Howto:VOIP through NAT routers: Difference between revisions
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If a private signaling endpoint hands-out a private IP address (signaling or media) the external endpoint won't be able to reach that IP address. | If a private signaling endpoint hands-out a private IP address (signaling or media) the external endpoint won't be able to reach that IP address. | ||
== What | == What will work == | ||
The only leliable way to get the hole thing working is to handle the problem on the private network.<br> | The only leliable way to get the hole thing working is to handle the problem on the private network.<br> | ||
Keep your private signaling endpoint from hand-out private IP addresses. | Keep your private signaling endpoint from hand-out private IP addresses. | ||
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Configure the public STUN server on your private signaling endpoint. It will use STUN to create a NAT mapping on the fullcone NAT router. It will then hand-out the mapped IP addresses (signaling and media) instead of the private ones. | Configure the public STUN server on your private signaling endpoint. It will use STUN to create a NAT mapping on the fullcone NAT router. It will then hand-out the mapped IP addresses (signaling and media) instead of the private ones. | ||
== What | == What may work == | ||
It MAY work even if the private signaling endpoint does not care about giving private IP addresses to the external endpoint, | It MAY work even if the private signaling endpoint does not care about giving private IP addresses to the external endpoint, | ||
but only if the external endpoint has implemented a special workaround for NAT-unaware devices. | but only if the external endpoint has implemented a special workaround for NAT-unaware devices. | ||
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All innovaphone devices work symmetrically (signaling and media). | All innovaphone devices work symmetrically (signaling and media). | ||
== What | == What won't work == | ||
'''Outgoing T.38 fax through symmetric NAT routers WILL NOT work''', | '''Outgoing T.38 fax through symmetric NAT routers WILL NOT work''', | ||
since the external called party is responsible to start communication with the fax answer tone indication. | since the external called party is responsible to start communication with the fax answer tone indication. |
Revision as of 13:50, 27 September 2007
Abstract
This page discusses NAT traversal of VOIP.
Introduction
VOIP signaling involves the exchange of IP addresses. Signaling addresses and media addresses RTP or T.38).
If the signaling crosses network borders you may get in trouble with private IP addresses. If a private signaling endpoint hands-out a private IP address (signaling or media) the external endpoint won't be able to reach that IP address.
What will work
The only leliable way to get the hole thing working is to handle the problem on the private network.
Keep your private signaling endpoint from hand-out private IP addresses.
What you need
You need a fullcone NAT router and a STUN server in the public network.
How to configure
Configure the public STUN server on your private signaling endpoint. It will use STUN to create a NAT mapping on the fullcone NAT router. It will then hand-out the mapped IP addresses (signaling and media) instead of the private ones.
What may work
It MAY work even if the private signaling endpoint does not care about giving private IP addresses to the external endpoint, but only if the external endpoint has implemented a special workaround for NAT-unaware devices.
What you need
You need a NAT router that at least do symmetric NAT.
How to configure
Nothing to do on the private equipment. The private signaling endpoint will hand-out private IP addresses.
The external endpoint will detect and ignore all private IP addresses/ports and will reply to that IP address/port where it receives from (signaling and media).
It won't work if the internal endpoint does not work symmetrically (signaling and media)!
All innovaphone devices work symmetrically (signaling and media).
What won't work
Outgoing T.38 fax through symmetric NAT routers WILL NOT work, since the external called party is responsible to start communication with the fax answer tone indication. On the other hand the external endpoint must wait for the internal endpoint to send a T.38 packet in order to know where to send the fax answer tone indication.