Using Client Subnet in DNS Requests
BIG-IP DNS 14.0 now supports edns-client-subnet (ECS) for both responding to client requests (GSLB) or forwarding client requests (screening). The following is a quick start on using this feature.
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Published Sep 14, 2018
Version 1.0
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In version 13.1.1 you would have to consider an iRule to emulate the behavior that is described in this article. My previous article covers this here: Implementing Client Subnet in DNS Requests.