I am very new to asterisk and SIP so these questions may be fairly basic. I have setup an asterisk system based on Red Hat 8.0 Linux with a few analog cards from Digium (X101P's). I have also purchased a SNOM 200 phone and a couple of soft SIP clients for windows. Everything (so far) is working nicely. As I understand it, the asterisk server performs as a SIP proxy. The sip.conf file sets up the SIP user agents (clients) connections -- whether they are dynamically addressed, are they "friendly", etc. The name given in the [context] is what is used by the extensions.conf file to associate an extension with this user agent. Example: ; ; SIP Configuration for Asterisk ; [general] port = 5060 ; Port to bind to bindaddr = 172.16.1.155 ; Address to bind to context = default ; Default for incoming calls ; [ext1111] type=friend secret=1234 host=dynamic defaultip=172.16.14.1 ; ; excerpt from extensions.conf for Asterisk ; exten => 1111,1,Dial,SIP/ext1111|20 exten => 1111,2,Voicemail,u1111 exten => 1111,102,Voicemail,b1111 Now based on my ability to configure the user agent(s), which is sometimes difficult because it seems every user agent vendor seems to have a slightly different SIP vocabulary and sparse documentation, I point my SIP clients at asterisk, dial the extension, and it works. Here are my questions: 1) What purpose does the "defaultip" entry in the sip.conf file serve if it is set to host=dynamic? 2) If my asterisk server has just one IP address, can I use bindaddr 0.0.0.0 instead of specifically setting the IP address? 3) I assume the use of username and password in the sip.conf is strictly for the ability to authenticate a user agent to the asterisk server -- so some yahoo just doesn't stick any old user agent on your network? 4) The BIG question: it is my understanding of SIP that the really cool feature (of SIP) is the ability to register a user such as (sip:swoolley@adstelecom) at the user agent level and some type of registration service would associate sip:swoolley@adstelecom with the user agent (example: 1111@172.16.14.1). All the SIP clients I have dealt with have a line for "register as" with username and password. Can asterisk as a registration server? I noticed "sip show registrations" command inside asterisk, but no entries ever show up? If asterisk can act as a registration server, how is the feature/service started and configured? Thanks for some insight. Steve Woolley swoolley@adstelecom.com