All, wondering myself where I can find an RFC section stating how an UAC shall behave, if it discovers itself being behing a symmetric NAT (as of RFC3489). Shall it fill Via, Contact and SDP with it's internal IP:Port, or shall it use it's reflective ip:port pair, even if knowing that it will not be useful for anything (apart from "hiding" internal IPs)?
I would opt for the former, as this would allow NAT-aware proxies (or those braindead devices calling themselves ALG) to easily help him. In the latter case a proxy would still be able to discover that the UAC needs "some assistance" by comparing source ip:port with what is written in it's Via/Contact headers, but this alone would usually not help against location databases filling up with registrations using many different Contact's. Unfortunately out in the wild I've met both behaviours. I would really like to try explaining some vendor what they are doing wrong - however I did not find anything "proving" what the correct behaviour would be in this case. Can anyone give me a little hint? Best regards, Thomas Gelf -- mail: [email protected] web: http://thomas.gelf.net/
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