[squid-users] Slow App through Proxy

Amos Jeffries squid3 at treenet.co.nz
Fri Dec 18 22:27:44 UTC 2015

On 19/12/2015 6:51 a.m., Kinkie wrote:
> Hi,
>   Do you see anything denied in the squid logs? From what you say it could
> be related to a failing attempt to validate a certificate.
> On Dec 18, 2015 17:25, "Patrick Flaherty" wrote:
>> Hello,
>> We have an app configured to use Squid Proxy (3.5.11). The client machine
>> does not have access to the internet except for the whitelisted domains in
>> Squid. The app launches painfully slow. It seems to be SSL Certificate
>> related. I found a way to fix it but don’t know why it fixes it. Let me
>> explain.
>> If I go into IE and configure it to use the Squid Proxy and I go to our
>> website (SSL Based), the page comes up fine with a nice lock symbol
>> signifying SSL. I then turn off the proxy config in IE to stop using the
>> Squid Proxy. I relaunch our app and it launches fast forever more!!! I
>> thought that it might be downloading a certificate but I look at all the
>> Windows certificates either through IE or CertMgr.msc and it appears that
>> no new certificates are in there after this exercise. Something in the
>> Windows config changed and I don’t know what it is. I would love to know
>> because I would like to see if there is an easier method to fix this as
>> opposed to the one I just outlined.

Several other things could have happened:
* HSTS headers from the server are received by the browser,
* Alternative-Protocol headers received by the browser,
* CRL and OSCP browser lookups without the proxy,
* or any combo of the above.

Alternative-Protocol is particularly bad since it can cause the browser
to move away from HTTP entirely and use some other protocol. Chrome has
a thing for moving traffic from HTTP to Google custom protocols. MSIE
should be pretty good though it might move to HTTP/2.

HSTS requires the browser to start directly with a secure protocol
rather than HTTP (ie through the proxy). When combined with
Alternative-Protocol the two could potentially force HTTP and the proxy
to cease being even considered as a traffic route (if browser thinks the
other protocol is more secure).

Since these happen inside the CONNECT tunnel use to go through an
explicit-proxy Squid does not have a chance to prevent the
Alternative-Protocol taking effect.

OSCP and CRL are annoying but friendly enough to proxy.  Just find out
what the needed URI are and ensure they are permitted through the proxy.


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