[Dnsmasq-discuss] DHCPv6 only

Thu May 6 01:57:46 UTC 2021

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.

> On Apr 29, 2021, at 4:10 PM, Simon Kelley <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
>> 
>> 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> 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> 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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