diag_arp does not display reverse resolved hostnames containing underscore
is_hostname() and is_domain() allow underscore in the names. So it is possible to have underscore in host names, for example in DHCP server static mapped entries I have some things like:
These reverse-resolve fine - 10.42.3.4 becomes client-pc-01_LAN
But the preg_match in diag_arp.php misses such names that have an underscore in them.
I noticed this when looking into forum post: https://forum.pfsense.org/index.php?topic=88956.0
Pull request: https://github.com/pfsense/pfsense/pull/1497