UC500.com Cisco CallManager Express, UC500 reference

In working with the UC520 and using the configuration tool, I think I found a bug. I set up an Internet based SIP provider and the default firewall configuration on the UC 520 worked fine for incoming calls to phones but calls to the Auto Attendant failed. Calls transferred to Voicemail failed as well. To fix this I had to do two things.

Allow SIP to SIP hairpins

Type in

Config T
voice service voip
allow sip to sip

Allow SIP through the firewall to the Unity Express Module

If you are using the default firewall configuration you may need to allow calls that now seem to be originating from the outside interface to be allowed through the access list on the service engine interface.

to accomplish this I did the following:

Turned on inspection for inbound SIP requests to allow media channels to come through the firewall.

Config T
ip inspect name voip sip
interface Integrated-Service-Engine0/0
ip inspect voip in

Next I had to modify the acess list on the service engine interface to allow inbound SIP.

I added a line that looked like.  access-list 102 permit udp any any eq 5060

(I actually copied the associated access-list, changed it in notepad and put it in with a new access list number. I then used the command access-group NEWlist# in to assoiate it with the interface.

Now, This might be just because I set up a DMZ as well on my firewall during install, I'm not sure. 

As always back up your configuration before you modify it.