20 is NOT set.

Since option 3 is in the set of options which dnsmasq sends by default, 
the meaning of "send an empty option 3" is subtly altered to "don't send 
option 3"


Cheers,

Simon.

> Thanks again to everyone for their help in this!
>
> Best,
> Will
>
> -----Original Message-----
> From: dnsmasq-discuss-bounces at lists.thekelleys.org.uk
> [mailto:dnsmasq-discuss-bounces at lists.thekelleys.org.uk] On Behalf Of Simon
> Kelley
> Sent: Wednesday, April 24, 2013 5:01 AM
> To: dnsmasq-discuss at lists.thekelleys.org.uk
> Subject: Re: [Dnsmasq-discuss] Restrict DHCP providing default gateway to
> *one* host on one network
>
> On 24/04/13 08:58, TJ wrote:
>> On 23/04/13 15:33, Will Dennis (Live.com) wrote:
>>> interface=vl10-ovsbr0
>>> interface=vl20-ovsbr0
>>> bind-interfaces
>>> dhcp-range=vl10-ovsbr0,192.168.10.50,192.168.10.150,4h
>>> dhcp-range=vl20-ovsbr0,192.168.20.50,192.168.20.150,4h
>>> dhcp-host=52:54:00:d5:ee:4d,id:*,192.168.10.1
>>> dhcp-mac=set:wanem-20,52:54:00:45:8c:6a
>>> dhcp-option=vl10-ovsbr0,3,192.168.10.254
>>> dhcp-option=tag:vl20-ovsbr0,tag:!wanem-20,3,192.168.20.254
>>> log-dhcp
>>
>> I may be mis-reading the manual but as I understood it dnsmasq will
>> issue a default set of options for each range.
>>
>> dhcp-range=vl20-ovsbr0 will get a default option 3 which will be the
>> IP of the host running dnsmasq
>>
>> dhcp-mac=set:wanem-20 sets a tag for the exceptional client
>>
>> dhcp-option=tag:vl20-ovsbr0,tag:!wanem-20 will set a (possibly different)
> gateway for non-exceptional clients.
>>
>> At this point the exceptional client will have the default option 3 for
> the range. I think what you need is to not send any default route at all
> when the exceptional client makes a request:
>>
>> dhcp-option=tag:vl20-ovsbr0,tag:wanem-20,3
>
> I concur. Will, you've just omitted the empty option 3 from the last
> dhcp-option.
>
> (Wanders off to teach dnsmasq to complain in this situation.......)
>
>
> Cheers,
>
> Simon.
>
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