You can use BIG-IP®DNS to configure a return code (RCODE) to return a response to the client when load balancing fails. Only when load balancing fails and the RCODE configuration is enabled, will an RCODE response be returned.
There are two types of load balancing failures where an RCODE response will be returned:
Perform these tasks to configure a return code (RCODE) to return a response to the client.
|NAPTR||The Name Authority Pointer record, NAPTR, aids in the standardization of Uniform Resource Names (URNs). NAPTR records map between sets of URNs, URLs and plain domain names, and suggest to clients the protocols available for communication with the mapped resource.|
|A||The Address record, or A record, lists the IP address for a given host name.|
|SRV||The Service resource record, SRV, is a pointer with which an alias for a given service is redirected to another domain.|
|CNAME||The Canonical Name resource record, CNAME, specifies an alias or nickname for the official, or canonical, host name.|
|AAAA||The IPv6 Address record, or AAAA record, lists the 128-bit IPv6 address for a given host name.|
|MX||The Mail Exchange resource record, MX, defines the mail system(s) for a given domain.|
|NOERROR (No Error)||No error condition.|
|FORMERR (Query Format Error)||The name server was unable to interpret the query.|
|SERVFAIL (Server Failure)||The name server was unable to process this query due to a problem with the name server.|
|NXDOMAIN (Non Existent Domain)||The domain name referenced in the query does not exist.|
|NOTIMP (Not Implemented)||The name server does not support the requested kind of query.|
|REFUSED (Refuse To Answer)||The name server refuses to perform the specified operation for policy reasons.|
You now have an implementation in which DNS has a return code (RCODE) configured to return a response to the client when load balancing fails.