07-31-2013, 01:21 AM
Yealink phones have a firmware bug. We have tested this on the model T28P phone, but believe it to occur in all yealink models.
When the phone does a DNS lookup it is ignoring the published "time to live" value. When the DNS lookup expires, the phone is supposed to do another DNS lookup. Instead, the phone caches the value of the domain name, and continue to use the name past its expiration.
Further, if a phone tries to register to a domain, and no answer is received, it should do another DNS lookup immediately.
Please find that attached file, which shows that after 2 minutes of TTL, the phone did not send another DNS request.
When the phone does a DNS lookup it is ignoring the published "time to live" value. When the DNS lookup expires, the phone is supposed to do another DNS lookup. Instead, the phone caches the value of the domain name, and continue to use the name past its expiration.
Further, if a phone tries to register to a domain, and no answer is received, it should do another DNS lookup immediately.
Please find that attached file, which shows that after 2 minutes of TTL, the phone did not send another DNS request.