You do realize that there's nothing "weird" about p0f, right? Perhaps you should have a read over:
On Mon, Oct 30, 2017 at 11:22 AM, Alex Rousskov <rousskov@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
On 10/30/2017 03:51 AM, Troiano Alessio wrote:
> I've squid 3.5.20 running on RHEL 7.4. I have a problem to access
> some websites, for example www.nato.int. This website apply an
> Anti-DDoS system that reset the first connection after the TCP 3-way
> handshake (SYN/SYN-ACK/ACK/RST-ACK). All subsequent TCP connections
> are accepted. The website administrator say's it is by design.
> When I browse the site with squid proxy the browser receive an "Empty
> Response" squid error page (HTTP error code 502 Bad Gateway) and
> doesn't do the automatic retry:
This is by design as well :-).
We can change Squid behavior to retry connection resets, but I am sure
that some folks will not like the new behavior because in _their_ use
cases a retry is wasteful and/or painful. IMHO, the new behavior should
be controlled by a configuration directive, possibly an ACL-driven one.
Quality patches implementing the above feature should be welcomed IMO.
The tip of the relevant code is probably in ERR_ZERO_SIZE_OBJECT
handling inside FwdState::fail(). There is a similar code that handles
persistent connection races there already, but the zero-size reply code
may need a new dedicated FwdState flag to prevent infinite retry loops
when the origin server is broken (a much more typical use case than the
weird attempt at DDoS mitigation that you have described above).
https://wiki.squid-cache.org/SquidFaq/AboutSquid#How_to_ add_a_new_Squid_feature.2C_ enhance.2C_of_fix_something.3F
HTH,
Alex.
> [root@soc-pe-nagios01 ~]# wget www.nato.int -e use_proxy=yes -e http_proxy=172.31.1.67:8080
> --2017-10-30 10:41:09-- http://www.nato.int/
> Connecting to 172.31.1.67:8080... connected.
> Proxy request sent, awaiting response... 502 Bad Gateway
> 2017-10-30 10:41:09 ERROR 502: Bad Gateway.
>
> I can't find an RFC that confirm if browser and proxyes should try a page reload, or if squid has an option to do that.
>
> Any help is appreciated.
>
> Best Regards, Alessio.
>
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