DNS Does Not Resolve at Some ISP's

1. Confirm record has recently been deleted and re-added
   1. Login at UltraDNS
   2. Click Audit
   3. Under Search Audit Records, search for www.domain.com and click Search
   4. Note time on record with Change Type of Delete
2. Check SOA Min Cache Value
   1. Click Domains
   2. Click domain.com
   3. Click Properties tab
      1. Note value next to Min Cache and confirm that deletion was within the last x seconds. In other words, if the Min Cache is 86400, confirm that the deletion was within the last 86400 seconds

Root Cause

Negative caching at recursive DNS servers due to deletion at authoritative name servers

Steps to Resolution

1. Clear Recursive DNS Cache at Some Providers
2. Wait for negative cache to expire at other recursive DNS providers

Additional Information

Are there options besides waiting?: There is no way for the customer or UltraDNS Support to force the caches of recursive DNS servers (which are operated by other entities, such as IP's) to expire.  Once has recursive server has negative cache for a hostname (the result of an NXDomain received from an authoritative server), it will not check the authoritative for updates until the negative cache clears.

Advice Going Forward: You can reduce the impact of issues like this by making sure that you can modify records instead of adding and deleting them.  When modify is not an option and you must delete a host and re-add it, you can Lower Min Cache Value of Parent SOA prior to the deletion to reduce the downtime.  This has be done prior to the deletion.  It's not effective if done after the deletion.