[Dnsmasq-discuss] DHCPv6 only

Simon Kelley simon at thekelleys.org.uk
Thu May 6 08:03:40 UTC 2021



On 06/05/2021 02:57, Aaron Oneal wrote:
> DHCPv4 needs to be running on other interfaces because there are guest
> networks.
> 
> E.g.
> May  5 18:15:14 dnsmasq-dhcp[9209]: DHCP, IP range 192.168.203.2 --
> 192.168.203.254, lease time 1d
> May  5 18:15:14 dnsmasq-dhcp[9209]: DHCP, IP range 192.168.202.2 --
> 192.168.202.254, lease time 1d
> May  5 18:15:14 dnsmasq-dhcp[9209]: DHCP, IP range 192.168.201.2 --
> 192.168.201.254, lease time 1d
> 
> Nothing in the log clearly explains what interfaces those ranges are
> assigned to, but in the config they are br1, br2, br3.
> 
> The br0 interface does *not* have an IPv4 range configured and should be
> DHCPv6 only.
> 
> Yet, Dnsmasq is still receiving DHCPv4 messages on br0, processing, and
> spamming the log saying that a range isn’t configured.
> 
> 

Add

no-dhcp-interface=br0

to your config.


Cheers,

Simon.


>> On Apr 29, 2021, at 4:10 PM, Simon Kelley <simon at thekelleys.org.uk
>> <mailto:simon at thekelleys.org.uk>> wrote:
>>
>> On 24/04/2021 04:28, Aaron Oneal wrote:
>>> Geert, thank you that is a creative solution. I wasn’t able to
>>> determine how to configure that so I determined a way to change my
>>> network topology instead to work around.
>>>
>>> Simon, thank you for your assistance. Let me see if I can help track
>>> this down.
>>>
>>> Dnsmasq is listening on 67:
>>> udp        0      0 0.0.0.0:67
>>>                                          0.0.0.0:*
>>>                                                       PID/dnsmasq
>>>
>>> Nothing logged on startup in syslog other than:
>>> Apr 23 20:13:14 dnsmasq-dhcp[PID]: no address range available for
>>> DHCP request via br0
>>>
>>> ASUS router with this firmware:
>>> https://github.com/RMerl/asuswrt-merlin.ng
>>> <https://github.com/RMerl/asuswrt-merlin.ng>
>>>
>>> Dnsmasq version:
>>> Dnsmasq version 2.84-42-g433dc70  Copyright (c) 2000-2021 Simon Kelley
>>> Compile time options: IPv6 GNU-getopt no-RTC no-DBus no-UBus no-i18n
>>> no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset no-auth cryptohash
>>> DNSSEC no-ID loop-detect no-inotify no-dumpfile
>>>
>>> Line generating the error (rfc2131.c Line 345):
>>> https://github.com/imp/dnsmasq/blob/master/src/rfc2131.c
>>>
>>>
>>
>> By far the simplest explanation for this is that the dnsmasq config is
>> enabling DHCPv4. If the Asus firmware is anything like OpenWRT, it will
>> do all sorts of stuff behind the scenes. Before doing anything else, we
>> need to find out what dnsmasq is reporting as its config. The easiest
>> way to do that might be to redirect all the dnsmasq logging to a file
>> using something like
>>
>> log-facility=/path/to/file
>>
>> and then restart dnsmasq (if you can) or reboot the whole system.
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>
>>>> On Apr 23, 2021, at 10:48 AM, Simon Kelley <simon at thekelleys.org.uk
>>>> <mailto:simon at thekelleys.org.uk>> wrote:
>>>>
>>>> On 21/04/2021 19:41, Aaron Oneal wrote:
>>>>> I am trying to configure my gateway running Dnsmasq to serve IPv6
>>>>> addresses via SLAAC+RA and I don’t see how to enable that in a way
>>>>> that doesn’t also require IPv4 DHCP to be turned on.
>>>>>
>>>>> interface=br0
>>>>> dhcp-range=lan,::,constructor:br0,ra-stateless,64,600
>>>>> ra-param=br0,10,600
>>>>> enable-ra
>>>>>
>>>>> I already have a different server on the LAN that handles IPv4 DHCP
>>>>> so I don’t want Dnsmasq doing it.
>>>>>
>>>>> The problem is, Dnsmasq listens on IPv4 anyway and every time it
>>>>> receives an IPv4 DHCP message it spams my syslog with dozens of
>>>>> messages per second saying "no address range available for DHCP
>>>>> request via br0." I didn’t specify an IPv4 range because I don’t
>>>>> want one.
>>>>>
>>>>> I tried using `listen-address=<ipv6 addresses>` instead of
>>>>> `interface=br0` but then RA doesn’t seem to be active and my
>>>>> devices stop receiving IPv6 addresses.
>>>>>
>>>>> I can’t remove the IPv4 address from the interface because it’s a
>>>>> gateway.
>>>>>
>>>>> Is there a way to configure Dnsmasq for IPv6 only?
>>>>
>>>>
>>>> What you're doing should configure dnsmasq for IPv6 only, and a naive
>>>> attempt to reproduce you setup doesn't seem to have the same problem.
>>>> It's certainly not listening on IPv4 UDP port 68, which it would be if
>>>> serving DHCPv4.
>>>>
>>>> Please could you let us know what version of dnsmasq you are running,
>>>> and what it logs at start-up? That would help to reproduce the bug at
>>>> this end.
>>>>
>>>>
>>>> Simon.
>>>
>>>> On Apr 21, 2021, at 1:09 PM, Geert Stappers via Dnsmasq-discuss
>>>> <dnsmasq-discuss at lists.thekelleys.org.uk
>>>> <mailto:dnsmasq-discuss at lists.thekelleys.org.uk>> wrote:
>>>>
>>>> Path I would go is configuring dnsmasq to only IPv4 DHCP reply to known
>>>> MAC-addresses. And than have a MAC address configured that none of the
>>>> clients has.  No, I never have travelled that path. I do like to known
>>>> if it lead to the wanted goal.
>>>>
>>>>
>>>> Groeten
>>>> Geert Stappers
> 



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