NSX Advanced Load Balancer supports the insertion of the ECS option in a DNS query if the query has no ECS option. It supports updating of the ECS option if the DNS query already has an ECS option.

The DNS has needed improvements since it was first developed. Due to limitations in the size of certain flag fields, return codes, and label types available in the basic DNS protocol, it was decided to expand DNS in a backward-compatible manner to accommodate new flags and response codes, as well as longer responses. Since 1999, extension mechanisms for DNS (EDNS) have been the approach taken to address this challenge.

Figure 1 shows the OPT resource record (OPT RR) is essential for DNS extension. It is structured to permit various options, including the EDNS client subnet option (ECS), which allows authoritative DNS providers to use the extra information to make more informed traffic routing decisions. For example:

  • To provide the geo algorithm with more accurate client location information

  • To provide the consistent-hash algorithm with the client's source-IP address

  • When serving clients coming from a mixture of private and public networks

Figure 1. 1. How the traditional DNS query can be extended

The EDNS option for a DNS profile is supported for IPv6 address too.