phone disconnect / host unspecified

[rilliam]

I am having an issue with phones that are behind layer2 switches where they appear in asterisk sip status as "unspecified".

Calls placed from the yealink extension will work; however, the pbx thinks the phone is offline and sends incoming calls directly to voicemail.

Is there some setting that will fix this in the phone?

We are using yealink T26P phones with firmware: 7.72.0.30

Thanks!