The script reads stdin and replaces all IP addresses with names before
outputting it again. IPs from private networks are reverse looked  up
via dns. Other IP adresses are searched for in the dnsmasq query log.
This gives names (CNAMEs if I understand DNS correctly) that are closer
to the name the client originally asked for then the names obtained by
reverse lookup. Just run

netstat -n -4 | ./reverse_replace.sh 

to see what it does. It needs 

log-queries
log-facility=/var/log/dnsmasq.log

in the dnsmasq configuration.

The script runs on debian (with ash installed) and on busybox.