asterisk users - Sep 2004 - Calling to Broadvoice via Linux MASQ (NAT)

I just signed up for Broadvoice, and used a similar network configuration that 
I have on stanaphone, voipjet, and others.

My asterisk box is behind a vanilla Linux masquerade (netfilter/ipchains) 
firewall.  The SIP and IAX services have been working fine in both directions 
for the other SIP termination services.

The Broadvoice inbound service worked immediately. (which to me is odd, inbound 
is usually relatively problematic over NAT)

But I cannot place calls, due to a NAT problem.  Often I get a fractional ring 
at the destination,  and get the familiar "Maximum retries
exceeded..." before
the call drops.

When I place my Asterisk box on a genuine internet IP number, everything is 
perfect.  But I really don't want to do that.   What's weird is that the
other
SIP providers work just fine in my setup.

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On a sort-of related topic, does Broadvoice have any plans to support IAX?
I never have any grief with IAX via NAT.
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Any help in this regard would be -greatly- appreciated!

Jerry Black
Seattle, Washington