[asterisk-users] Why Nat=yes Nat=no Option?

Alex Balashov abalashov at evaristesys.com
Thu Nov 13 09:09:48 CST 2008

Klaus Darilion wrote:

> Actually I would nat=yes always, even if clients are not behind NAT os 
> otherwise the clietn can put some garbage into the contact header (e.g. 
> IP address of an upstream provider) and influence routing.

No.  There is a specific reason RFC 3261 says:

    "Registration creates bindings in a location service for a particular
    domain that associates an address-of-record URI with one or more
    contact addresses.  Thus, when a proxy for that domain receives a
    request whose Request-URI matches the address-of-record, the proxy
    will forward the request to the contact addresses registered to that

This gives the UAC the necessary level of control to determine how it is 
to be contacted.

Imagine, for a example, a scenario in which incoming registrations are 
proxied further upstream for whatever reason - load balancer/distributor 
perhaps? - by an intermediate element.  Do you really want to use that 
proximate hop's received IP address in place of the ultimate sending 
UAC's domain?

-- Alex

Alex Balashov
Evariste Systems
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