[SR-Users] received and rport via parameters

Daniel-Constantin Mierla miconda at gmail.com
Fri Sep 12 09:59:43 CEST 2014


opening this for discussion to get more eyes on the IETF specs to be 
sure I haven't missed any requirements.

We are no adding received parameter to Via header as required by RFC 3261:

18.2.1 Receiving Requests

    When the server transport receives a request over any transport, it
    MUST examine the value of the "sent-by" parameter in the top Via
    header field value.  If the host portion of the "sent-by" parameter
    contains a domain name, or if it contains an IP address that differs
    from the packet source address, the server MUST add a "received"
    parameter to that Via header field value.  This parameter MUST
    contain the source address from which the packet was received.  This
    is to assist the server transport layer in sending the response,
    since it must be sent to the source IP address from which the request

But then RFC3581 says:

4.  Server Behavior

    The server behavior specified here affects the transport processing
    defined in Section 18.2 of SIP [1].

    When a server compliant to this specification (which can be a proxy
    or UAS) receives a request, it examines the topmost Via header field
    value.  If this Via header field value contains an "rport" parameter
    with no value, it MUST set the value of the parameter to the source
    port of the request.  This is analogous to the way in which a server
    will insert the "received" parameter into the topmost Via header
    field value.  In fact, the server MUST insert a "received" parameter
    containing the source IP address that the request came from, even if
    it is identical to the value of the "sent-by" component.  Note that
    this processing takes place independent of the transport protocol.

I understand that if rport parameter is present in incoming Via, 
received has to be added always, even when matching the IP address in 
via. RFC3261 required to be added only when it source IP was different 
than the address in Via.

On the other hand, the RFC3261 says received is needed for helping the 
server to route back the reply, so received shouldn't make much sense 
for upstream. However, apparently, some clients use it (or at least 
check it and don't work properly if not present after a rport -- one 
specific example is that some phone is not making calls after sending 
REGISTER with rport and not receiving received).

RFC3581 says that server behavior affect what was specified in 3261, so 
my plan is to send received always if rport is present, but I wanted to 
see if anyone sees issues with that or there is another more recent rfc 
amending further the behaviour related to rport.


Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Next Kamailio Advanced Trainings 2014 - http://www.asipto.com
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