AW: DDNS updates

John Hascall john at
Wed Aug 2 12:20:47 UTC 2006

> An immidiate switch to a ISC DHCP-only network will not be possible. 
> This means, there are instances (clients, MS DHCP server) which will
> update the domain. 
> When traveling to a location with an ISC DHCP server, I would like to
> only have the ISC do the updates. This does not work, because it does
> not touch the record, in regards of the missing TXT record.
> So I would like to FORCE the ISC DHCP server doing the update although
> the TXT record is missing.

You could surely do this by a different modification to
the ddns_update_a function in the common/dns.c file.
It you omitted this whole chunk:

         * DHCID RR exists, and matches client identity.
        updrec = minires_mkupdrec (S_PREREQ,
                                   (const char *)ddns_fwd_name -> data,
                                   C_IN, T_DHCID, 0);
        if (!updrec) {
                result = ISC_R_NOMEMORY;
                goto error;

        updrec -> r_data = ddns_dhcid -> data;
        updrec -> r_size = ddns_dhcid -> len;
        updrec -> r_opcode = YXRRSET;

        ISC_LIST_APPEND (updqueue, updrec, r_link);

that would remove the test for the TXT record entirely.

**** But unless you run a *very* tight organization indeed       ****
**** this would be a tremendous risk of accidental or purposeful ****
**** mayhem.  Suppose a client suggested to DHCP that its name   ****
**** was something like <name-of-your-domain-controller> and     ****
**** DHCP updates your DNS ...                                   ****

If you segregated your clients all into specific subdomain(s)
that contained no servers and you setup DNS to only allow those
subdomains to be dynamically updated by DHCP/clients then at
least they could only stomp on other clients.


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