[SR-Users] Reuse TLS connections

[Klaus Darilion]

On 13.02.2012 18:07, Bruno Bresciani wrote:
> Hi all,
>
> There is the possibility to kamailio reuse the TLS connection created by
> other SIP server?  When kamailio use t_relay function to send a SIP
> request message to other server, kamailio verify if already exist some
> connection established with the destiny and use it even if this
> connection was created by the other SIP server.
>
> In short, I want to keep only one connection between kamailio and SIP
> server. Sometimes kamailio will be a client and others a server.

This is quite difficult. For example, on a server with a single IP 
address may run several SIP proxy instances with different purposes. 
Each of these proxies uses another listening port, e.g: 1.1.1.1:5061, 
1.1.1.1:6061, 1.1.1.1:7061.

If on of these proxies establish a TCP connection to another proxy, e.g. 
2.2.2.2:5061, it uses an ephemeral source-port. Thus, for the TLS-server 
(the receiver of the TLS connection) there is no way to know which of 
these SIP proxies on 1.1.1.1 established the connection. There are lots 
more issues e.g. with certificate validation - a proxy may use various 
certificates for several domains. Maybe you can overcome these problems 
if all the proxies are controlled by you, but in an open environment 
this kind of connection reuse does not work.

Thus: connection reuse can only be used for transactions in the same 
direction with the same target domain. For example if you have a proxy 
at 1.1.1.1:5061 authoritative for a.example.com and b.example.com and 
you have a proxy at 2.2.2.2:5061 authoritative for y.example.com and 
z.example.com then you will end up with 4 TLS connections:

1. 1.1.1.1 as TLS client to a.example.com
2. 1.1.1.1 as TLS client to b.example.com
3. 2.2.2.2 as TLS client to y.example.com
4. 2.2.2.2 as TLS client to z.example.com

Unless you have s strange setup with strange requirements I do not see 
any benefit in forcing all messages into a single TLS connection.

regards
Klaus