DNSE-793 — Querying to name loops back to itself
Proxy is to generate a new internal request (CNAME or CACHE one - see dns-proxy(8) manual page), but the same request from the same originator is already pending. It means that CNAME or NS records chain loops back to itself.
Request is replied with ServFail response code.
In case of CACHE request, this can be caused by expiring of some items from cache. In this case, next request will resolve the domain anew, from the parent server.