[Dnsmasq-discuss] "no address range available for DHCP request via br0" when using for IPv6 RA

[Simon Kelley]

On 03/04/2023 16:54, Ben Hendin wrote:
> I'm running Dnsmasq version 2.85-openssl-5-g989ee98 on an embedded 
> device (Entware installation)
> 
> I am seeing log entries that state the following when clients come onto 
> the network to request IP addresses via DHCP:
> 
> "no address range available for DHCP request via br0"
> 
> br0 is a bridged interface that includes the LAN and main WiFi of the 
> embedded device.
> 
> The issue is that I do not use dnsmasq on this device for DHCP on this 
> interface.
> (I do have it configured to deliver dhcp-range information to some other 
> wireless interfaces.)
> The main function on this interface is DNS and to deliver RAs for IPv6.
> 
> It appears, in order to deliver RAs to my clients the following lines 
> must be configured:
> 
> -------------------
> interface=br0
> ra-param=br0,10,600
> enable-ra
> dhcp-range=lan,::,constructor:br0,ra-stateless,64,600
> -----------------------
> 
> In other words, dhnsmasq must be configured to deliver the "dhcp-range" 
> option in order to deliver RAs (enable-ra isn't enough)
> Because of this you can't use the "no-dhcp-interface=br0" option or else 
> the dhcp-range and therefore the RA will not get delivered to clients.
> 
> When a client joins the network, it requests an IPv4 address, which will 
> not be served by dnsmasq, but by another authoritative server on the 
> network.
> However, because dnsmasq is configured to provide DHCP services, yet has 
> no IPv4 range defined it spits out the "no address range available"
> 
> I have tried changing the "ra-stateless" option to "slaac" or "ra-only" 
> as the description of "ra-only" seems to indicate that dnsmasq will then 
> be made aware it is only to deliver RAs and not DHCP (though perhaps 
> this only registers for v6).  I have also tried to use "quiet-dhcp" to 
> suppress these unsuccessfully.   Because the message is still logged, it 
> would fall under "error or problem" according to "quiet-dhcp" 
> specifications.
> 
> Is this behavior expected?  If so, is it considered preferable or should 
> dnsmasq have some configuration where it should not assume that an IPv4 
> range being unconfigured is an issue worth notifying about in scenarios 
> like this?
> 

That's not expected behaviour. The log does indeed imply that this is a 
DHCPv4 request (it would say no address range available for DHCPv6) but 
unless there's a valid IPv4 dhcp-range defined dnsmasq should not even 
be listening on the DHCPv4 port. The current code doesn't, and I don't 
remember any fixes to this the 2.85-2.89 timeframe.

What does dnsmasq log when it starts up? The most obvious explantion for 
this is that Entware's startup is defining a DHCPv4 range somewhere in 
the config that gets passed to dnsmasq.


Cheers,

Simon.


> thank you
> 
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