Underscores and Latin2 characters in ISC DHCP + BIND9 DDNS hostnames

[Mirsad Todorovac]

Dear All,

1. I was receiving errors for a long time like this one:

May 20 11:50:42 domac dhcpd[29435]: DHCPREQUEST for 192.168.100.59 from 
a8:7d:12:f8:e8:6c (HUAWEI_Y7_Prime_2018-d716) via eth0
May 20 11:50:42 domac dhcpd[29435]: DHCPACK on 192.168.100.59 to 
a8:7d:12:f8:e8:6c (HUAWEI_Y7_Prime_2018-d716) via eth0
May 20 11:50:42 domac dhcpd[29435]: Unable to add forward map from 
HUAWEI_Y7_Prime_2018-d716.local.alu.hr to 192.168.100.59: REFUSED

May 20 11:48:47 domac named[5524]: zone local.alu.hr/IN: 
Win-Ra\159unalo.local.alu.hr/A: bad owner name (check-names)
May 20 11:48:47 domac dhcpd[29435]: Unable to add forward map from 
Win-Ra�unalo.local.alu.hr to 192.168.100.235: REFUSED

Additionally, some users have added ČĆĐŠŽčćđšž Latin2 characters to 
hostnames or smartphone names on WLAN.

It is difficult to change all of these, especially on user's smartphones 
who usually connect without even seeing us administrators.
Also, disabling BIND9 name checks might make users unable to browse as 
some other services would reject their reverse DNS names as spoofed.

It would be very useful if there was a way to do in DHCPD dhcp-eval 
scripting what is done with the effect of:

% tr '_ČĆĐŽŠčćđšž' '-CCDSZccdsz' < in > out

that is, transliterate characters, or search & replace. I couldn't find 
that option in dhcpd.conf nor in dhcp-eval.

2. I have also tried this to have PCs 12h lease time and smartphones 30min,
but it did not work:

if substring (option host-name, 0, 3) = "PC-" or
    substring (option host-name, 0, 8) = "DESKTOP-" or
    substring (option host-name, 0, 4) = "ALU-" or
    substring (option host-name, 0, 2) = "S-" or
    substring (option host-name, 0, 3) = "NO-" or
    substring (option host-name, 0, 6) = "OKIRU-" or
    substring (option host-name, 0, 7) = "OZAFIN-" or
    substring (option host-name, 0, 8) = "MikroTik"
{
         default-lease-time 43200;
} else {
         default-lease-time 1800;
}

Thank you very much.

My version of DHCPD is:

root at domac:~# dpkg -l isc-dhcp-server
ii  isc-dhcp-server 4.4.1-2+deb10u1 amd64        ISC DHCP server for 
automatic IP address assignment
root at domac:~#

Best regards,
Mirsad Todorovac

-- 
Mirsad Goran Todorovac
CARNet sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
-- 
CARNet system engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
tel. +385 (0)1 3711 451
mob. +385 91 57 88 355