Hi,

> On 27 Jun 2024, at 10:17 AM, Riccardo Brunetti Host <riccardo.brunetti@host.it> wrote:
>
>
>
>> On 26 Jun 2024, at 17:56, Roman Arutyunyan <arut@nginx.com <mailto:arut@nginx.com>> wrote:
>>
>> Hi,
>>
>>> On 26 Jun 2024, at 7:21 PM, Riccardo Brunetti Host <riccardo.brunetti@host.it <mailto:riccardo.brunetti@host.it>> wrote:
>>>
>>> Hello, thanks for the answer.
>>>
>>>> On 26 Jun 2024, at 16:45, Roman Arutyunyan <arut@nginx.com <mailto:arut@nginx.com>> wrote:
>>>>
>>>> Hi,
>>>>
>>>>> On 26 Jun 2024, at 6:15 PM, Riccardo Brunetti Host <riccardo.brunetti@host.it <mailto:riccardo.brunetti@host.it>> wrote:
>>>>>
>>>>> Hello.
>>>>>
>>>>> I have a Nginx server which acts as a reverse proxy for a given number of different domains and I’m trying to enable http3 for a subset of them.
>>>>>
>>>>> I placed the directives:
>>>>>
>>>>>> http3 on;
>>>>>> listen xx.xx.xx.xx:443 default_server quic reuseport;
>>>>>> quic_retry on;
>>>>>
>>>>> in the default.conf file and then, only for those domains which I want http3 enabled I also add in the corresponding virtual host:
>>>>>
>>>>>> http3 on;
>>>>>> listen xx.xx.xx.xx:443 quic;
>>>>>> quic_retry on;
>>>>>
>>>>> In the server section and
>>>>>
>>>>>> add_header Alt-Svc 'h3=":8443"; ma=86400';
>>>>>
>>>>> Inside the location.
>>>>>
>>>>> Now, what happens is that if I try to open the sites *with* http3 enabled, everything works as expected. If I try to open a site *without* http3 enabled, sometimes I have an SSL error because the server returns the “default virtual host” certificate.
>>>>> It seems related to the type of browser.
>>>>>
>>>>> Is it an expected behaviour or I am doing something wrong with the server configuration?
>>>>
>>>> If you use http/3 to access a virtual server that does not support http/3, the default http/3 server will be used.
>>>>
>>>> Make sure the above add_header does not affect the servers which do not support http/3.
>>>
>>> I add the header above only on the virtual hosts which I want to support http/3, thus it should not interfere with the other non http/3 domains.
>>> Nevertheless, if I try with curl:
>>>
>>> 1) Site http/3 enabled:
>>>
>>>> # curl --http3 -I -v https://<fqdn>
>>>> * Host <fqdn>t:443 was resolved.
>>>> * IPv6: (none)
>>>> * IPv4: <ip>
>>>> * WARNING: no socket in pollset, transfer may stall!
>>>> * Trying <ip>:443...
>>>> * Server certificate:
>>>> * subject: CN=<fqdn>
>>>> * start date: May 14 07:39:37 2024 GMT
>>>> * expire date: Aug 12 07:39:36 2024 GMT
>>>> * subjectAltName: host “<fqdn>" matched cert's “<fqdn>"
>>>> * issuer: C=US; O=Let's Encrypt; CN=R3
>>>> * SSL certificate verify ok.
>>>> * Connected to <fqdn> (<ip>) port 443
>>>> * using HTTP/3
>>>> * [HTTP/3] [0] OPENED stream for https://<fqdn>/
>>> …
>>> …
>>>
>>> So it gets the correct certificate and it goes on using http/3
>>>
>>> 2) Site non http/3 enabled:
>>>
>>>> # curl --http3 -I -v https://<fqdn>
>>>
>>>> * Host <fqdn>:443 was resolved.
>>>> * IPv6: (none)
>>>> * IPv4: <ip>
>>>> * WARNING: no socket in pollset, transfer may stall!
>>>> * Trying <ip>:443...
>>>> * SSL certificate problem: unable to get local issuer certificate
>>>> * connect to <ip> port 443 failed: SSL peer certificate or SSH remote key was not OK
>>>> * Failed to connect to<fqdn> port 443 after 33 ms: SSL peer certificate or SSH remote key was not OK
>>>> * Trying <ip>:443...
>>>> * Connected to<fqdn> (<ip>) port 443
>>>> * ALPN: curl offers h2,http/1.1
>>>> * TLSv1.2 (OUT), TLS handshake, Client hello (1):
>>>> * TLSv1.2 (IN), TLS handshake, Server hello (2):
>>>> * TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
>>>> * TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
>>>> * TLSv1.3 (IN), TLS handshake, Certificate (11):
>>>> * TLSv1.3 (IN), TLS handshake, CERT verify (15):
>>>> * TLSv1.3 (IN), TLS handshake, Finished (20):
>>>> * TLSv1.3 (OUT), TLS handshake, Finished (20):
>>>> * SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 / [blank] / UNDEF
>>>> * ALPN: server accepted h2
>>>> * Server certificate:
>>>> * subject: CN=<fqdn>
>>>> * start date: Apr 16 08:36:25 2024 GMT
>>>> * expire date: Jul 15 08:36:24 2024 GMT
>>>> * subjectAltName: host "<fqdn>" matched cert's "<fqdn>"
>>>> * issuer: C=US; O=Let's Encrypt; CN=R3
>>>> * SSL certificate verify ok.
>>>> * using HTTP/2
>>>> * [HTTP/2] [1] OPENED stream for https://<fqdn>/
>>>
>>>
>>> So it tries with http/3, gets a wrong certificate (the server default one), then it switches to http/2 and goes on.
>>> The first attempt with http/3 probably gives problems with some browsers?
>>> If this is the case, is there a way to avoid this or should I simply configure http/3 on all domains?
>>
>> Why would you (or client) connect to an http/3 port for a server which does not support http/3?
>> What would be your expectation in this case? The same will happen for http/1 and http/2 as well.
>> You can connect to an http/1 ssl port, request a missing server and receive a default server certificate.
>> It's just there is no fallback for http/1 and client will just give up.
>>
>> The add_header suggests that http/3 is supported for a certain server.
>> It should not be sent for servers which do not support http/3, and clients should not use http/3 for them.
>
> I agree with you, mine was an example just to show with curl what seems to happen with some browsers.
> It seems to me that they try http/3 even if the server doesn’t advertise the header and then stop because of the error on the certificate.
> I don’t know if this is something known.
> Anyway, I think I will bypass this by enabling http/3 on all sites.

One more thing you can do is to reject handshake for default server:

https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_reject_handshake

>
> Thanks a lot for you help
>
> Riccardo
>
>>
>>>> If it does, this will mislead clients by offering them to switch to unsupported http/3.
>>>>
>>>>> Nginx version: nginx/1.26.1 on ubuntu 22.04
>>>>>
>>>>> Thanks.
>>>>> Riccardo
>>>>> _______________________________________________
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>>>>
>>>> ----
>>>> Roman Arutyunyan
>>>> arut@nginx.com <mailto:arut@nginx.com>
>>>>
>>>
>>> Riccardo
>>>
>>>>
>>>>
>>>>
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>>
>> ----
>> Roman Arutyunyan
>> arut@nginx.com <mailto:arut@nginx.com>
>>
>>
>>
>>
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----
Roman Arutyunyan
arut@nginx.com




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