I use Asterisk talking SIP to a Cisco GW. I have made it work with Asterisk registering to the registrar function on IOS GW, but this is problematic if you have multiple users behind the Asterisk server and want to pass on the correct ANI.
It works most simply with no registration, just treating it as a sip peer:
mysql> select name,type,ipaddr,host from asterisk.sip_peers;
+---------------------------+--------+-----------------+-----------------+
| name | type | ipaddr | host |
+---------------------------+--------+-----------------+-----------------+
| sj-pbx-gw1 | peer | 192.168.238.196 | 192.168.238.196 |
+---------------------------+--------+-----------------+-----------------+
I think I had problems when I first set only the ipaddr statically, and it started working after I also set the host field to the ip addr. Don’t remember clearly though.
Of course you have to have your dialplan set up correctly on Asterisk side and all your dial peers set correctly on the IOS GW, which will take more than a quick forum response except for simplest casest.