Mr Dash Four wrote:
>  > Alternatively, it's more admin but also more reliable to statically
>>  configure everything. Manually configure each SIP device to use a
>>  different port for it's SIP traffic, and a different port range for
>>  it's RTP traffic. Configure them with knowledge of their public IP,
>>  and manually configure your firewall with all the corresponding NAT
>>  mappings.
>>  
>THAT is exactly what I have been doing for the past year or so - very
>painful experience, though once done it works for good (well, most of
>the time!). I am also strongly against using STUN as, for me, this is an
>abomination and should never EVER be used.

I agree, STUN is an abomination. However, as long as we have NAT 
(also an affront to common sense) then we need tools to work around 
the breakage. My experience is that, given a well behaved gateway, 
STUN is actually highly effective.
Where it breaks down is gateways that are designed by people with the 
strange idea that randomising ports is a good idea. When that 
happens, the device cannot determine it's outside port since it will 
change between doing STUN and doing VOIP. For that reason I always 
advise strongly against having anything to do with Zyxel in your 
network if you also want to do VOIP.

Commercial VOIP providers (we use Gradwell at work) get round these 
problems by providing NAT proxies that ignore the address/port 
combinations in the SIP packets and instead look at the actual 
address/port the SIP and RTP packets come from.

I think you can probably tell what's been driving me nuts for the 
last few years ! When I started 5 years ago, they were just 
experimenting with VOIP at work - and all the phones were on public 
IPs outside the firewall because they hadn't (at the time) figured 
out how to make them work otherwise. Fortunately we had the IPs 
available because of our hosting services.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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