Sending dynamic boot filename to clients

[Dave M]

Hello,

I'm currently running version isc-dhcpd-4.4.1 on Ubuntu 20.04. I'm planning
to migrate to Kea but having tried the configuration assistant left me with
more questions than answers to I will need to manually build this config
and it will be a month long project.

I'm trying to set the boot file name for my clients dhcp6 to be dynamically
generated based on the client-id. I have a similar setup working on dhcp4
but can't get it to work on IPv6. These are DOCSIS cable modems trying to
boot and acquire their config.

What I have setup is the following

# declare the option space where the CableLabs options live
option space docsis code width 2 length width 2 hash size 100;
option docsis.tftp-servers code 32 = array of ip6-address;
option docsis.configuration-file code 33 = text;
option docsis.syslog-servers code 34 = array of ip6-address;
option docsis.time-servers code 37 = array of ip6-address;
option docsis.time-offset code 38 = signed integer 32;
option vsio.docsis code 4491 = encapsulate docsis;

subnet6 2001:428:XXXX:1300::/64 {
        range6 2001:428:XXXX:1300::ff01 2001:428:XXXX:1300::ffff;
        set hw_mac_short = concat (
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),0,1))),2),
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),1,1))),2),
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),2,1))),2),
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),3,1))),2),
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),4,1))),2),
              suffix(concat("0", binary-to-ascii (16, 8, "",
substring(suffix(option dhcp6.client-id, 6),5,1))),2)
              );
        set configfile = concat(hw_mac_short, ".cfg");
        log (info, "Sending config...");
        log (info, concat ("Sending config file ", configfile, " to device
", hw_mac_short));
        option dhcp6.domain-search "cm.den.company.com";
        option docsis.time-offset -24200;
        option docsis.configuration-file = concat("cache/ONU-", configfile);
        #option docsis.configuration-file "cache/3basic_OLT.cfg";
        option docsis.tftp-servers 2001:428:XXXX:100:172:19:0:200;
        option docsis.time-servers 2001:428:XXXX:100:172:19:0:200;
        on commit {
                execute("/etc/dhcp/htprov_defaultolt.sh", configfile);
        }
}

I added the log entries to confirm that the data was correctly calculated
and it works:
Oct 30 05:55:01 hus-provserver dhcpd[3162636]: Sending config...
Oct 30 05:55:01 hus-provserver dhcpd[3162636]: Sending config file
f8345a7e48e2.cfg to device f8345a7e48e2

But in the packet trace, the config file field is always missing
Vendor-specific Information
    Option: Vendor-specific Information (17)
    Length: 52
    Enterprise ID: Cable Television Laboratories, Inc. (4491)
    Suboption: TFTP Server Addresses :  (32)
        2001:428:XXXX:100:172:19:0:200
    Suboption: Time Protocol Servers :  (37)
        2001:428:XXXX:100:172:19:0:200
    Suboption: Time Offset =  (38)-24200

When I comment out the dynamic filename and enable the static one
        #option docsis.configuration-file = concat("cache/ONU-",
configfile);
        option docsis.configuration-file "cache/3basic_OLT.cfg";

Then the static name is sent as expected:
Vendor-specific Information
    Option: Vendor-specific Information (17)
    Length: 76
    Enterprise ID: Cable Television Laboratories, Inc. (4491)
    Suboption: TFTP Server Addresses :  (32)
        2001:428:XXXX:100:172:19:0:200
    Suboption: Configuration File Name =  (33)"cache/3basic_OLT.cfg"
    Suboption: Time Protocol Servers :  (37)
        2001:428:XXXX:100:172:19:0:200
    Suboption: Time Offset =  (38)-24200

Would anybody have a possible pointer at what I'm doing wrong?

Thanks

Dave M.
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