[sr-dev] Problems with mhomed

Marius Zbihlei Marius.Zbihlei at 1and1.ro
Fri Nov 27 11:40:53 CET 2009

As I see in sip-router and in kamailio, the mhomed implementation is very very slow . For each SIP packet a
temporary socket is created, connected to the remote host and than checked to see what interface was selected
to connect the socket(see method get_out_socket() in forward.c)

As test have shown, this implementation, albeit correct from a funtional point of view, it's really too slow 
(or too expensive) to be used in medium-large production setups.

I am currently working on a patch that mitigates this problem. The way the patch works is like this:

1. Get the routing table from the kernel via NETLINK sockets(done at start)
2. Construct a link list of routes, each entry for one interface(either real of virtual). The structure will hold
the address of the interface and the destination (as reported by route -n)(this will be a CIDR entry). Also it's 
decided if on that interface a default route has been assigned(done at start)
3. get_out_socket() will be changed to loop thru the list described above and decide based on the destination member
of the struct describe above on what interface the packet is to be routed. If no destination is matched than the 
default one is selected.(done for each packet)
4.A NETLINK socket will be added to the poll()ing loop so it can monitor the changes in the kernel's routing table
and update the internal structure if necessary.(done at start)(The table is updated only if administration changes the
routing table via route or ip route commands)

I have implemented the first 3 steps and preliminary tests look ok. step for is required only if we want updates on
the routing table in real time.

1. This only works for Linux, AF_INET sockets. AF_INET6 is also supported but i don't know to what extent
2. For BSD, route sockets should replace the NETLINK sockets

What are your suggestion about this? Should this patch (when completely finished) be commited?

Thanks for any suggestions!



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