I use UltraMonkey (www.ultramonkey.org), but it's basically a packaging of Linux-HA and LVS. LVS supports connection persistence, and that works very well. The level of granularity of load balancing is on a per-IP basis, not per-transaction (LVS only does L3 load-balancing, not L4-7). But assuming a reasonable value for the persistence timeout, there should be no problems with SIP transactions (and I haven't experienced anything problematic). Ldirectord also supports SIP health checks (they're pretty basic OPTIONS requests, but it's something), and will fail over to working SIP proxies. Of course, in-progress transactions will fail as the OpenSER process on one box doesn't have the stateful knowledge of the other. Regards, - Brad The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it.