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Forums » VOIP etc » Voice Over IP - VOIP » VOIP Tech Chat » How multiple ATAs can be behind same NAT router?
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Links: ·ALL ·Review Your VoIP Provider ·VoIP Providers ·VoIP FAQ ·Porting Rules ·What Codec?
port from AT&T to Vitelity after dryline switch? »
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priller

join:2000-10-20
Gainesville, VA
·voip.ms
·Callcentric
·Vonage
·callwithus

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

said by artisticcheese See Profile :

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.
to forum · permalink · · 2008-01-11 18:10:04 · Reply to this

priller

join:2000-10-20
Gainesville, VA
·voip.ms
·Callcentric
·Vonage
·callwithus

Click for full size
Packet on the inside
Click for full size
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.

to forum · permalink · · 2008-01-11 18:43:32 · Reply to this
Forums » VOIP etc » Voice Over IP - VOIP » VOIP Tech Chatport from AT&T to Vitelity after dryline switch? »
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