Refreshing Cached DNS entries

Hi, I recently received the email below. I know that we are using an Asterisk PBX, however I am not sure how to check if it caches DNS records and how I can refresh the cache. If somebody could help me figure out what I have to do to resolve this, I’d greatly appreciate it.

I also would like help determining the lenght of my EXPIRES headers.



SIPSTATION will be undergoing maintenance on the morning of July 20th. The purpose of the maintenance is to replace the existing infrastructure with a newer platform.
What this means for you
The DNS records for the current trunking proxies are changing. If you are using a PBX which caches DNS records (such as Asterisk) you will need to ensure that your PBX has refreshed it’s cached DNS entries sometime after July 20th and before July 31st.
The DNS records will change on July 20th, but the proxies that are currently referenced by the DNS records will continue to work through July 31st. As long as your PBX has picked up the DNS changes before the 31st there should be no service interruption.
Also, as part of our migration, we will soon be enforcing that Expires headers in REGISTER requests are not to be set below 1800 seconds. For customers with Expires headers below 1800, they will need to modify their system accordingly to use a greater expiration.
Thank you for your time and understanding!

Unless you’ve modified your installation to install a caching DNS server, I doubt you’ll have a significant problem. The installation of a caching DNS server was a common solution to an Asterisk bug that caused Asterisk to hang when you lost internet service. It is unnecessary with Asterisk 1.8, as that bug is gone.