On May 9, 2008, at 3:24 AM, Juha Heinanen wrote: > Dean Willis writes: > >> But how does a UA know in advance that a proxy is going to send it? > > it doesn't need to know in advance. > >> And how does the UA know that it is coming from a proxy in response >> to >> its own CRLF stream, and is not an artifact of an echoing NAT or >> other >> weirdness? > > so you assume that nat or some other network box sends back on its > own a > single CRLF when UA sends double CRLF to its proxy and in that > response > all tcp layer stuff would match? in my opinion trying to cope with > that > kind of "weirdness" goes too far. how do you know that your nat box > didn't generate on its own a 200 ok when you sent invite?
Barring very clever timing and counting, it's hard to tell whether a CRLF stream coming back to a a UA is really single CRLFs in response to double CRLFs or is CRLFs being echoed from a broken firewall. And yes, I have seen firewall boxes get confused and echo stuff back. I've also seen TCP stacks get in strange loopback states where the echo is "local" rather than coming from a NAT box. I've never yet seen one get confused enough to send a 200 OK that matches an INVITE, but I suppose somebody could make one that does someday. Never underestimate the power of stupid people in large numbers. -- Dean _______________________________________________ Sip mailing list https://www.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
