DNSSEC Part II: the Implementation

Reconfigure Zone's BIND Config

Now that you have a new .signed zone file, you will need to update your zone's config in BIND so that it uses it instead of the plain-text file, which is pretty straightforward:

zone "greenfly.org" {
  type master;
  file "/etc/bind/db.greenfly.org.signed";
  allow-transfer { slaves; };

Enable DNSSEC Support in BIND

Next, update the options that are enabled in your main BIND configuration file (often found in named.conf or named.conf.options), so that DNSSEC is enabled, the server attempts to validate DNSSEC for any recursive queries and DLV (DNSSEC Lookaside Validation) is supported:

options {
  dnssec-enable yes;
  dnssec-validation yes;
  dnssec-lookaside auto;

When you set dnssec-lookaside to auto, BIND automatically will trust the DLV signature it has for dlv.isc.org as it's included with the BIND software. Alternatively, you can add a DLV key manually if you add an additional BIND option and trusted key:

options { dnssec-lookaside . trust-anchor dlv.isc.org.; };
trusted-keys {
        dlv.isc.org. 257 3 5
QKtUdvNXDrYJDSHZws3xiRXF1Rf+al9UmZfSav/4NWLKjHzpT59k/VSt TDN0YUuWrBNh";

Once you are done changing your BIND configuration files, reload or restart BIND, and your zone should be ready to reply to DNSSEC queries.


To test DNSSEC support for a zone, just add the +dnssec argument to dig. Here's an example query against www.greenfly.org:

$ dig +dnssec www.greenfly.org

; <<>> DiG 9.8.1-P1 <<>> +dnssec www.greenfly.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13093
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 3, ADDITIONAL: 5

; EDNS: version: 0, flags: do; udp: 4096
;www.greenfly.org.              IN      A

www.greenfly.org.       900     IN      A
www.greenfly.org.       900     IN      RRSIG   A 5 3 900 20130523213855
20130423213855 58317 greenfly.org.
7LzmEumdAVM2MmrPVu+PKGfilPlfofjwJLbgVhyYqepbbD8xv3bmg0Np YnM=

greenfly.org.           900     IN      NS      ns2.greenfly.org.
greenfly.org.           900     IN      NS      ns1.greenfly.org.
greenfly.org.           900     IN      RRSIG   NS 5 2 900 20130523213855
20130423213855 58317 greenfly.org.
BqmNIHzROZkf6BOrx6Nqv65npSGoNLQBoEc90FvDFe/N5I27LBTIxCv4 3UQ=

ns1.greenfly.org.       900     IN      A
ns2.greenfly.org.       900     IN      A
ns1.greenfly.org.       900     IN      RRSIG   A 5 3 900 20130523213855
20130423213855 58317 greenfly.org.
Rp01qVkeBIZ7g+K7LY2XRU3DGSzbeFUKrViqtakbTQxZ9o3Oj6ZqL0Pv 0nQ=
ns2.greenfly.org.       900     IN      RRSIG   A 5 3 900 20130523213855
20130423213855 58317 greenfly.org.
UcSSD7wft9YO7UTIiQrc8LkItXZAKd72Gy1ZP4mhhLxwwOIhlHshQ9d2 uTY=

;; Query time: 196 msec
;; WHEN: Fri Apr 26 16:13:22 2013
;; MSG SIZE  rcvd: 817

Tell Your Parent

The final step once you have confirmed that DNSSEC is returning signed records for your zone is to go to your zone's parent (typically through the registrar you used to buy the domain to begin with) and provide them with the DS record (in that dsset-zonename file that dnssec-signzone generated) so they can sign it. Unfortunately, only a small number of registrars provide DNSSEC support today, and some charge extra for the service. In either case, you may want to use DLV instead via a service like dlv.isc.org. To do that, simply visit https://dlv.isc.org and follow the instructions to create an account and register your zone with them. They provide a simple interface that validates DNSSEC on your zone and even will send you alerts if you forget to update your zone's signatures after a month.

So, although enabling DNSSEC isn't as simple as a regular BIND configuration (and to many people even that is pretty complicated), it's also not all that difficult once you know the proper steps. Hopefully, this column has encouraged you to try out DNSSEC on your zones.


Kyle Rankin is Chief Security Officer at Purism, a company focused on computers that respect your privacy, security, and freedom. He is the author of many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu