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Re: Another "Forwarding loop detected" issue

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On 05/11/2019 10:44, Amos Jeffries wrote:
On 5/11/19 10:40 pm, Nick Howitt wrote:
I am trying to help someone who is running squid-3.5.20-12 on a
standalone server with the dansguardian content filter and suddenly
recently has been getting a lot of messages like:

    2019/10/31 13:48:14 kid1| WARNING: Forwarding loop detected for:
    HEAD / HTTP/1.0
    Via: 1.0 HSFilterHyperos7.haftr.local (squid/3.5.20)
    Cache-Control: max-age=259200
    Connection: keep-alive
    X-Forwarded-For: 10.10.1.2
    Host: 10.10.1.2:8080


The access log looks something like:

    1572545946.383 120000 10.10.1.2 TCP_MISS_ABORTED/000 0 HEAD
    http://10.10.1.2:8080/ - HIER_DIRECT/10.10.1.2 -
    1572545946.477 120000 10.10.1.2 TCP_MISS_ABORTED/000 0 HEAD
    http://10.10.1.2:8080/ - HIER_DIRECT/10.10.1.2 -
    1572545946.493 120000 10.10.1.2 TCP_MISS_ABORTED/000 0 HEAD
    http://10.10.1.2:8080/ - HIER_DIRECT/10.10.1.2 -

(but these are for different transactions - they are all the same apart
from the timestamps)

That is what a forwarding loop looks like in the access.log.


The content filter listens on port 8080 and squid on 3128. The machine
is on 10.10.1.2

All the other posts I've seen seem to be for transparent mode or where
there is a User Agent string. I have found nothing to cover this
scenario. How can I troubleshoot to fix it and what information do you
need from me to help diagnose?

Something is telling Squid the origin server being contacted exists at
10.10.1.2:8080. You can see that in the Host header of the message.

I would trace the traffic flow from the client to Squid.

But isn't everything coming to 8080 as that is the proxy you'd set up in the browser? I'm afraid I don't understand how proxying works at the packet level. I see nothing before these messages to indicate the packets are coming from elsewhere. A cut down startup log looks like:

   <snip>
   2019/10/31 13:47:40 kid1| helperOpenServers: Starting 5/5
   'ext_unix_group_acl' processes
   2019/10/31 13:47:40 kid1| HTCP Disabled.
   2019/10/31 13:47:40 kid1| Finished loading MIME types and icons.
   2019/10/31 13:47:40 kid1| Accepting HTTP Socket connections at
   local=[::1]:3128 remote=[::] FD 2021 flags=9
   2019/10/31 13:47:40 kid1| Accepting HTTP Socket connections at
   local=127.0.0.1:3128 remote=[::] FD 2022 flags=9
   2019/10/31 13:47:40 kid1| Accepting HTTP Socket connections at
   local=10.10.1.2:3128 remote=[::] FD 2023 flags=9
   2019/10/31 13:48:12 kid1| WARNING: Forwarding loop detected for:
   HEAD / HTTP/1.0
   Via: 1.0 HSFilterHyperos7.haftr.local (squid/3.5.20)
   Cache-Control: max-age=259200
   Connection: keep-alive
   X-Forwarded-For: 10.10.1.2
   Host: 10.10.1.2:8080


   2019/10/31 13:48:14 kid1| WARNING: Forwarding loop detected for:
   HEAD / HTTP/1.0
   Via: 1.0 HSFilterHyperos7.haftr.local (squid/3.5.20)
   Cache-Control: max-age=259200
   Connection: keep-alive
   X-Forwarded-For: 10.10.1.2
   Host: 10.10.1.2:8080


Is there anything I can look for in my logs or do I need to do some sort of tcpdump with some filters?

Thanks,

Nick


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