[avahi] Hostname case-sensitivity

[John McCabe]

Thank you for that - I will take a look with Wireshark when I next get 
round to 'playing' with it :-)

John


On 09/08/2023 14:40, Esko Dijk wrote:
> In my case the "ping" worked using different upper/lower-case combinations to find a lower-case hostname, on Ubuntu 22.04.2, with avahi 0.8.  (I didn't try yet using different combinations to find a UPPER-case hostname.)
> When I disabled avahi-daemon on the PC, doing such a ping for the .local domain automatically enables the daemon again.
>
> One side thought: When capturing the mDNS traffic with Wireshark it's also good to keep an eye on what the mDNS responder actually sends back as Answer: it can send either the actual hostname (e.g. all lowercase) or it could send the exact name that was queried (i.e. copied from the DNS Question label in the mDNS query packet.)
> Maybe some clients are sensitive as to what the responder sends back; and maybe some responders have a different policy of what they send back.  From what I saw at least Avahi 0.8 sent back the actual hostname (e.g. lowercase) in response to a query with mixed case or UPPER-case.
> There's some online discussion on this topic e.g. https://serverfault.com/questions/759934/can-dns-response-answers-be-in-a-different-case-than-the-query
>
> Esko
>
> -----Original Message-----
> From: avahi <avahi-bounces at lists.freedesktop.org> On Behalf Of John McCabe
> Sent: Wednesday, August 9, 2023 14:31
> To: avahi at lists.freedesktop.org
> Subject: Re: [avahi] Hostname case-sensitivity
>
> Hi Esko,
>
> Thank you for your reply and the reference to rfc6762. Interestingly, a
> short while after sending my message, pings to lower-case versions
> worked; I'm not sure why, although I did do avahi-browse -a in between.
>
> It's intriguing; I'm going to experiment with this embedded build to see
> if I can work out more about what's happening.
>
> Best Regards
>
> John
>
>> Hi,
>>
>> See mDNShttps://datatracker.ietf.org/doc/html/rfc6762#section-16  and RFC 4343 that clarifies in more detail.
>> So the hostnames must be treated case-insensitive.
>>
>> Personally I'm not aware of what changed between these versions.
>>
>> Esko
>>
>> -----Original Message-----
>> From: avahi <avahi-bounces at lists.freedesktop.org  <https://lists.freedesktop.org/mailman/listinfo/avahi>> On Behalf Of John McCabe
>> Sent: Tuesday, August 8, 2023 14:23
>> To:avahi at lists.freedesktop.org  <https://lists.freedesktop.org/mailman/listinfo/avahi>
>> Subject: [avahi] Hostname case-sensitivity
>>
>> Hi,
>>
>> I couldn't find this already being addressed, so thought I'd ask. I've
>> been using an embedded Linux image built with Avahi 0.6.32 for some time
>> now, and have had a go trying to build the same image with 0.8. I've
>> been successful, and it seems to work, but I'm seeing that, if I ping a
>> host, e.g. abc-123456.local, it's failing, but pinging ABC-123456.local
>> is fine.
>>
>> This wasn't the case with 0.6.32; has something changed in that area, or
>> is there anything that I may be missing?
>>
>> Thanks
>>
>> John
>>
>