[Dnsmasq-discuss] DHCP packet received on <interface> which has no address

Andrew Shadura andrew.shadura at collabora.co.uk
Thu Aug 25 11:32:56 BST 2016

On 25/08/16 13:26, Andrew Shadura wrote:
> Okay, let me give you a more specific example, with just one of the
> interfaces.
> Let's say we've got eth0 with vlans:
>   eth0.1, static config
>   eth0.2, static config + dhcp server
>   eth0.3, dhcp client

So, let's say we've configured eth0.1 and eth0.2, then started dnsmasq.
 It complains eth3.4 (an interface expected on a different machine)
doesn't exist, so it'll skip and ignore it, and then it starts listening
on eth0.2.

Next, we bring eth0.3 up. DHCP client starts, and then dnsmasq starts
complaining it's received a DHCP packet on eth0.3 it didn't expect.

As I can see in the code, the first thing dnsmasq does for a packet
received on some interface is that it attempts to determine the
interface address. If that fails, none of the checks, which are further
down in the code, are performed.

> Interfaces may or may not be brought up on boot, or may be brought up on
> demand by the user. Some of the machines have a different set of
> interfaces, and we ship a universal set of configuration files with
> configuation for all possible interfaces different machines have
> (interface names don't overlap).


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