[Devel] stateless sip loadbalancer

[Marcus Hunger]

Hi,
following Andreas Granigs proposal 
(http://www.openser.org/pipermail/users/2006-March/003289.html) for creating 
a loadbalanced/redundant sip-proxy-environment, it seems to me, that it is 
not possible to create a scenario with loadbalancers being stateless and 
clients being behind a nat. Establishing an INVITE-dialog went well until the 
callee's 200 OK had to be ACKed. At this point of the session, messages are 
not routed anymore using path's information but only relying on 
record-routing and record-routes lack information about natted clients. So 
the only out of the box solution I am aware of is keeping the loadbalancer 
stateful.

In order to circumvent this problem and enable the lb to be stateless, I 
introduced a record-route uri-parameter which stores the ip-address of the 
client's nat-gateway. These parameters are created by the outgoing lb, are 
kept when the loose-routing sets are created by the uac and the information 
there is then used to route the sip message to the client correctly by the 
lb. The parameter's name is "nat_recv". When it returns in the loose routing, 
it gets translated to "received" so it gets routed correctly. I am doing this 
instead of naming it "received" in first place because "received" would be 
interpreted by the incoming lb immediatly, so that messages would get bounced 
back to the sender in some cases. 

I created a patch for openser 1.1.1 which implements the described 
functionality. It introduces a function for openser.cfg called 
add_rr_received_param, which adds ";nat_recv=sip:[dst_ip:dst_port]" to 
current record-route header field. Also it includes a function which 
translates that nat_recv-parameter to "received", when it occurs in a route 
header field so the packet can then be routed according to the included 
information. The function hooks via register_rrcb.

Please find that patch attached. I would appreciate any comments on that very 
much and would also like to hear about alternative strategies realizing the 
described scenario.

Best regards, Marcus


-- 
Marcus Hunger - hunger at sipgate.de
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