[OpenSIPS-Users] Dispatcher Module Question

[Bogdan-Andrei Iancu]

Hello Helmut,

Please see the inline comments.

Regards,
Bogdan

Helmut Kuper wrote:
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> Hello,
>
>
> I'm loocking for a HA solution for 2 node opensips proxy setup. I found
> opensips' dispatcher module, but I'm not sure if it is able to handle
> serverral pairs of SIP-proxies e.g. 1 Dispatcher pair in front of n
> sip-proxy pairs (where n > 1).
>
> I think it can, but I would like to get an ok from you :)
>   
[bogdan]
yes, you can, but as you already figured out, you have to pay a lot of 
attention to NATed clients - when dealing with a NATed client, you have 
to communicate with it all the time from the same IP and port (to be 
sure that the traffic goes through the NAT). So, in your case, all the 
traffic will have to go via the dispatched machine.
>
> Further, if it can do the job, I expect a problem with firwall in front
> of the Dispatcher Pair in case of no recordroute in the Dispatcher as
> follows
>   
[bogdan]
based on the above conclusion (that SIP traffic must go via 
dispatcher),  you need to implement a mechanism to ensure this. The 
simplest is RR (but you have the extra hdr); also you can try to 
implement a static routing logic between proxy and dispatcher (D sends 
all traffic received from outside to P; P sends all outgoing traffic to D).
> A SIP-Request comes in through FW to Dispatcher (Dispatcher is the
> SIP-Proxy from UserAgent's point of view). Dispatcher routes it to
> SIP-Proxy-Node0. SIP-Proxy-Node0 sends replies back to UserAgent passes
> by the Dispatcher (because of no recordroute).
>   
[bogdan]
This is not correct - the replies are routed back exactly on the same 
path as the request - this is SIP :). So, you do not have to worry about 
the replies.

But what you are saying is true when comes to sequential requests - like 
BYE - BYE must follow the same path (based on RR) as INVITE in order to 
go through FW/NAT.
> So from FW's point of view an IP-packet was sent to destination address
> A (here Dispatcher), but IP-Address B (here SIP-Proxy-Node0) sends an
> answere.
>
> Do I understand the dispatcher functionality right? Has anyone a similar
> setup and some experiences with it in terms of whether it is knocking
> out firewalls or not? Or do I have to enable recordroute in Dispatcher?
>   
[bogdan]
For the beginning I strongly suggest using RR on dispatcher machine - 
later, when you understand the routing logic better, you can use a 
static logic to route through the dispatcher (it is a bit more difficult 
to integrate, but it is more efficient).
> For UserAgents view I think they prefer to communicate with only one
> IP-Address (due to security reasons) instead of communicating with a
> growing number of different SIP-Proxy-Nodes resp. IP-Networks.
>   
[bogdan]
That is true.
> regards
> Helmut
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