[Dnsmasq-discuss] interface+macvlan on same network confuses dnsmasq v2.66rc2
simon at thekelleys.org.uk
Tue Oct 22 19:20:07 BST 2013
On 22/10/13 17:17, Gui Iribarren wrote:
> On 10/22/2013 05:45 PM, Simon Kelley wrote:
>> On 21/10/13 20:31, Gui Iribarren wrote:
>>> Hello Simon!
>> My hunch is that this is something to do with ARP.
> indeed! i'm sorry i didn't provide tcpdumps
> you're right, instead of the expected DHCPOFFER, all i got on the client
> were endless ARP requests for the would-be-offered IP, coming from the
> so, what you're saying is that dnsmasq is prepopulating the ARP cache
> pointing to the wrong interface?
> # arp -a
> IP address HW type Flags HW address Mask Device
> 192.168.11.20 0x1 0x2 20:16:d8:65:4d:29 * br-lan
> that's on the router, just after asking for a lease from the client,
> with dnsmasq.conf containing no-dhcp-interface=br-lan
I don't think it's a simple as setting the wrong interface in the ARP
> Then, do you think there's any chance of getting that arp trick point to
Yes, depending on the results of the dhcp-broadcast thing.
> i'll try dhcp-broadcast later today
> what would be the downsides / cons of having dhcp-broadcast permanently
> enabled? maybe some broken clients?
Just a bit more load on clients from the broadcasts. Unless your network
is HUGE, I doubt it's noticable.
> thanks a lot!
>> For an unconfigured
>> client (ie doing DHCPDISCOVER) dnsmasq ends up knowing the MAC address
>> of the client and its IP address, but the client _doesn't_ know that IP
>> address, and so can't respond to a ARP request. To get round this,
>> dnsmasq populates the ARP table on the server directly with the IP
>> address, MAC address and interface. Then it send the OFFER packet to the
>> IP address and the kernel knows how to route it. I think that you
>> "interesting" setup may be confusing this process. In the second
>> instance, I suspect that the crucial thing that makes it work is not the
>> presence of a lease in the lease-file, but a correct ARP-table entry
>> from the previous activity.
>> Certainly, a few more experiments, and looking at the output of
>> arp -a
>> would be instructive.
>> Looking again - there are more clues:
>> ### the OFFER it's sending is a funny mix:
>> ### it is sent *from* br-lan MAC and IP (192.168.11.129)
>> That may be the MAC address thing I talked about, or it may be something
>> else. Another experiment: try setting
>> and see what happens then.
>> Dnsmasq-discuss mailing list
>> Dnsmasq-discuss at lists.thekelleys.org.uk
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