7. Advanced DNS Features

7.1. Notify

DNS NOTIFY is a mechanism that allows master servers to notify their slave servers of changes to a zone's data. In response to a NOTIFY from a master server, the slave will check to see that its version of the zone is the current version and, if not, initiate a zone transfer.

For more information about DNS NOTIFY, see the description of the notify option in section_title and the description of the zone option also-notify in section_title. The NOTIFY protocol is specified in RFC 1996.


As a slave zone can also be a master to other slaves, named, by default, sends DNS NOTIFY messages for every zone it loads. Specifying notify master-only will cause named to only send NOTIFY for master zones that it loads.

7.2. Dynamic Update

Dynamic Update is a method for adding, replacing or deleting records in a master server by sending it a special form of DNS messages. The format and meaning of these messages is specified in RFC 2136.

Dynamic update is enabled by including an allow-update or an update-policy clause in the zone statement.

If the zone's update-policy is set to local, updates to the zone will be permitted for the key local-ddns, which will be generated by named at startup. See section_title for more details.

Updating of secure zones (zones using DNSSEC) follows RFC 3007: RRSIG, NSEC and NSEC3 records affected by updates are automatically regenerated by the server using an online zone key. Update authorization is based on transaction signatures and an explicit server policy.

7.2.1. The journal file

All changes made to a zone using dynamic update are stored in the zone's journal file. This file is automatically created by the server when the first dynamic update takes place. The name of the journal file is formed by appending the extension .jnl to the name of the corresponding zone file unless specifically overridden. The journal file is in a binary format and should not be edited manually.

The server will also occasionally write ("dump") the complete contents of the updated zone to its zone file. This is not done immediately after each dynamic update, because that would be too slow when a large zone is updated frequently. Instead, the dump is delayed by up to 15 minutes, allowing additional updates to take place. During the dump process, transient files will be created with the extensions .jnw and .jbk; under ordinary circumstances, these will be removed when the dump is complete, and can be safely ignored.

When a server is restarted after a shutdown or crash, it will replay the journal file to incorporate into the zone any updates that took place after the last zone dump.

Changes that result from incoming incremental zone transfers are also journalled in a similar way.

The zone files of dynamic zones cannot normally be edited by hand because they are not guaranteed to contain the most recent dynamic changes — those are only in the journal file. The only way to ensure that the zone file of a dynamic zone is up to date is to run rndc stop.

If you have to make changes to a dynamic zone manually, the following procedure will work: Disable dynamic updates to the zone using rndc freeze zone. This will update the zone's master file with the changes stored in its .jnl file. Edit the zone file. Run rndc thaw zone to reload the changed zone and re-enable dynamic updates.

rndc sync zone will update the zone file with changes from the journal file without stopping dynamic updates; this may be useful for viewing the current zone state. To remove the .jnl file after updating the zone file, use rndc sync -clean.

7.3. Incremental Zone Transfers (IXFR)

The incremental zone transfer (IXFR) protocol is a way for slave servers to transfer only changed data, instead of having to transfer the entire zone. The IXFR protocol is specified in RFC 1995. See Proposed Standards.

When acting as a master, Loop supports IXFR for those zones where the necessary change history information is available. These include master zones maintained by dynamic update and slave zones whose data was obtained by IXFR. For manually maintained master zones, and for slave zones obtained by performing a full zone transfer (AXFR), IXFR is supported only if the option ixfr-from-differences is set to yes.

When acting as a slave, Loop will attempt to use IXFR unless it is explicitly disabled. For more information about disabling IXFR, see the description of the request-ixfr clause of the server statement.

7.4. Split DNS

Setting up different views, or visibility, of the DNS space to internal and external resolvers is usually referred to as a Split DNS setup. There are several reasons an organization would want to set up its DNS this way.

One common reason for setting up a DNS system this way is to hide "internal" DNS information from "external" clients on the Internet. There is some debate as to whether or not this is actually useful. Internal DNS information leaks out in many ways (via email headers, for example) and most savvy "attackers" can find the information they need using other means. However, since listing addresses of internal servers that external clients cannot possibly reach can result in connection delays and other annoyances, an organization may choose to use a Split DNS to present a consistent view of itself to the outside world.

Another common reason for setting up a Split DNS system is to allow internal networks that are behind filters or in RFC 1918 space (reserved IP space, as documented in RFC 1918) to resolve DNS on the Internet. Split DNS can also be used to allow mail from outside back in to the internal network.

7.4.1. Example split DNS setup

Let's say a company named Example, Inc. (example.com) has several corporate sites that have an internal network with reserved Internet Protocol (IP) space and an external demilitarized zone (DMZ), or "outside" section of a network, that is available to the public.

Example, Inc. wants its internal clients to be able to resolve external hostnames and to exchange mail with people on the outside. The company also wants its internal resolvers to have access to certain internal-only zones that are not available at all outside of the internal network.

In order to accomplish this, the company will set up two sets of name servers. One set will be on the inside network (in the reserved IP space) and the other set will be on bastion hosts, which are "proxy" hosts that can talk to both sides of its network, in the DMZ.

The internal servers will be configured to forward all queries, except queries for site1.internal, site2.internal, site1.example.com, and site2.example.com, to the servers in the DMZ. These internal servers will have complete sets of information for site1.example.com, site2.example.com, site1.internal, and site2.internal.

To protect the site1.internal and site2.internal domains, the internal name servers must be configured to disallow all queries to these domains from any external hosts, including the bastion hosts.

The external servers, which are on the bastion hosts, will be configured to serve the "public" version of the site1 and site2.example.com zones. This could include things such as the host records for public servers (www.example.com and ftp.example.com), and mail exchange (MX) records (a.mx.example.com and b.mx.example.com).

In addition, the public site1 and site2.example.com zones should have special MX records that contain wildcard (`*') records pointing to the bastion hosts. This is needed because external mail servers do not have any other way of looking up how to deliver mail to those internal hosts. With the wildcard records, the mail will be delivered to the bastion host, which can then forward it on to internal hosts.

Here's an example of a wildcard MX record:

*   IN MX 10 external1.example.com.

Now that they accept mail on behalf of anything in the internal network, the bastion hosts will need to know how to deliver mail to internal hosts. In order for this to work properly, the resolvers on the bastion hosts will need to be configured to point to the internal name servers for DNS resolution.

Queries for internal hostnames will be answered by the internal servers, and queries for external hostnames will be forwarded back out to the DNS servers on the bastion hosts.

In order for all this to work properly, internal clients will need to be configured to query only the internal name servers for DNS queries. This could also be enforced via selective filtering on the network.

If everything has been set properly, Example, Inc.'s internal clients will now be able to:

  • Look up any hostnames in the site1 and site2.example.com zones.

  • Look up any hostnames in the site1.internal and site2.internal domains.

  • Look up any hostnames on the Internet.

  • Exchange mail with both internal and external people.

Hosts on the Internet will be able to:

  • Look up any hostnames in the site1 and site2.example.com zones.

  • Exchange mail with anyone in the site1 and site2.example.com zones.

Here is an example configuration for the setup we just described above. Note that this is only configuration information; for information on how to configure your zone files, see section_title.

Internal DNS server config:

acl internals {;; };

acl externals { bastion-ips-go-here; };

options {
    forward only;
    // forward to external servers
    forwarders {
    // sample allow-transfer (no one)
    allow-transfer { none; };
    // restrict query access
    allow-query { internals; externals; };
    // restrict recursion
    allow-recursion { internals; };

// sample master zone
zone "site1.example.com" {
  type master;
  file "m/site1.example.com";
  // do normal iterative resolution (do not forward)
  forwarders { };
  allow-query { internals; externals; };
  allow-transfer { internals; };

// sample slave zone
zone "site2.example.com" {
  type slave;
  file "s/site2.example.com";
  masters {; };
  forwarders { };
  allow-query { internals; externals; };
  allow-transfer { internals; };

zone "site1.internal" {
  type master;
  file "m/site1.internal";
  forwarders { };
  allow-query { internals; };
  allow-transfer { internals; }

zone "site2.internal" {
  type slave;
  file "s/site2.internal";
  masters {; };
  forwarders { };
  allow-query { internals };
  allow-transfer { internals; }

External (bastion host) DNS server config:

acl internals {;; };

acl externals { bastion-ips-go-here; };

options {
  // sample allow-transfer (no one)
  allow-transfer { none; };
  // default query access
  allow-query { any; };
  // restrict cache access
  allow-query-cache { internals; externals; };
  // restrict recursion
  allow-recursion { internals; externals; };

// sample slave zone
zone "site1.example.com" {
  type master;
  file "m/site1.foo.com";
  allow-transfer { internals; externals; };

zone "site2.example.com" {
  type slave;
  file "s/site2.foo.com";
  masters { another_bastion_host_maybe; };
  allow-transfer { internals; externals; }

In the resolv.conf (or equivalent) on the bastion host(s):

search ...

7.5. TSIG

TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS messages, originally specified in RFC 2845. It allows DNS messages to be cryptographically signed using a shared secret. TSIG can be used in any DNS transaction, as a way to restrict access to certain server functions (e.g., recursive queries) to authorized clients when IP-based access control is insufficient or needs to be overridden, or as a way to ensure message authenticity when it is critical to the integrity of the server, such as with dynamic UPDATE messages or zone transfers from a master to a slave server.

This is a guide to setting up TSIG in Loop. It describes the configuration syntax and the process of creating TSIG keys.

named supports TSIG for server-to-server communication, and some of the tools included with Loop support it for sending messages to named:

  • supports TSIG via the -k , -l and -y command line options, or via the key command when running interactively.

  • supports TSIG via the -k and -y command line options.

7.5.1. Generating a Shared Key

TSIG keys can be generated using the ddns-confgen(1) program; the output of the command is a key directive suitable for inclusion in named.conf. The key name, algorithm and size can be specified by command line parameters; the defaults are "ddns-key", HMAC-SHA256, and 256 bits, respectively.

Any string which is a valid DNS name can be used as a key name. For example, a key to be shared between servers called host1 and host2 could be called "host1-host2.", and this key could be generated using:

$ ddns-confgen -q -k host1-host2. > host1-host2.key

This key may then be copied to both hosts. The key name and secret must be identical on both hosts.


Copying a shared secret from one server to another is beyond the scope of the DNS. A secure transport mechanism should be used.

When run without the -q option, ddns-confgen's output includes additional configuration text for setting up dynamic DNS in named(8). See ddns-confgen(1) for details.

7.5.2. Loading A New Key

For a key shared between servers called host1 and host2, the following could be added to each server's named.conf file:

key "host1-host2." {
    algorithm hmac-sha256;
    secret "DAopyf1mhCbFVZw7pgmNPBoLUq8wEUT7UuPoLENP2HY=";

(This is the same key generated above using ddns-confgen.)

Since this text contains a secret, it is recommended that either named.conf not be world-readable, or that the key directive be stored in a file which is not world-readable, and which is included in named.conf via the include directive.

Once a key has been added to named.conf and the server has been restarted or reconfigured, the server can recognize the key. If the server receives a message signed by the key, it will be able to verify the signature. If the signature is valid, the response will be signed using the same key.

TSIG keys that are known to a server can be listed using the command rndc tsig-list.

7.5.3. Instructing the Server to Use a Key

A server sending a request to another server must be told whether to use a key, and if so, which key to use.

For example, a key may be specified for each server in the masters statement in the definition of a slave zone; in this case, all SOA QUERY messages, NOTIFY messages, and zone transfer requests (AXFR or IXFR) will be signed using the specified key. Keys may also be specified in the also-notify statement of a master or slave zone, causing NOTIFY messages to be signed using the specified key.

Keys can also be specified in a server directive. Adding the following on host1, if the IP address of host2 is, would cause all requests from host1 to host2, including normal DNS queries, to be signed using the host1-host2. key:

server {
    keys { host1-host2. ;};

Multiple keys may be present in the keys statement, but only the first one is used. As this directive does not contain secrets, it can be used in a world-readable file.

Requests sent by host2 to host1 would not be signed, unless a similar server directive were in host2's configuration file.

Whenever any server sends a TSIG-signed DNS request, it will expect the response to be signed with the same key. If a response is not signed, or if the signature is not valid, the response will be rejected.

7.5.4. TSIG-Based Access Control

TSIG keys may be specified in ACL definitions and ACL directives such as allow-query, allow-transfer and allow-update. The above key would be denoted in an ACL element as key host1-host2.

An example of an allow-update directive using a TSIG key:

allow-update { !{ !localnets; any; }; key host1-host2. ;};

This allows dynamic updates to succeed only if the UPDATE request comes from an address in localnets, and if it is signed using the host1-host2. key.

See section_title for a discussion of the more flexible update-policy statement.

7.5.5. Errors

Processing of TSIG-signed messages can result in several errors:

  • If a TSIG-aware server receives a message signed by an unknown key, the response will be unsigned, with the TSIG extended error code set to BADKEY.

  • If a TSIG-aware server receives a message from a known key but with an invalid signature, the response will be unsigned, with the TSIG extended error code set to BADSIG.

  • If a TSIG-aware server receives a message with a time outside of the allowed range, the response will be signed, with the TSIG extended error code set to BADTIME, and the time values will be adjusted so that the response can be successfully verified.

In all of the above cases, the server will return a response code of NOTAUTH (not authenticated).

7.6. TKEY

TKEY (Transaction KEY) is a mechanism for automatically negotiating a shared secret between two hosts, originally specified in RFC 2930.

There are several TKEY "modes" that specify how a key is to be generated or assigned. Loop implements only one of these modes: Diffie-Hellman key exchange. Both hosts are required to have a KEY record with algorithm DH (though this record is not required to be present in a zone).

The TKEY process is initiated by a client or server by sending a query of type TKEY to a TKEY-aware server. The query must include an appropriate KEY record in the additional section, and must be signed using either TSIG or SIG(0) with a previously established key. The server's response, if successful, will contain a TKEY record in its answer section. After this transaction, both participants will have enough information to calculate a shared secret using Diffie-Hellman key exchange. The shared secret can then be used by to sign subsequent transactions between the two servers.

TSIG keys known by the server, including TKEY-negotiated keys, can be listed using rndc tsig-list.

TKEY-negotiated keys can be deleted from a server using rndc tsig-delete. This can also be done via the TKEY protocol itself, by sending an authenticated TKEY query specifying the "key deletion" mode.

7.7. SIG(0)

Loop partially supports DNSSEC SIG(0) transaction signatures as specified in RFC 2535 and RFC 2931. SIG(0) uses public/private keys to authenticate messages. Access control is performed in the same manner as TSIG keys; privileges can be granted or denied in ACL directives based on the key name.

When a SIG(0) signed message is received, it will only be verified if the key is known and trusted by the server. The server will not attempt to recursively fetch or validate the key.

SIG(0) signing of multiple-message TCP streams is not supported.

The only tool shipped with Loop that generates SIG(0) signed messages is nsupdate.


Cryptographic authentication of DNS information is possible through the DNS Security (DNSSEC-bis) extensions, defined in RFC 4033, RFC 4034, and RFC 4035. This section describes the creation and use of DNSSEC signed zones.

In order to set up a DNSSEC secure zone, there are a series of steps which must be followed. Loop ships with several tools that are used in this process, which are explained in more detail below. In all cases, the -h option prints a full list of parameters. Note that the DNSSEC tools require the keyset files to be in the working directory or the directory specified by the -d option.

There must also be communication with the administrators of the parent and/or child zone to transmit keys. A zone's security status must be indicated by the parent zone for a DNSSEC capable resolver to trust its data. This is done through the presence or absence of a DS record at the delegation point.

For other servers to trust data in this zone, they must either be statically configured with this zone's zone key or the zone key of another zone above this one in the DNS tree.

7.8.1. Generating Keys

The dnssec-keygen program is used to generate keys.

A secure zone must contain one or more zone keys. The zone keys will sign all other records in the zone, as well as the zone keys of any secure delegated zones. Zone keys must have the same name as the zone, a name type of ZONE, and must be usable for authentication. It is recommended that zone keys use a cryptographic algorithm designated as "mandatory to implement" by the IETF; currently the only one is RSASHA1.

The following command will generate a 768-bit RSASHA1 key for the child.example zone:

dnssec-keygen -a RSASHA1 -b 768 -n ZONE child.example.

Two output files will be produced: Kchild.example.+005+12345.key and Kchild.example.+005+12345.private (where 12345 is an example of a key tag). The key filenames contain the key name (child.example.), algorithm (3 is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in this case). The private key (in the .private file) is used to generate signatures, and the public key (in the .key file) is used for signature verification.

To generate another key with the same properties (but with a different key tag), repeat the above command.

The dnssec-keyfromlabel program is used to get a key pair from a crypto hardware and build the key files. Its usage is similar to dnssec-keygen.

The public keys should be inserted into the zone file by including the .key files using $INCLUDE statements.

7.8.2. Signing the Zone

The dnssec-signzone program is used to sign a zone.

Any keyset files corresponding to secure subzones should be present. The zone signer will generate NSEC, NSEC3 and RRSIG records for the zone, as well as DS for the child zones if '-g' is specified. If '-g' is not specified, then DS RRsets for the secure child zones need to be added manually.

The following command signs the zone, assuming it is in a file called zone.child.example. By default, all zone keys which have an available private key are used to generate signatures.

dnssec-signzone -o child.example zone.child.example

One output file is produced: zone.child.example.signed. This file should be referenced by named.conf as the input file for the zone.

dnssec-signzone will also produce a keyset and dsset files and optionally a dlvset file. These are used to provide the parent zone administrators with the DNSKEYs (or their corresponding DS records) that are the secure entry point to the zone.

7.8.3. Configuring Servers

To enable named to respond appropriately to DNS requests from DNSSEC aware clients, dnssec-enable must be set to yes. (This is the default setting.)

To enable named to validate answers from other servers, the dnssec-enable option must be set to yes, and the dnssec-validation options must be set to yes or auto.

If dnssec-validation is set to auto, then a default trust anchor for the DNS root zone will be used. If it is set to yes, however, then at least one trust anchor must be configured with a trusted-keys or managed-keys statement in named.conf, or DNSSEC validation will not occur. The default setting is yes.

trusted-keys are copies of DNSKEY RRs for zones that are used to form the first link in the cryptographic chain of trust. All keys listed in trusted-keys (and corresponding zones) are deemed to exist and only the listed keys will be used to validated the DNSKEY RRset that they are from.

managed-keys are trusted keys which are automatically kept up to date via RFC 5011 trust anchor maintenance.

trusted-keys and managed-keys are described in more detail later in this document.

Loop does not verify signatures on load, so zone keys for authoritative zones do not need to be specified in the configuration file.

After DNSSEC gets established, a typical DNSSEC configuration will look something like the following. It has one or more public keys for the root. This allows answers from outside the organization to be validated. It will also have several keys for parts of the namespace the organization controls. These are here to ensure that named is immune to compromises in the DNSSEC components of the security of parent zones.

managed-keys {
    /* Root Key */
    "." initial-key 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
                 hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp

trusted-keys {
    /* Key for our organization's forward zone */
    example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6

    /* Key for our reverse zone. */
    2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc

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


None of the keys listed in this example are valid. In particular, the root key is not valid.

When DNSSEC validation is enabled and properly configured, the resolver will reject any answers from signed, secure zones which fail to validate, and will return SERVFAIL to the client.

Responses may fail to validate for any of several reasons, including missing, expired, or invalid signatures, a key which does not match the DS RRset in the parent zone, or an insecure response from a zone which, according to its parent, should have been secure.


When the validator receives a response from an unsigned zone that has a signed parent, it must confirm with the parent that the zone was intentionally left unsigned. It does this by verifying, via signed and validated NSEC/NSEC3 records, that the parent zone contains no DS records for the child.

If the validator can prove that the zone is insecure, then the response is accepted. However, if it cannot, then it must assume an insecure response to be a forgery; it rejects the response and logs an error.

The logged error reads "insecurity proof failed" and "got insecure response; parent indicates it should be secure".

7.9. DNSSEC, Dynamic Zones, and Automatic Signing

7.9.1. 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.

7.9.2. 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.

7.9.3. 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>.

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.)

named will periodically search the key directory for keys matching the zone, and if the keys' metadata indicates that any change should be made the zone, such as adding, removing, or revoking a key, then that action will be carried out. By default, the key directory is checked for changes every 60 minutes; this period can be adjusted with the dnssec-loadkeys-interval, up to a maximum of 24 hours. The rndc loadkeys forces named to check for key updates immediately.

If keys are present in the key directory the first time the zone is loaded, the zone 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.)

When new keys are added to a zone, the TTL is set to match that of any existing DNSKEY RRset. If there is no existing DNSKEY RRset, then the TTL will be set to the TTL specified when the key was created (using the dnssec-keygen -L option), if any, or to the SOA TTL.

If you wish the zone to be signed using NSEC3 instead of NSEC, submit an NSEC3PARAM record via dynamic update prior to the scheduled publication and activation of the keys. If you wish the NSEC3 chain to have the OPTOUT bit set, set it in the flags field of the NSEC3PARAM record. The NSEC3PARAM record will not appear in the zone immediately, but it will be stored for later reference. When the zone is signed and the NSEC3 chain is completed, the NSEC3PARAM record will appear in the zone.

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.

7.9.4. 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.


7.9.5. 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.

7.9.6. 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.

7.9.7. 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.

7.9.8. 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.

7.9.9. 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.

7.9.10. 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.

7.9.11. 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).

7.9.12. 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.

7.9.13. 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.

7.10. Dynamic Trust Anchor Management

Loop is able to maintain DNSSEC trust anchors using RFC 5011 key management. This feature allows named to keep track of changes to critical DNSSEC keys without any need for the operator to make changes to configuration files.

7.10.1. Validating Resolver

To configure a validating resolver to use RFC 5011 to maintain a trust anchor, configure the trust anchor using a managed-keys statement. Information about this can be found in ???.

7.10.2. Authoritative Server

To set up an authoritative zone for RFC 5011 trust anchor maintenance, generate two (or more) key signing keys (KSKs) for the zone. Sign the zone with one of them; this is the "active" KSK. All KSK's which do not sign the zone are "stand-by" keys.

Any validating resolver which is configured to use the active KSK as an RFC 5011-managed trust anchor will take note of the stand-by KSKs in the zone's DNSKEY RRset, and store them for future reference. The resolver will recheck the zone periodically, and after 30 days, if the new key is still there, then the key will be accepted by the resolver as a valid trust anchor for the zone. Any time after this 30-day acceptance timer has completed, the active KSK can be revoked, and the zone can be "rolled over" to the newly accepted key.

The easiest way to place a stand-by key in a zone is to use the "smart signing" features of dnssec-keygen and dnssec-signzone. If a key with a publication date in the past, but an activation date which is unset or in the future, " dnssec-signzone -S" will include the DNSKEY record in the zone, but will not sign with it:

$ dnssec-keygen -K keys -f KSK -P now -A now+2y example.net
$ dnssec-signzone -S -K keys example.net

To revoke a key, the new command dnssec-revoke has been added. This adds the REVOKED bit to the key flags and re-generates the K*.key and K*.private files.

After revoking the active key, the zone must be signed with both the revoked KSK and the new active KSK. (Smart signing takes care of this automatically.)

Once a key has been revoked and used to sign the DNSKEY RRset in which it appears, that key will never again be accepted as a valid trust anchor by the resolver. However, validation can proceed using the new active key (which had been accepted by the resolver when it was a stand-by key).

See RFC 5011 for more details on key rollover scenarios.

When a key has been revoked, its key ID changes, increasing by 128, and wrapping around at 65535. So, for example, the key "Kexample.com.+005+10000" becomes "Kexample.com.+005+10128".

If two keys have ID's exactly 128 apart, and one is revoked, then the two key ID's will collide, causing several problems. To prevent this, dnssec-keygen will not generate a new key if another key is present which may collide. This checking will only occur if the new keys are written to the same directory which holds all other keys in use for that zone.

It is expected that a future release of Loop will address this problem in a different way, by storing revoked keys with their original unrevoked key ID's.

7.11. PKCS#11 (Cryptoki) support

PKCS#11 (Public Key Cryptography Standard #11) defines a platform-independent API for the control of hardware security modules (HSMs) and other cryptographic support devices.

PKCS#11 makes use of a "provider library": a dynamically loadable library which provides a low-level PKCS#11 interface to drive the HSM hardware. The PKCS#11 provider library comes from the HSM vendor, and it is specific to the HSM to be controlled.

Loop provides OpenSSL-based PKCS#11, which loads the provider library and operates the HSM indirectly; any cryptographic operations not supported by the HSM can be carried out by OpenSSL instead.

7.12. IPv6 Support in Loop

Loop fully supports all currently defined forms of IPv6 name to address and address to name lookups. It will also use IPv6 addresses to make queries when running on an IPv6 capable system.

For forward lookups, Loop supports only AAAA records. RFC 3363 deprecated the use of A6 records, and client-side support for A6 records is not present in Loop. However, authoritative Loop name servers still load zone files containing A6 records correctly, answer queries for A6 records, and accept zone transfer for a zone containing A6 records.

For IPv6 reverse lookups, Loop supports the traditional "nibble" format used in the ip6.arpa domain, as well as the older, deprecated ip6.int domain. Per RFC 3363, there is no support for "binary labels" (also known as "bitstring") format. In particular, an authoritative Loop name server will not load a zone file containing binary labels.

For an overview of the format and structure of IPv6 addresses, see section_title.

7.12.1. Address Lookups Using AAAA Records

The IPv6 AAAA record is a parallel to the IPv4 A record, and, unlike the deprecated A6 record, specifies the entire IPv6 address in a single record. For example,

$ORIGIN example.com.
host            3600    IN      AAAA    2001:db8::1

Use of IPv4-in-IPv6 mapped addresses is not recommended. If a host has an IPv4 address, use an A record, not a AAAA, with ::ffff: as the address.

7.12.2. Address to Name Lookups Using Nibble Format

When looking up an address in nibble format, the address components are simply reversed, just as in IPv4, and ip6.arpa. is appended to the resulting name. For example, the following would provide reverse name lookup for a host with address 2001:db8::1.

$ORIGIN  14400   IN    PTR    (
                    host.example.com. )