Hi,
I am running into a bug in the following circumstances.
When the config has a mix of the below (e.g. pick any 2 of 3, or pick
all 3):
1. dynamic-host entries with only IPv4 address fragments specified.
2. dynamic-host entries with only IPv6 address fragments specified.
3. dynamic-host entries with both IPv4 and IPv6 address fragments
specified.
Then the following occurs when querying DNS for PTR records:
* For IPv6 PTR records from dynamic-host, only IPv6 addresses whose
dynamic-host entries are before the first IPv4-only dynamic-host
entry can be resolved to name. All IPv6 addresses whose entry is
after the first IPv4-only entry cannot be resolved to name.
* For IPv4 PTR records from dynamic-host, only IPv4 addresses
whose dynamic-host entries are before the first
IPv6-only dynamic-host entry can be resolved to name. All IPv4
addresses whose entry is after the first IPv6-only entry cannot be
resolved to name.
The man page entry for dynamic-host shows both [IPv4-address] and
[IPv6-address] in square brackets [], suggesting that it's perfectly
acceptable to specify entries with only IPv4, only IPv6, or both
IPv4+IPv6. I haven't seen anything suggesting that they should not be
mixed and matched.
This seems vaguely similar to the issue fixed by commit
f4c87b504b444efb05892b8c7fc295e886f70789
<https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=f4c87b504b444efb05892b8c7fc295e886f70789> back
in February (I was originally testing with dnsmasq 2.85 before this fix
and ran into this issue myself). However I have confirmed this issue
using dnsmasq from the Git repo as of 2022-07-22 (on both Raspberry Pi
OS bullseye and Debian Sid) - well after this commit.
For context, the reason that I personally am running into this scenario
is because I am using dnsmasq for DHCPv6 and DNS. So I have:
(a) Some devices where I add a dhcp-host entry for IPv6 + a
dynamic-host entry for only IPv4.
(I would be using host-record instead of dynamic-host as my IPv4
prefix is fixed, but I'm currently using dynamic-host as a
workaround to another issue identified on this mailing list: With
auth-zone enabled, DNS response only provides DHCPv6 IP and ignores
IPv4 address/host-record entries
<https://www.mail-archive.com/dnsmasq-discuss@lists.thekelleys.org.uk/msg16336.html>)
(b) Other devices where I add a single dynamic-host entry for both
IPv4 and IPv6.
The first (a) entry breaks reverse lookup for all IPv6 addresses in (b)
entries.
PTR records added by other means work fine - for example from ptr-record
or dhcp-host. Therefore manually adding ptr-records is a workaround
(although very tedious for IPv6!)
More detail and steps to reproduce:
(0) Consider the configuration below, with a mix of IPv4-only and
IPv4+IPv6 entries:
no-resolv
dynamic-host=Computer1.example.org <http://Computer1.example.org>,
0.0.0.1, ::1, eth0
dynamic-host=Computer2.example.org <http://Computer2.example.org>,
0.0.0.2, eth0
dynamic-host=Computer3.example.org <http://Computer3.example.org>,
0.0.0.3, ::3, eth0
dynamic-host=Computer4.example.org <http://Computer4.example.org>,
0.0.0.4, eth0
dynamic-host=Computer5.example.org <http://Computer5.example.org>,
0.0.0.5, ::5, eth0
Assume the local network is 10.0.0.0/24 <http://10.0.0.0/24> and
fd50::/64, and eth0 is configured with IPs in these ranges.
(1) Looking up A records for all 5 names will return results for all 5
computers - as expected
$ dig @10.0.0.1 <http://10.0.0.1> +short A Computer1.example.org
<http://Computer1.example.org> Computer2.example.org
<http://Computer2.example.org> Computer3.example.org
<http://Computer3.example.org> Computer4.example.org
<http://Computer4.example.org> Computer5.example.org
<http://Computer5.example.org>
10.0.0.1
10.0.0.2
10.0.0.3
10.0.0.4
10.0.0.5
(2) Looking up AAAA records for all 5 names will return results for
Computer1, Computer3, and Computer5 - as expected
dig @10.0.0.1 <http://10.0.0.1> +short AAAA Computer1.example.org
<http://Computer1.example.org> Computer2.example.org
<http://Computer2.example.org> Computer3.example.org
<http://Computer3.example.org> Computer4.example.org
<http://Computer4.example.org> Computer5.example.org
<http://Computer5.example.org>
fd50::1
fd50::3
fd50::5
(3) Looking up PTR records for all 5 IPv4 addresses will return names
for all 5 computers - as expected
$ dig @10.0.0.1 <http://10.0.0.1> +short -x 10.0.0.1 -x 10.0.0.2 -x
10.0.0.3 -x 10.0.0.4 -x 10.0.0.5
Computer1.example.org <http://Computer1.example.org>.
Computer2.example.org <http://Computer2.example.org>.
Computer3.example.org <http://Computer3.example.org>.
Computer4.example.org <http://Computer4.example.org>.
Computer5.example.org <http://Computer5.example.org>.
(4) However, looking up PTR records for all 3 IPv6 addresses will
*only* return the name for Computer1. This is not expected - all three
names should be returned.
$ dig @10.0.0.1 <http://10.0.0.1> +short -x fd50::1 -x fd50::3 -xfd50::5
Computer1.example.org <http://Computer1.example.org>.
What is happening is the existence and position of the entry for
Computer2 is breaking reverse DNS lookup for Computer3/Computer5.
The behaviour is entirely affected by the order of the dynamic-host
entries in the file. For example, if you reverse the order of the
dynamic-host entries in the config in (0), then only the name for
Computer 5 is returned.
$ dig @10.0.0.1 <http://10.0.0.1> +short -x fd50::1 -x fd50::3 -x
fd50::5
Computer5.example.org <http://Computer5.example.org>.
If you change the order so all IPv4+IPv6 entries are first (i.e.
Computer1 > Computer3 > Computer5 > Computer2 > Computer4), then all
IPv6 addresses can resolve to names:
$ dig @10.0.0.1 <http://10.0.0.1> +short -x fd50::1 -x fd50::3 -x
fd50::5
Computer1.example.org <http://Computer1.example.org>.
Computer3.example.org <http://Computer3.example.org>.
Computer5.example.org <http://Computer5.example.org>.
If you change the order so all IPv4-only entries are first (i.e.
Computer 2 > Computer 4 > Computer 1 > Computer 3 > Computer 5), then no
IPv6 addresses can resolve to names at all.
$ dig @10.0.0.1 <http://10.0.0.1> +short -x fd50::1 -x fd50::3 -x
fd50::5
(5) For the reverse of (0)-(4) - a mix of IPv6-only and IPv4+IPv6
entries - the reverse problem occurs:
Config:
no-resolv
dynamic-host=Computer1.example.org <http://Computer1.example.org>,
0.0.0.1, ::1, eth0
dynamic-host=Computer2.example.org <http://Computer2.example.org>,
::2, eth0
dynamic-host=Computer3.example.org <http://Computer3.example.org>,
0.0.0.3, ::3, eth0
dynamic-host=Computer4.example.org <http://Computer4.example.org>,
::4, eth0
dynamic-host=Computer5.example.org <http://Computer5.example.org>,
0.0.0.5, ::5, eth0
IPv4 PTR records broken (only returns those before Computer2)
$ dig @10.0.0.1 <http://10.0.0.1> +short -x 10.0.0.1 -x 10.0.0.3 -x
10.0.0.5
Computer1.example.org <http://Computer1.example.org>.
(7) For a mix of IPv4-only and IPv6-only entries, the same problem
occurs for both:
Config:
no-resolv
dynamic-host=Computer1.example.org <http://Computer1.example.org>,
::1, eth0
dynamic-host=Computer2.example.org <http://Computer2.example.org>,
0.0.0.2, eth0
dynamic-host=Computer3.example.org <http://Computer3.example.org>,
::3, eth0
dynamic-host=Computer4.example.org <http://Computer4.example.org>,
0.0.0.4, eth0
dynamic-host=Computer5.example.org <http://Computer5.example.org>,
::5, eth0
IPv4 PTR records broken (only returns those before Computer1 - i.e. none)
$ dig @10.0.0.1 <http://10.0.0.1> +short -x 10.0.0.2 -x 10.0.0.4
IPv6 PTR records broken (only returns those before Computer2)
$ dig @10.0.0.1 <http://10.0.0.1> +short -x fd50::1 -x fd50::3 -x
fd50::5
Computer1.example.org <http://Computer1.example.org>.
Hope this is all clear!
Kind regards,
ryt51v
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