[reSIProcate] Multiple Addresses on the same interface

[Gabriel Hege]

Hi!

I have a problem using the resiprocate stack on a (Windows) machine with 
multiple IP addresses assigned to the same interface.

The setup is the following:
To be able to run multiple services on the same port on a single 
machine, it has multiple IPs from the same subnet assigned to its 
network interface. When I tell the stack to not bind to the primary 
address but to any other address of this interface, it can't send any 
locally initiated transactions, but fails with the following message:
SIP/2.0 503 No matching transport found

Replying to incoming messages works properly.

I think the problem lies in how the outgoing transport is chosen:
WinCompat::determineSourceInterfaceWithoutIPv6() only returns the first 
matching entry from GetIpAddrTable(), but in my case for example the 
second would actually be the right one. So I see two solutions to this 
problem:
1. Either checking if we have got a transport for the chosen address in 
determineSourceInterfaceWithoutIPv6() and else trying the next one.

2. Or having determineSourceInterfaceWithoutIPv6() return a list of 
matching addresses and calling findTransportBySource() on all of them in 
TransportSelector::transmit() until we find a matching one.


Are there any better solutions to this problem?

I get the same error, when compiling with NO_IPHLPAPI. I haven't looked 
into this code yet, but I guess the problem is pretty much the same and 
might also apply on Unix/Linux.



By the way, why is there all this windows-specific code for iphlpapi.dll 
when doing it the standard way works as well? Especially seeing the 
following comment in front of determineSourceInterfaceWithoutIPv6():

// !slg! - This function is horribly slow (upto 200ms) and can cause 
serious performance issues for servers.
//         We should consider finding more efficient APIs, or caching 
some of the results.



best regards,
  gabriel