Table of Contents
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 the section called “Boolean Options” and the description of the zone option also-notify in the section called “Zone Transfers”. The NOTIFY protocol is specified in RFC 1996.
As a slave zone can also be a master to other slaves, named, by default, sends NOTIFY messages for every zone it loads. Specifying notify master-only; will cause named to only send NOTIFY for master zones that it loads.
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 the section called “Dynamic Update Policies” for more details.
Dynamic updates using Kerberos signed requests can be made using the TKEY/GSS protocol by setting either the tkey-gssapi-keytab option, or alternatively by setting both the tkey-gssapi-credential and tkey-domain options. Once enabled, Kerberos signed requests will be matched against the update policies for the zone, using the Kerberos principal as the signer for the request.
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.
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.
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, BIND 9
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, BIND 9 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.
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.
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:
site1
and
site2.example.com zones.
site1.internal and
site2.internal domains.
Hosts on the Internet will be able to:
site1
and
site2.example.com zones.
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 the section called “Sample Configurations”.
Internal DNS server config:
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
forward only;
// forward to external servers
forwarders {
bastion-ips-go-here;
};
// 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 { 172.16.72.3; };
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 { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
External (bastion host) DNS server config:
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
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 ... nameserver 172.16.72.2 nameserver 172.16.72.3 nameserver 172.16.72.4
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 BIND. 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 BIND support it for sending messages to named:
-k, -l and
-y command line options, or via
the key command when running
interactively.
-k and -y command
line options.
TSIG keys can be generated using the ddns-confgen
command; the output of the command is a key directive
suitable for inclusion in named.conf. The
key name and algorithm can be specified by command line parameters;
the defaults are "ddns-key" and HMAC-SHA256, respectively. By
default, the output of ddns-confgen also includes
additional configuration text for setting up dynamic DNS in
named; the -q suppresses
this. See ddns-confgen(8) for further details.
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. (Note: copying a shared secret from one server to another is beyond the scope of the DNS. A secure transport mechanism should be used: secure FTP, SSL, ssh, telephone, encrypted email, etc.)
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.
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 10.1.2.3, would cause all requests from host1 to host2, including normal DNS queries, to be signed using the host1-host2. key:
server 10.1.2.3 {
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.
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 the section called “Dynamic Update Policies” for a discussion of the more flexible update-policy statement.
Processing of TSIG-signed messages can result in several errors:
In all of the above cases, the server will return a response code of NOTAUTH (not authenticated).
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. BIND 9 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.
BIND 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 BIND 9 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. BIND
9 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, and
that the tools shipped with BIND 9.2.x and earlier are not compatible
with the current ones.
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.
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.
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.
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.
Unlike BIND 8, BIND 9 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
JxrGkxJWoZu6I7PzJu/E9gx4UC1zGAHlXKdE4zYIpRh
aBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3zy2Xy
4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYg
hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M/lUUVRbke
g1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq
66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
97S+LKUTpQcq27R7AT3/V5hRQxScINqwcz4jYqZD2fQ
dgxbcDTClU0CRBdiieyLMNzXG3";
};
trusted-keys {
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
kBOUKUf/mC7HvfwYH/Be22GnClrinKJp1O
g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
FxmAVZP20igTixin/1LcrgX/KMEGd/biuv
F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
/oyWR8BW/hWdzOvnSCThlHf3xiYleDbt/o
1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc
xOdNax071L18QqZnQQQAVVr+i
LhGTnNGp3HoWQLUIzKrJVZ3zg
gy3WwNT6kZo6c0tszYqbtvchm
gQC8CzKojM/W16i6MG/eafGU3
siaOdS0yOI6BgPsw+YZdzlYMa
IJGf4M4dyoKIhzdZyQ2bYQrjy
Q4LB0lC7aOnsMyYKHHYeRvPxj
IQXmdqgOJGq+vsevG06zW+1xg
YJh9rCIfnm1GX/KMgxLPG2vXT
D/RnLX+D3T3UL7HJYHJhAZD5L
59VvjSPsZJHeDCUyWYrvPZesZ
DIRvhDD52SKvbheeTJUm6Ehkz
ytNN2SN96QRk8j/iI8ib";
};
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". (Prior to BIND 9.7, the logged error was "not insecure". This referred to the zone, not the response.)
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.
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.
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.
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 dnssec-keygen(8) and dnssec-settime(8) 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.
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
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.
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.
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.
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.
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.
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.
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).
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.
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.
BIND 9.7.0 introduces support for RFC 5011, dynamic trust anchor management. Using 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.
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 the section called “managed-keys Statement Definition and Usage”.
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.
Older versions of BIND 9 did not have this precaution. Exercise caution if using key revocation on keys that were generated by previous releases, or if using keys stored in multiple directories or on multiple machines.
It is expected that a future release of BIND 9 will address this problem in a different way, by storing revoked keys with their original unrevoked key ID's.
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.
BIND 9 is known to work with two HSMs: The Sun SCA 6000 cryptographic acceleration board, tested under Solaris x86, and the AEP Keyper network-attached key storage device, tested with Debian Linux, Solaris x86 and Windows Server 2003.
See the HSM vendor documentation for information about installing, initializing, testing and troubleshooting the HSM.
BIND 9 uses OpenSSL for cryptography, but stock OpenSSL does not yet fully support PKCS #11. However, a PKCS #11 engine for OpenSSL is available from the OpenSolaris project. It has been modified by ISC to work with with BIND 9, and to provide new features such as PIN management and key by reference.
The patched OpenSSL depends on a "PKCS #11 provider". This is a shared library object, providing a low-level PKCS #11 interface to the HSM hardware. It is dynamically loaded by OpenSSL at runtime. The PKCS #11 provider comes from the HSM vendor, and is specific to the HSM to be controlled.
There are two "flavors" of PKCS #11 support provided by the patched OpenSSL, one of which must be chosen at configuration time. The correct choice depends on the HSM hardware:
Use 'crypto-accelerator' with HSMs that have hardware cryptographic acceleration features, such as the SCA 6000 board. This causes OpenSSL to run all supported cryptographic operations in the HSM.
Use 'sign-only' with HSMs that are designed to function primarily as secure key storage devices, but lack hardware acceleration. These devices are highly secure, but are not necessarily any faster at cryptography than the system CPU — often, they are slower. It is therefore most efficient to use them only for those cryptographic functions that require access to the secured private key, such as zone signing, and to use the system CPU for all other computationally-intensive operations. The AEP Keyper is an example of such a device.
The modified OpenSSL code is included in the BIND 9 release, in the form of a context diff against the latest versions of OpenSSL. OpenSSL 0.9.8, 1.0.0, 1.0.1 and 1.0.2 are supported; there are separate diffs for each version. In the examples to follow, we use OpenSSL 0.9.8, but the same methods work with OpenSSL 1.0.0 through 1.0.2.
Before building BIND 9 with PKCS #11 support, it will be necessary to build OpenSSL with this patch in place and inform it of the path to the HSM-specific PKCS #11 provider library.
Obtain OpenSSL 0.9.8s:
$ wget http://www.openssl.org/source/openssl-0.9.8s.tar.gz
Extract the tarball:
$ tar zxf openssl-0.9.8s.tar.gz
Apply the patch from the BIND 9 release:
$ patch -p1 -d openssl-0.9.8s \
< bind9/bin/pkcs11/openssl-0.9.8s-patch
When building OpenSSL, place it in a non-standard location so that it does not interfere with OpenSSL libraries elsewhere on the system. In the following examples, we choose to install into "/opt/pkcs11/usr". We will use this location when we configure BIND 9.
The AEP Keyper is a highly secure key storage device, but does not provide hardware cryptographic acceleration. It can carry out cryptographic operations, but it is probably slower than your system's CPU. Therefore, we choose the 'sign-only' flavor when building OpenSSL.
The Keyper-specific PKCS #11 provider library is delivered with the Keyper software. In this example, we place it /opt/pkcs11/usr/lib:
$ cp pkcs11.GCC4.0.2.so.4.05 /opt/pkcs11/usr/lib/libpkcs11.so
The Keyper library requires threads, so we must specify -pthread.
$cd openssl-0.9.8s$./Configure linux-x86_64 -pthread \ --pk11-libname=/opt/pkcs11/usr/lib/libpkcs11.so \ --pk11-flavor=sign-only \ --prefix=/opt/pkcs11/usr
After configuring, run "make" and "make test". If "make test" fails with "pthread_atfork() not found", you forgot to add the -pthread above.
The SCA-6000 PKCS #11 provider is installed as a system library, libpkcs11. It is a true crypto accelerator, up to 4 times faster than any CPU, so the flavor shall be 'crypto-accelerator'.
In this example, we are building on Solaris x86 on an AMD64 system.
$cd openssl-0.9.8s$./Configure solaris64-x86_64-cc \ --pk11-libname=/usr/lib/64/libpkcs11.so \ --pk11-flavor=crypto-accelerator \ --prefix=/opt/pkcs11/usr
(For a 32-bit build, use "solaris-x86-cc" and /usr/lib/libpkcs11.so.)
After configuring, run make and make test.
SoftHSM is a software library provided by the OpenDNSSEC project (http://www.opendnssec.org) which provides a PKCS#11 interface to a virtual HSM, implemented in the form of encrypted data on the local filesystem. It uses the Botan library for encryption and SQLite3 for data storage. Though less secure than a true HSM, it can provide more secure key storage than traditional key files, and can allow you to experiment with PKCS#11 when an HSM is not available.
The SoftHSM cryptographic store must be installed and initialized before using it with OpenSSL, and the SOFTHSM_CONF environment variable must always point to the SoftHSM configuration file:
$cd softhsm-1.3.0$configure --prefix=/opt/pkcs11/usr$make$make install$export SOFTHSM_CONF=/opt/pkcs11/softhsm.conf$echo "0:/opt/pkcs11/softhsm.db" > $SOFTHSM_CONF$/opt/pkcs11/usr/bin/softhsm --init-token 0 --slot 0 --label softhsm
SoftHSM can perform all cryptographic operations, but since it only uses your system CPU, there is no need to use it for anything but signing. Therefore, we choose the 'sign-only' flavor when building OpenSSL.
$cd openssl-0.9.8s$./Configure linux-x86_64 -pthread \ --pk11-libname=/opt/pkcs11/usr/lib/libpkcs11.so \ --pk11-flavor=sign-only \ --prefix=/opt/pkcs11/usr
After configuring, run "make" and "make test".
Once you have built OpenSSL, run "apps/openssl engine pkcs11" to confirm that PKCS #11 support was compiled in correctly. The output should be one of the following lines, depending on the flavor selected:
(pkcs11) PKCS #11 engine support (sign only)
Or:
(pkcs11) PKCS #11 engine support (crypto accelerator)
Next, run
"apps/openssl engine pkcs11 -t". This will
attempt to initialize the PKCS #11 engine. If it is able to
do so successfully, it will report
“[ available ]”.
If the output is correct, run
"make install" which will install the
modified OpenSSL suite to
/opt/pkcs11/usr.
When building BIND 9, the location of the custom-built OpenSSL library must be specified via configure.
To link with the PKCS #11 provider, threads must be enabled in the BIND 9 build.
$cd ../bind9$./configure --enable-threads \ --with-openssl=/opt/pkcs11/usr \ --with-pkcs11=/opt/pkcs11/usr/lib/libpkcs11.so
To link with the PKCS #11 provider, threads must be enabled in the BIND 9 build.
$cd ../bind9$./configure CC="cc -xarch=amd64" --enable-threads \ --with-openssl=/opt/pkcs11/usr \ --with-pkcs11=/usr/lib/64/libpkcs11.so
(For a 32-bit build, omit CC="cc -xarch=amd64".)
If configure complains about OpenSSL not working, you may have a 32/64-bit architecture mismatch. Or, you may have incorrectly specified the path to OpenSSL (it should be the same as the --prefix argument to the OpenSSL Configure).
$cd ../bind9$./configure --enable-threads \ --with-openssl=/opt/pkcs11/usr \ --with-pkcs11=/opt/pkcs11/usr/lib/libpkcs11.so
After configuring, run "make", "make test" and "make install".
(Note: If "make test" fails in the "pkcs11" system test, you may have forgotten to set the SOFTHSM_CONF environment variable.)
BIND 9 includes a minimal set of tools to operate the HSM, including pkcs11-keygen to generate a new key pair within the HSM, pkcs11-list to list objects currently available, and pkcs11-destroy to remove objects.
In UNIX/Linux builds, these tools are built only if BIND 9 is configured with the --with-pkcs11 option. (NOTE: If --with-pkcs11 is set to "yes", rather than to the path of the PKCS #11 provider, then the tools will be built but the provider will be left undefined. Use the -m option or the PKCS11_PROVIDER environment variable to specify the path to the provider.)
First, we must set up the runtime environment so the OpenSSL and PKCS #11 libraries can be loaded:
$ export LD_LIBRARY_PATH=/opt/pkcs11/usr/lib:${LD_LIBRARY_PATH}
When operating an AEP Keyper, it is also necessary to
specify the location of the "machine" file, which stores
information about the Keyper for use by PKCS #11 provider
library. If the machine file is in
/opt/Keyper/PKCS11Provider/machine,
use:
$ export KEYPER_LIBRARY_PATH=/opt/Keyper/PKCS11Provider
These environment variables must be set whenever running any tool that uses the HSM, including pkcs11-keygen, pkcs11-list, pkcs11-destroy, dnssec-keyfromlabel, dnssec-signzone, dnssec-keygen(which will use the HSM for random number generation), and named.
We can now create and use keys in the HSM. In this case, we will create a 2048 bit key and give it the label "sample-ksk":
$ pkcs11-keygen -b 2048 -l sample-ksk
To confirm that the key exists:
$ pkcs11-list
Enter PIN:
object[0]: handle 2147483658 class 3 label[8] 'sample-ksk' id[0]
object[1]: handle 2147483657 class 2 label[8] 'sample-ksk' id[0]
Before using this key to sign a zone, we must create a pair of BIND 9 key files. The "dnssec-keyfromlabel" utility does this. In this case, we will be using the HSM key "sample-ksk" as the key-signing key for "example.net":
$ dnssec-keyfromlabel -l sample-ksk -f KSK example.net
The resulting K*.key and K*.private files can now be used to sign the zone. Unlike normal K* files, which contain both public and private key data, these files will contain only the public key data, plus an identifier for the private key which remains stored within the HSM. The HSM handles signing with the private key.
If you wish to generate a second key in the HSM for use as a zone-signing key, follow the same procedure above, using a different keylabel, a smaller key size, and omitting "-f KSK" from the dnssec-keyfromlabel arguments:
$pkcs11-keygen -b 1024 -l sample-zsk$dnssec-keyfromlabel -l sample-zsk example.net
Alternatively, you may prefer to generate a conventional on-disk key, using dnssec-keygen:
$ dnssec-keygen example.net
This provides less security than an HSM key, but since HSMs can be slow or cumbersome to use for security reasons, it may be more efficient to reserve HSM keys for use in the less frequent key-signing operation. The zone-signing key can be rolled more frequently, if you wish, to compensate for a reduction in key security.
Now you can sign the zone. (Note: If not using the -S
option to
dnssec-signzone, it will be necessary to add
the contents of both
K*.key files to the zone master file before
signing it.)
$ dnssec-signzone -S example.net
Enter PIN:
Verifying the zone using the following algorithms:
NSEC3RSASHA1.
Zone signing complete:
Algorithm: NSEC3RSASHA1: ZSKs: 1, KSKs: 1 active, 0 revoked, 0 stand-by
example.net.signed
The OpenSSL engine can be specified in named and all of the BIND dnssec-* tools by using the "-E <engine>" command line option. If BIND 9 is built with the --with-pkcs11 option, this option defaults to "pkcs11". Specifying the engine will generally not be necessary unless for some reason you wish to use a different OpenSSL engine.
If you wish to disable use of the "pkcs11" engine — for troubleshooting purposes, or because the HSM is unavailable — set the engine to the empty string. For example:
$ dnssec-signzone -E '' -S example.net
This causes dnssec-signzone to run as if it were compiled without the --with-pkcs11 option.
If you want
named to dynamically re-sign zones using HSM
keys, and/or to to sign new records inserted via nsupdate, then
named must have access to the HSM PIN. This can be accomplished
by placing the PIN into the openssl.cnf file (in the above
examples,
/opt/pkcs11/usr/ssl/openssl.cnf).
The location of the openssl.cnf file can be overridden by setting the OPENSSL_CONF environment variable before running named.
Sample openssl.cnf:
openssl_conf = openssl_def
[ openssl_def ]
engines = engine_section
[ engine_section ]
pkcs11 = pkcs11_section
[ pkcs11_section ]
PIN = <PLACE PIN HERE>
This will also allow the dnssec-* tools to access the HSM without PIN entry. (The pkcs11-* tools access the HSM directly, not via OpenSSL, so a PIN will still be required to use them.)
Placing the HSM's PIN in a text file in this manner may reduce the security advantage of using an HSM. Be sure this is what you want to do before configuring OpenSSL in this way.
BIND 9 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, BIND 9 supports only AAAA records. RFC 3363 deprecated the use of A6 records, and client-side support for A6 records was accordingly removed from BIND 9. However, authoritative BIND 9 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, BIND 9 supports the traditional "nibble" format used in the ip6.arpa domain, as well as the older, deprecated ip6.int domain. Older versions of BIND 9 supported the "binary label" (also known as "bitstring") format, but support of binary labels has been completely removed per RFC 3363. Many applications in BIND 9 do not understand the binary label format at all any more, and will return an error if given. In particular, an authoritative BIND 9 name server will not load a zone file containing binary labels.
For an overview of the format and structure of IPv6 addresses, see the section called “IPv6 addresses (AAAA)”.
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:192.168.42.1 as
the address.
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 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
host.example.com. )
BIND 9.9.10rc3 (Extended Support Version)