Inbound and Outbound Intermittently Stop Working

[jcalvin]

Cheers everyone,

I'm running into an issue where inbound and outbound will randomly stop working for everyone.

We use Cisco WebEx which connects to a local cube router (isr4321). We were using T1 until a few days ago and switched over to an ITSP for SIP (which is around the time the issues started). The ITSP isn't seeing anything wrong on their end and thinks it's an issue with our Cube. 

Here are the symptoms I've observed when the calls stop working:

- On the webex side when attempting to make an outbound call I get the error "The number cannot be reached at this time, please try your call again later".

- When someone makes an inbound call it rings once and then hangs up. However, after the call disconnects webex is still showing the call is ringing.

I've attached a copy of the running config and the output for debug voice ccapi inout and debug ccsip messages 

Thanks in advance for any assistance!

[TechLvr]

@jcalvin I noticed your CUBE IOS version is 17.3.4a. This version is full of defects that especially affect SIP calls. 
I suggest you upgrade to 17.6.4 which is a stable version and has many of the previous bugs fixed.

The upgrade should take care of the existing issues, but if they are not gone entirely, then look at the following potential problems.

Your CUBE sends its private IP address in the SDP headers towards Webex. Does your NAT firewall do SIP ALG to update the SDP headers with a Public IP address? SIP ALG does not work very well on some firewalls? Use sip profiles in the CUBE to update the SDP headers and disable ALG on the firewall. 

Your CUBE sends the 180 Ringing w/ Require: Rel100 towards the ITSP but the ITSP does not send a PRACK. While this may not be a big issue but I would use SIP Profiles to remove the "Require: 100Rel" from 180 Ringing. 

[jcalvin]

Thanks for the info about the IOS version, I'll get that upgraded tonight.

We use a Meraki MX which does not support ALG. Should I try port forwarding?

[TechLvr]

After you uprage to 17.6.4, test your calls again and share some logs similar to how you did in your original post.

I can review the logs and provide suggested changes to your sip-profiles 200 based on what the SDP headers look like.

As for the firewall, I don't think you don't need to apply any changes yet. The SIP traffic is certainly allowed/routed correctly or else you the CUBE would not have been able to communicate with the WebEx cloud. I assume the RTP traffic would already be allowed as well since this is not a new setup.  

[jcalvin · Accepted solution]

I upgraded the IOS version, but the issue was still happening.

I did some more troubleshooting with the ITSP, and we found that the Cube router and ITSP would lose network connectivity with each other. I couldn't figure out what was causing the network issue, so I put the routers on a stand-alone network with their own MX appliance, and so far, there haven't been any issues.

Thanks for taking the time to look into this issue and offer advice and feedback - it's very much appreciated!