I would first regex out then do DNS lookup to a separate field followed by coalesce in case DNS server doesn't know the host name. Here is the SPL with make results: | makeresults
| eval ip_list="https://10.32.52.4,https://10.4.247.4,https://10.76.72.4,https://10.76.73.4,https://10.81.224.10,https://10.81.224.2,http://10.1.1.2,http://10.2.3.4,http://10.4.5.6"
| makemv delim="," ip_list
| mvexpand ip_list
| rex field=ip_list "https?\:\/\/(?<ip>[\d\.]+)$"
| lookup dnslookup clientip AS ip OUTPUT clienthost AS hostname
| eval cmbd_name=coalesce(hostname,ip)
| fields cmbd_name hostname ip
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