Subject: [SIP] Receiver-tagged Via header

From: Hisham Khartabil <[email-masked]>
Date: Thu, 15 Jun 2000 08:27:43 +0300

Hi all,

The rcf2543bis states in section 6.45.2

"Every host that sends or forwards a SIP request adds a Via field
indicating the
host’s address. However, it is possible that Network Address Translators
(NATs)
change the source address and port of the request (e.g.,from a net-10 to
a
globally routable address), in which case the Via header field cannot be
relied
on to route replies. To prevent this, a proxy SHOULD check the top-most
Via
header field to ensure that it contains the sender’s correct network
address, as
seen from that proxy. If the sender’s address is incorrect, the proxy
MUST add a
“received” parameter to the Via header field inserted by the previous
hop. Such
a modified Via header field is known as a receiver-tagged Via header
field."

So, it is possible that the port is also changed.  Yet the syntax for
via-received looks like this:

via-received = ”received” ”=” host

shouldn't  it be

via-received = ”received” ”=” hostport
or
via-received = ”received” ”=” host [":" port]

Thanks,
Hisham

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