On 3/14/16 3:32 PM, Dale R. Worley wrote:
"xaled" <xa...@web.de> writes:
A client originates a session over TCP connection to proxy1 after having it
resolved as top priority outbound proxy from preconfigured edge.test.com
domain. Proxy 1 sends 200 Ok response with following Record-Route header:
Record-Route: <sip:edge.test.com;transport=tcp;lr>
Now client wants to send a reINVITE and instead of reusing the established
TCP connection to proxy1 it resolves edge.test.com over DNS again and this
time receives proxy2 as top priority outbound proxy. Having received proxy2
with highest priority than proxy1 client sends in-dialog request to proxy2
instead of reusing established TCP connection to proxy1.
Now is there any recommendation for the preferential use of established TCP
connection to the proxy1 given that it is resolvable from edge.test.com?
If edge.test.com is resolved using SRV records, RFC 3263 and 2782 do not
allow for prefering to reuse an existing connection -- 2782 prescribes
that potential targets are tried in a particular order based only on the
DNS information.
If edge.test.com is resolved only using A/AAAA records, 3263 does not
prescribe a priority order among the records, so the implementation can
prefer to use the existing connection.
RFC 5923 (Thanks, Brett, for making me aware of this!) is a more
complicated matter. 5923 describes use for TLS only, but its procedures
could be applied to TCP as long as they are only used by the connection
initiator, that only the connection initiator creates an entry in its
alias table.
The larger system-design questions are worth considering. If the DNS
for edge.test.com is adjusted to give higher priority to proxy2, doesn't
that mean that the administrator *really wants* all new requests to go
to proxy2 if possible? That would argue against reusing the TLS
connection simply because its address/port is another target for the DNS
name.
That of course is sub-optimal. Do we really want clients maintaining
many connections to the same target, or making/breaking connections
rapidly? (Especially for TLS.)
If the administrator really wants to move the traffic to a different
server he can always close existing connections.
Thanks,
Paul
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