[squid-users] Why does Squid need a direct connection?

I've read that Squid shouldn't be behind a firewall because it needs a
direct connection. I'm assuming that this means that the Squid box
must be dangling on the WAN with an Internet accessible IP address.
Can someone explain the issues involved here?

Why does it need a direct connection?
What aspect of Squid doesn't work if it's behind a firewall that does NAT?

Thanks,
~Matt

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