OpenThread border router DNS - use domain directive from resolve.conf

[brown27]

I am using the border router's upstream DNS and $ sudo ot-ctl nat64 state shows that it is active. My Thread child device can resolve hosts like google.com without issue. The upstream DNS uses "iot-edge" as an alias for "pc7.ab.cd.com." However, if my child device does a DNS lookup for "iot-edge" using otDnsClientResolveIp4Address() it gets a "No such name error" as seen below.

Similarly, I get an NXDOMAIN error on my Raspberry Pi border router when I try $ dig iot-edge

However, the Pi is able to resolve "iot-edge" when I add the +search flag. This flag uses the search list defined by the searchlist or domain directive in resolv.conf

What setting am I missing in my border router's NAT64 setup to duplicate the +search flag's functionality and enable these alias lookups? Thank you in advance!

[Charlie]

Hi,

This may be related to the aConfig argument initialization on your codes.

Could you test the CLI DNS resolution commands similar to https://groups.google.com/g/openthread-users/c/6uYzwjk6VHo/m/KPgjb_3PCQAJ first with your OTBR as DNS server?

openthread/src/cli at main · openthread/openthread (github.com) has the source codes about how this command is implemented, which should show the process of aConfig initialization.

Best regards,

Charlie

[brown27]

I am currently sending DNS requests to the border router and using its upstream DNS server to fulfil requests. I have set up the border router as instructed here and use `otDnsClientResolveIp4Address()` on the Thread child to initiate these requests.

I think that I might want to use `$ sudo ot-ctl srp server domain [domain-name]` on the border router and `grep` the domain name from `/etc/resolv.conf`. Otherwise, the border router seems to use `default.service.arpa.` as the default domain. I will try this and report back on how it works.

[Charlie]

Thanks for the update!

[brown27]

Unfortunately `srp server domain [domain-name]` did not solve my issue. If my Thread child device does a DNS lookup for "example" it gets the following response:

"Standard query response 0xabcd No such name A example SOA a.root-servers.net"

However, `$ nslookup example` and `$ dig +search example` on the border router yield the desired IPv4 address. Is there anything else I should be trying or investigating?

[Charlie]

Hi,

I looked at the source codes from openthread github, it seems the upstream resolver is configured in prosix running on RPI. Could you follow the following discussion to check?

Update the list of upstream dns server when resolv.conf is modified · Issue #9021 · openthread/openthread (github.com)

Best regards,

Charlie