T-38p losing registration and not re-registering

[AnthonyCNCS]

Hi All,

I wasnt sure where to post this and im slightly sure this is the wrong place but ill ask anyway.

Ive recently started using some T38 from Yealink and they are configured to use a remote hosted (cloud) pbx service. Its all been fine and dandy until recently where some handsets (random) will lose regsitration and will not re-register regardless of what happens. IE reboot the handset, go into the handset web interaface and disable and enable the account. The only solution is the reboot the network f/w // router.

The weirdness appears when the phones were working for months without issue, and since 3 days ago now start this behaviour.

Like i said probably wrong place to ask this question but all help appreciated.

Thanks all in advance!

PS: bonus question -- are there any command line utilities to test SIP connections? for troubleshooting purposes.