Re: [squid-users] dns-related cache problem (squid 3.3.8)

From: Dash Four <>
Date: Wed, 09 Oct 2013 13:00:50 +0100

Amos Jeffries wrote:
> On 9/10/2013 9:39 a.m., Dash Four wrote:
>> I have the following problem: I use the "hosts" file to store static
>> address mappings, usually containing sites which use geo address
>> mapping (in other words, determine the ip address one is going to use
>> depending on the geographic region the request is made from). One
>> such site is youtube for example.
>> Squid caches web pages content from these sites, but when I change
>> the IP address in "hosts", squid is still using the old IP address
>> for some reason, even though I verified that the new mapping is used
>> by the system.
>> In such cases, I have to stop squid, wipe out the entire cache and
>> then restart squid in order for the new host->ip mapping to be used.
>> This can't be right!
>> What I presume is happening is that somewhere along the line, squid
>> is storing clear ip addresses in the cache (probably to speed up
>> serving page content requests) and then it does not check whether
>> that ip address has changed. If that is so, could this be fixed,
>> because the idea of me clearing the entire cache every time I change
>> one of the "hosts" mappings does not exactly appeal to me. Thanks.
> Sort of. Squid loads the hosts file contents into DNS result cache
> with an infinite TTL in order to provide a single lookup mechanism for
> any DNS entry and prevent remote lokups of those FQDN. These are only
> loaded on startup and reconfigure time.
Thanks Amos, but I am not sure what you describe above is actually

When the "hosts" file is updated, I tried to reload squid's
configuration (-k reconfigure), but that did not help as squid was still
trying to connect to the "old" ip address. I then stopped (-k shutdown)
and then started squid without touching the existing cache - again,
squid was still referring to the old host->ip mapping.

The only way I "fixed" this is when I shutdown squid, delete the entire
cache and then start it - only then the correct host->ip mapping was
used, which would suggests that squid keeps the "old" ip addresses
somewhere, I presume in the cache. I should also say this: the incorrect
host->ip mapping is (mainly) used to retrieve secondary links (not main
page urls), which appear as links on the main web pages.

I initially thought that my web browser cache is to blame, but this was
eliminated as a possibility since I manually wiped out the entire web
browser cache and restarted the browser and still got the "old" mapping.

> Squid at this time does not yet have any mechanism for watching the
> file for changes (patches welcome!).
> If your OS supports a filesystem trigger feature such as inotify or
> dnotify you can script up a restart of Squid when hosts changes.
Yes, inotify is fully supported, but my issue is with squid caching dns
requests - that should not happen, or, at the very least, I should be
able to disable this behaviour. DNS-caching is the job of the DNS server
or, as in my case, the dnsmasq program I am using as dns resolver, not
Received on Wed Oct 09 2013 - 12:01:04 MDT

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