SIP packets not exiting router

[MarkiP]

Hi,

We are having an issue with some VoIP phones in one of our offices, they periodically fail to register, we can still ping them internally but cannot make calls etc. Forcing them onto a new IP reservation then rebooting fixes this. We have run DHCP from the router, server & set them IP's statically but seemingly makes no difference.

On running a few packet captures from the MX84 on the LAN interface, I can see traffic between one of the non-functional phones and the external IP of the VoIP provider, including some outgoing only SIP packets-no responses coming back in. However, on the WAN side capture I cannot see these outgoing SIP packets (nor any incoming) for that internal IP address.

On assigning a new IP and rebooting the phone and repeating the captures, SIP packets for that phone are showing on both the WAN and LAN interfaces as expected and the phone works.

The phone provider suspects a NAT issue, we have no 1:1 or 1:Many NAT mappings set up. It seems as if the outgoing SIP packets are reaching the router and not being forwarded out over the internet, however the phone can successfully make TCP connections. Also this issue is only periodic, and affects all phones which have to be manually assigned a new IP to get them working again.

Leaving me a bit baffled as to what is causing this and why the SIP packets are not exiting the router (or at least why I cannot see them). Any help would be much appreciated on this.

Many thanks,

Mark

[Seshu]

Hello @MarkiP,

From your description, it is possible that the MX is dropping the packets before forwarding on the WAN. Our support team needs to take a look at the live flows and logs from the MX when the issue is happening. I would suggest opening a support case to work on this.

My initial thoughts indicate this could be due to out-of-order packets being sent on the MX LAN and causing the packets to be dropped. Let me know the MX firmware on which you saw this issue.

Let me know if you have any questions.

Regards,

Meraki Team 

[MarkiP]

Thanks for the response, the MX84 is currently on 14.40, up to date stable release.

I shall look into raising a support case.

[Seshu]

The out-of-order packets are dropped in any firmware 14.36 or later. That specific bug is fixed in 15.23 beta firmware. But, our support team can check the logs and confirm whether you are hitting this issue or not.

Regards,

Meraki Team

[PhilipDAth]

Is their anything in the Security Centre under "event log"?  There is a slim chance IPS is triggeering on something.

You could laso try turning off AMP and IPS for 24 hours and see if the behaviour is changed in anyway.

On a seperate note, we have found the most reliable method when using SIP phones is to use SIP/TLS for thetransport, and then (second option) TCP.  TCP takes care of so many problems.

We never use UDP anymore.  It is too problematic.

What are you using for SIP registration?

[MarkiP]

Hi Philip,

I did take a look at the event logs and there was nothing relevant unfortunately. It appears to be sending the SIP packets over UDP.

Thanks for the suggestions-I'll look into them and get onto the support team as well.

Much appreciated.

[SoCalRacer]

Might take a packet capture focusing on the host device to see whats going on during registration, could be a bunch of possibilities.