 messages: R1-PBX(config-sip-ua)#registrar gad Malformed SIP Registrar address. Valid formats are: ^(dns:.*) ipv4:[0-9]?[o-9]?[o-9]?\.[o-9]?[o-9]?[o-9]?\.[o-9]?[0-9] Not SO scary if you're used to regular expressions, but a tad overwhelming if you're not. If you're using DNS names in your config, you'll need to at least configure your router to know where to get DNS resolved: R1-PBX(config)#ip name-server 192.168.1.200 R1-PBX(config)#ip name-server 192.168.1.205 If, like me, you've disabled DNS lookups on all your routers SO you don't have to watch your typing mistakes try to resolve in DNS, you're going to need to turn that function- ality back on for DNS to work: R1-PBX(config)#ip domain-lookup The following command puts the name from the registrar command into SIP diversion headers used in call forwarding. Normally, CME will use the domain from the router itself: R1-PBX(config-sip-ua)# host-registrar Next, we'll configure the authentication outbound: R1-PBX(config-sip-ua)# authentication username 608222222 password 123456789 Notice that I'm not referencing my telephone numbers anywhere. That threw me when I first started with SIP on CME. That may be different with different providers, too. For example, providers may use your as- signed telephone number as your username. Next, we'll configure the credentials to allow our CME to register with our provider: R1-PBX(config-sip-ua)# credentials username 608222222 password 123456789 realm voip.sip-provider.com Here's where things get complicated. I have two SIP trunks, and I'll need to register them both if I want people to be able to call into both numbers. Here's what happens when I register the second trunk: R1-PBX(config-sip-ua)#$ credentials username 557333333 password 123456789 realm voip.sip-provider.com No errors whatsoever! Small-Office VolP Example Here's the rub. It only works great with multiple trunks like this on IOS 15.0(1)XA5 or later, which means I'm on CME 8.0. During my testing, I had to upgrade my router four times to get certain features pertaini