# DNSSEC, Dynamic Zones, and Automatic Signing

As of BIND 9.7.0 it is possible to change a dynamic zone from insecure to signed and back again. A secure zone can use either NSEC or NSEC3 chains.

## Converting from insecure to secure

Changing a zone from insecure to secure can be done in two ways: using a dynamic DNS update, or the `auto-dnssec` zone option.

For either method, you need to configure `named` so that it can see the `K*` files which contain the public and private parts of the keys that will be used to sign the zone. These files will have been generated by `dnssec-keygen`. You can do this by placing them in the key-directory, as specified in `named.conf`:

            zone example.net {
                    type master;
                    update-policy local;
                    file "dynamic/example.net/example.net";
                    key-directory "dynamic/example.net";
            };

If one KSK and one ZSK DNSKEY key have been generated, this configuration will cause all records in the zone to be signed with the ZSK, and the DNSKEY RRset to be signed with the KSK as well. An NSEC chain will be generated as part of the initial signing process.

## Dynamic DNS update method

To insert the keys via dynamic update:

            % nsupdate
            > ttl 3600
            > update add example.net DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8=
            > update add example.net DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk=
            > send

While the update request will complete almost immediately, the zone will not be completely signed until `named` has had time to walk the zone and generate the NSEC and RRSIG records. The NSEC record at the apex will be added last, to signal that there is a complete NSEC chain.

If you wish to sign using NSEC3 instead of NSEC, you should add an NSEC3PARAM record to the initial update request. If you wish the NSEC3 chain to have the OPTOUT bit set, set it in the flags field of the NSEC3PARAM record.

            % nsupdate
            > ttl 3600
            > update add example.net DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8=
            > update add example.net DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk=
            > update add example.net NSEC3PARAM 1 1 100 1234567890
            > send

Again, this update request will complete almost immediately; however, the record won't show up until `named` has had a chance to build/remove the relevant chain. A private type record will be created to record the state of the operation (see below for more details), and will be removed once the operation completes.

While the initial signing and NSEC/NSEC3 chain generation is happening, other updates are possible as well.

## Fully automatic zone signing

To enable automatic signing, add the `auto-dnssec` option to the zone statement in `named.conf`. `auto-dnssec` has two possible arguments: `allow` or `maintain`.

With `auto-dnssec allow`, `named` can search the key directory for keys matching the zone, insert them into the zone, and use them to sign the zone. It will do so only when it receives an `rndc sign <zonename>` or `rndc loadkeys <zonename>` command.

`auto-dnssec maintain` includes the above functionality, but will also automatically adjust the zone's DNSKEY records on schedule according to the keys' timing metadata. (See and for more information.) If keys are present in the key directory the first time the zone is loaded, it will be signed immediately, without waiting for an `rndc sign` or `rndc loadkeys` command. (Those commands can still be used when there are unscheduled key changes, however.)

Using the `auto-dnssec` option requires the zone to be configured to allow dynamic updates, by adding an `allow-update` or `update-policy` statement to the zone configuration. If this has not been done, the configuration will fail.

## Private-type records

The state of the signing process is signaled by private-type records (with a default type value of 65534). When signing is complete, these records will have a nonzero value for the final octet (for those records which have a nonzero initial octet).

The private type record format: If the first octet is non-zero then the record indicates that the zone needs to be signed with the key matching the record, or that all signatures that match the record should be removed.

      algorithm (octet 1)
      key id in network order (octet 2 and 3)
      removal flag (octet 4)
      complete flag (octet 5)

Only records flagged as "complete" can be removed via dynamic update. Attempts to remove other private type records will be silently ignored.

If the first octet is zero (this is a reserved algorithm number that should never appear in a DNSKEY record) then the record indicates changes to the NSEC3 chains are in progress. The rest of the record contains an NSEC3PARAM record. The flag field tells what operation to perform based on the flag bits.

      0x01 OPTOUT
      0x80 CREATE
      0x40 REMOVE
      0x20 NONSEC

## DNSKEY rollovers

As with insecure-to-secure conversions, rolling DNSSEC keys can be done in two ways: using a dynamic DNS update, or the `auto-dnssec` zone option.

## Dynamic DNS update method

To perform key rollovers via dynamic update, you need to add the `K*` files for the new keys so that `named` can find them. You can then add the new DNSKEY RRs via dynamic update. `named` will then cause the zone to be signed with the new keys. When the signing is complete the private type records will be updated so that the last octet is non zero.

If this is for a KSK you need to inform the parent and any trust anchor repositories of the new KSK.

You should then wait for the maximum TTL in the zone before removing the old DNSKEY. If it is a KSK that is being updated, you also need to wait for the DS RRset in the parent to be updated and its TTL to expire. This ensures that all clients will be able to verify at least one signature when you remove the old DNSKEY.

The old DNSKEY can be removed via UPDATE. Take care to specify the correct key. `named` will clean out any signatures generated by the old key after the update completes.

## Automatic key rollovers

When a new key reaches its activation date (as set by `dnssec-keygen` or `dnssec-settime`), if the `auto-dnssec` zone option is set to `maintain`, `named` will automatically carry out the key rollover. If the key's algorithm has not previously been used to sign the zone, then the zone will be fully signed as quickly as possible. However, if the new key is replacing an existing key of the same algorithm, then the zone will be re-signed incrementally, with signatures from the old key being replaced with signatures from the new key as their signature validity periods expire. By default, this rollover completes in 30 days, after which it will be safe to remove the old key from the DNSKEY RRset.

## NSEC3PARAM rollovers via UPDATE

Add the new NSEC3PARAM record via dynamic update. When the new NSEC3 chain has been generated, the NSEC3PARAM flag field will be zero. At this point you can remove the old NSEC3PARAM record. The old chain will be removed after the update request completes.

## Converting from NSEC to NSEC3

To do this, you just need to add an NSEC3PARAM record. When the conversion is complete, the NSEC chain will have been removed and the NSEC3PARAM record will have a zero flag field. The NSEC3 chain will be generated before the NSEC chain is destroyed.

## Converting from NSEC3 to NSEC

To do this, use `nsupdate` to remove all NSEC3PARAM records with a zero flag field. The NSEC chain will be generated before the NSEC3 chain is removed.

## Converting from secure to insecure

To convert a signed zone to unsigned using dynamic DNS, delete all the DNSKEY records from the zone apex using `nsupdate`. All signatures, NSEC or NSEC3 chains, and associated NSEC3PARAM records will be removed automatically. This will take place after the update request completes.

This requires the `dnssec-secure-to-insecure` option to be set to `yes` in `named.conf`.

In addition, if the `auto-dnssec maintain` zone statement is used, it should be removed or changed to `allow` instead (or it will re-sign).

## Periodic re-signing

In any secure zone which supports dynamic updates, named will periodically re-sign RRsets which have not been re-signed as a result of some update action. The signature lifetimes will be adjusted so as to spread the re-sign load over time rather than all at once.

## NSEC3 and OPTOUT

`named` only supports creating new NSEC3 chains where all the NSEC3 records in the zone have the same OPTOUT state. `named` supports UPDATES to zones where the NSEC3 records in the chain have mixed OPTOUT state. `named` does not support changing the OPTOUT state of an individual NSEC3 record, the entire chain needs to be changed if the OPTOUT state of an individual NSEC3 needs to be changed.