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Hi, Jonathan and all,
From draft-ietf-sipping-nat-scenarios-00, page
47-48:
In the example configuration shown in Figure 22,
the signaling path is established when the SIP UA's register with the
corresponding Proxy/Register (Signaling server). *The SIP REGISTER
message contains an
extension tag carried in the Proxy-Require header, indicating to the Proxy
that the client is behind a NAT* (Note: the client or the Proxy does
not care about the type of NAT, as the same solution applies to all types). This
packet is NAT-ed by the Enterprise NAT with a new
source IP address and port. If the Proxy supports the extension tag, it creates
an association between the IP address and port from which the packet arrived and
the actual address of the user. The response to the Registration message is sent
to this IP address and port (not to the Contact address in the
REGISTER).
My question here is :
Why do we need this extension tag?
--We can know if a UA is behind the NAT by
verifying if the Src IP address ( NATed incase of NAT ) is the same as the IP
address mentioned in the Contact header of the REGISTER message.
Would appreciate if this doubt be
cleared.
Best Regards'
Rahul
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