Kamailio provides an excellent and high-performance vehicle for doing this. It's probably one of its most canonical use-cases. You can do it in one of two ways: 1) Use Kamailio as a redirect server with some state. But this is the more complicated option, and requires that the registering endpoints follow redirects for REGISTER requests, which they don't always. 2) Use REGISTER pass-thru with the SIP Path extension: https://tools.ietf.org/html/rfc3327 Kamailio has a specific module for this: http://kamailio.org/docs/modules/4.4.x/modules/path.html ... and it works great. With a simple config that doesn't have a lot of external I/O dependencies, you can handle tens of thousands of registrations per second, at least. -- Alex Balashov | Principal | Evariste Systems LLC 1447 Peachtree Street NE, Suite 700 Atlanta, GA 30309 United States Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/