Re: How multiple ATAs can be behind same NAT router?

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artisticcheese

join:2004-11-09
Carrollton, TX

reply to priller
Re: How multiple ATAs can be behind same NAT router?

I thought UDP are packets are sent and received on the same port number so on router side it shall be receiving also on 5060?

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· 2008-01-11 18:06:25 ·

priller

join:2000-10-20
Gainesville, VA

·voip.ms

·Callcentric

·Vonage

·callwithus

said by artisticcheese

:

I thought UDP are packets are sent and received on the same port number so on router side it shall be receiving also on 5060?

That's what you see on the "inside" of your network. But, the port is being changed before it leaves the WAN interface.

The combination of the IP address being translated, as well as the port, is what allows you to have multiple ATA's register to the same VoIP provider and not get confused.

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· 2008-01-11 18:10:04 ·

priller

join:2000-10-20
Gainesville, VA

·voip.ms

·Callcentric

·Vonage

·callwithus

Packet on the inside
Packet after PAT

So, to demonstrate this in action. Here is a capture of the same session captured on both the inside interface and the outside interface. Note that port 5060 has been changed to 1061.

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· 2008-01-11 18:43:32 ·


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