How to force using single parent?

Hi!

I would like to test some network performance and have convinced an
admin of a site near mine to allow me to use his squid as a parent for
mine. I would like to force my squid to always query my parent's squid
even if I could reach the site myself.

I have configured:
cache_host test-www-cache.myparent.de parent 3128 3130
inside_firewall my-local-network's.domain.de
and re-started my squid. When I try to retrieve a page from my squid,
I get an error message saying

 "Unable to Retrieve

The system returned:

    No neighbors or parents were queried and the host is beyond your
firewall.

The cache administrator may need to double-check the cache
configuration."

When I remove the inside_firewall setting, my squid does not use the
parent at all (courtesy of my tcpdump and his logs).

What am I doing wrong?

Greetings
Marc

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