credns.conf

NAME
SYNOPSIS
DESCRIPTION
EXAMPLE
FILE FORMAT
CREDNS CONFIGURATION FOR BIND9 HACKERS
FILES
SEE ALSO
AUTHORS
BUGS

NAME

credns.conf − Credns configuration file

SYNOPSIS

credns.conf

DESCRIPTION

Credns.conf is used to configure credns(8). The file format has attributes and values. Some attributes have attributes inside them. The notation is: attribute: value.

Comments start with # and last to the end of line. Empty lines are ignored as is whitespace at the beginning of a line.

Credns.conf specifies options for the credns server, zone files, primaries and secondaries.

EXAMPLE

An example of a short credns.conf file is below.

# Example.com credns.conf file
# This is a comment.
server:

database: "/var/db/credns/credns.db"
username: credns
logfile: "/var/log/credns.log"
pidfile: "/var/run/credns.pid"
difffile: "/var/db/credns/ixfr.db"
xfrdfile: "/var/db/credns/xfrd.state"
ip-address: 10.10.0.1

zone:

name: example.com

# Accept notifies and xfr from the hidden master
allow-notify: 10.0.0.1 NOKEY
request-xfr: 10.0.0.1 NOKEY

verifier: ldns-verify-zone -V2

# Notify and xfr to the public slave
notify: 10.20.0.1 NOKEY
provide-xfr: 10.20.0.1 NOKEY

FILE FORMAT

There must be whitespace between keywords. Attribute keywords end with a colon ’:’. An attribute is followed by its containing attributes, or a value.

At the top level only server: or zone: or key: are allowed. These are followed by their attributes or the start of a new server: or zone: or key: clause. The zone: attribute is followed by zone options. The server: attribute is followed by global options for the credns server. A key: attribute is used to define keys for authentication.

Files can be included using the include: directive. It can appear anywhere, and takes a single filename as an argument. Processing continues as if the text from the included file was copied into the config file at that point.

Server Options
The global options (if not overridden from the credns commandline) are taken from the server: clause. There may only be one server: clause.
ip−address:
<ip4 or ip6>@port

Credns will bind to the listed ip−address. Can be give multiple times to bind multiple ip−addresses. Optionally, a port number can be given. If none are given dnssext listens to the wildcard interface. Same as commandline option −a.

debug−mode: <yes or no>

Turns on debugging mode for credns, does not fork a daemon process. Default is no. Same as commandline option −d.

ip4−only: <yes or no>

If yes, credns only listens to IPv4 connections. Same as commandline option −4.

ip6−only: <yes or no>

If yes, credns only listens to IPv6 connections. Same as commandline option −6.

database: <filename>

By default /var/db/credns/credns.db is used. The specified file is used to store the compiled zone information. Same as commandline option −f.

identity: <string>

Returns the specified identity when asked for CH TXT ID.SERVER. Default is the name as returned by gethostname(3). Same as commandline option −i.

nsid: <string>

Add the specified nsid to the EDNS section of the answer when queried with an NSID EDNS enabled packet. Same as commandline option −I.

logfile: <filename>

Log messages to the logfile. The default is to log to stderr and syslog (with facility LOG_DAEMON). Same as commandline option −l.

server−count: <number>

Start this many credns servers. Default is 1. Same as commandline option −N.

tcp−count: <number>

The maximum number of concurrent, active TCP connections by each server. Default is 10. This option should have a value below 1000. Same as commandline option −n.

tcp−query−count: <number>

The maximum number of queries served on a single TCP connection. Default is 0, meaning there is no maximum.

tcp−timeout: <number>

Overrides the default TCP timeout. This also affects zone transfers over TCP.

ipv4−edns−size: <number>

Preferred EDNS buffer size for IPv4.

ipv6−edns−size: <number>

Preferred EDNS buffer size for IPv6.

pidfile: <filename>

Use the pid file instead of the platform specific default, usually /var/run/credns.pid. Same as commandline option −P.

port: <number>

Answer queries on the specified port. Default is 53. Same as commandline option −p.

statistics: <number>

If not present no statistics are dumped. Statistics are produced every number seconds. Same as commandline option −s.

zone-stats-file: <filename>

If per zone statistics is enabled, file to dump the statistics.

chroot: <directory>

Credns will chroot on startup to the specified directory. Same as commandline option −t.

username: <username>

After binding the socket, drop user privileges and assume the username. Can be username, id or id.gid. Same as commandline option −u.

zonesdir: <directory>

Change the working directory to the specified directory before accessing zone files. Same as commandline option −d for zonec(8). Also credns(8) will access files (pid file, database file, log file) relative to this directory. Set the value to "" (the empty string) to disable the change of working directory.

difffile: <filename>

When credns receives IXFR updates it will store them in this file. This file contains the differences between the database file and the latest zone version. Default is /var/db/credns/ixfr.db.

xfrdfile: <filename>

The soa timeout and zone transfer daemon in credns will save its state to this file. State is read back after a restart. The state file can be deleted without too much harm, but timestamps of zones will be gone. For more details see the section on zone expiry behavior of credns. Default is /var/db/credns/xfrd.state.

xfrd−reload−timeout: <number>

If this value is −1, xfrd will not trigger a reload after a zone transfer. If positive xfrd will trigger a reload after a zone transfer, then it will wait for the number of seconds before it will trigger a new reload. Setting this value throttles the reloads to once per the number of seconds. The default is 10 seconds.

verbosity: <level>

This value specifies the verbosity level for (non−debug) logging. Default is 0. 1 gives more information about incoming notifies and zone transfers. 2 lists soft warnings that are encountered.

hide−version: <yes or no>

Prevent credns from replying with the version string on CHAOS class queries.

verifier−count: <number>

Number of verifiers that may run simultaneously. 0 means that no verifiers should be run at all, which will prevent all zones − with a verifier: attribute in their zone: clause − from being updated by IXFR or AXFR. The default is 1.

verifier−feed-zone: <yes or no>

Feed a by IXFR or AXFR updated zone to the standard input (stdin) of a verifier. The default is "yes". This attribute may be overloaded per zone.

verify−ip−address: <ip4 or ip6>@port

Serve the zone to the verifier on the listed ip-address. Can be given multiple times to bind multiple ip-addresses. Optionally, a port number can be given. The default is to have no verify−ip−address: and to not serve the zone to a verifier.

verify-port: <number>

Serve the zone to the verifier on this port. Note that the zone will not be served to a verifier when no verify−ip−address: attribute is given. The default is port 5347.

verifier−timeout: <number>

The maximum number of seconds a verifier should take for assessing one zone. If the verifier takes longer, it will be terminated and the update to the zone will be discarded. The default is 0 seconds which means the verifier may take as long as it needs. This attribute may be overloaded per zone.

Zone Options
For every zone the options need to be specified in one zone: clause. The access control list elements can be given multiple times to add multiple servers. These elements need to be added explicitly.
name:
<string>

The name of the zone. This is the domain name of the apex of the zone. May end with a ’.’ (in FQDN notation). For example "example.com", "sub.example.net.". This attribute must be present in each zone.

zonefile: <filename>

The file containing the zone information. This file is used by zonec(8). This attribute must be present in each zone.

allow−notify: <ip−spec> <key−name | NOKEY | BLOCKED>

Access control list. The listed (primary) address is allowed to send notifies to this (secondary) server. Notifies from unlisted or specifically BLOCKED addresses are discarded. If NOKEY is given no TSIG signature is required.

The ip−spec is either a plain IP address (IPv4 or IPv6), or can be a subnet of the form 1.2.3.4/24, or masked like 1.2.3.4&255.255.255.0 or a range of the form 1.2.3.4−1.2.3.25. A port number can be added using a suffix of @number, for example 1.2.3.4@5300 or 1.2.3.4/24@5300 for port 5300. Note the ip−spec ranges do not use spaces around the /, &, @ and − symbols.

request−xfr: AXFR|UDP <ip−address> <key−name | NOKEY>

Access control list. The listed address (the master) is queried for AXFR/IXFR on update. A port number can be added using a suffix of @number, for example 1.2.3.4@5300. The specified key is used during AXFR/IXFR.

If the AXFR option is given, the server will not be contacted with IXFR queries but only AXFR requests will be made to the server. This allows an credns secondary to have a master server that runs NSD. If the AXFR option is left out then both IXFR and AXFR requests are made to the master server.

If the UDP option is given, the secondary will use UDP to transmit the IXFR requests. You should deploy TSIG when allowing UDP transport, to authenticate notifies and zone transfers. Otherwise, credns is more vulnerable for Kaminsky-style attacks. If the UDP option is left out then IXFR will be transmitted using TCP.

allow−axfr−fallback: <yes or no>

This option should be accompanied by request-xfr. It (dis)allows credns (as secondary) to fallback to AXFR if the primary name server does not support IXFR. Default is yes.

notify: <ip−address> <key−name | NOKEY>

Access control list. The listed address (a secondary) is notified of updates to this zone. A port number can be added using a suffix of @number, for example 1.2.3.4@5300. The specified key is used to sign the notify. Only on secondary configurations will credns be able to detect zone updates (as it gets notified itself, or refreshes after a time).

notify−retry: <number>

This option should be accompanied by notify. It sets the number of retries when sending notifies.

provide−xfr: <ip−spec> <key−name | NOKEY | BLOCKED>

Access control list. The listed address (a secondary) is allowed to request AXFR from this server. Zone data will be provided to the address. The specified key is used during AXFR. For unlisted or BLOCKED addresses no data is provided, requests are discarded.

The ip−spec is either a plain IP address (IPv4 or IPv6), or can be a subnet of the form 1.2.3.4/24, or masked like 1.2.3.4&255.255.255.0 or a range of the form 1.2.3.4−1.2.3.25. A port number can be added using a suffix of @number, for example 1.2.3.4@5300 or 1.2.3.4/24@5300 for port 5300. Note the ip−spec ranges do not use spaces around the /, &, @ and − symbols.

outgoing−interface: <ip−address>

Access control list. The listed address is used to request AXFR|IXFR (in case of a secondary) or used to send notifies (in case of a primary).

The ip−address is a plain IP address (IPv4 or IPv6). A port number can be added using a suffix of @number, for example 1.2.3.4@5300.

verifier: <program with arguments>

When an update is received for the zone (by IXFR or AXFR) this program will be run to asses the zone with the update. When the program exits with a status code of 0, the zone is considered good and will be served. Any other status code will designate the zone bad and the received update will be discarded. Credns will then continue to serve the zone but without the update.

The following environment variables are available for verifiers:

VERIFY_ZONE

The domain name of the zone to be verified.

VERIFY_ZONE_ON_STDIN

When the zone can be read from the standard input, this variable will be set to "yes", otherwise it will be empty.

VERIFY_IP_ADDRESSES

A list of <ip-address>@<port> combinations on which the zones to be assessed will be served.

VERIFY_IP_ADDRESS

The first address on which the zones to be assessed will be served. If IPv6 is available an IPv6 address will be prefered over IPv4.

VERIFY_PORT

the port number for VERIFY_IP_ADDRESS

VERIFY_IPV6_ADDRESS

The first IPv6 address on which the zones to be assessed will be served.

VERIFY_IPV6_PORT

The port number for VERIFY_IPV6_ADDRESS.

VERIFY_IPV4_ADDRESS

The first IPv4 address on which the zones to be assessed will be served.

VERIFY_IPV4_PORT

The port number for VERIFY_IPV4_ADDRESS.

verifier−feed-zone: <yes, no or inherit>

Feed the updated zone on the standard input (stdin) of the verifier. The default is "inherit", which means that the value of the verifier−feed−zone: attribute from the server: clause will be used.

verifier−timeout: <number or inherit>

The maximum number of seconds a verifier should take for assessing one zone. If the verifier takes longer, it will be terminated and the update to the zone will be discarded. The default is "inherit", which means that the value of the verifier−timeout: attribute from the server: clause will be used.

Key Declarations
The key: clause establishes a key for use in access control lists. It has the following attributes.
name:
<string>

The key name. Used to refer to this key in the access control list.

algorithm: <string>

Authentication algorithm for this key.

secret: <base64 blob>

The base64 encoded shared secret. It is possible to put the secret: declaration (and base64 blob) into a different file, and then to include: that file. In this way the key secret and the rest of the configuration file, which may have different security policies, can be split apart.

CREDNS CONFIGURATION FOR BIND9 HACKERS

BIND9 is a name server implementation with its own configuration file format, named.conf(5). BIND9 types zones as ’Master’ or ’Slave’.

Slave zones
For a slave zone, the master servers are listed. The master servers are queried for zone data, and are listened to for update notifications. In credns these two properties need to be configured separately, by listing the master address in allow−notify and request−xfr statements.

In BIND9 you only need to provide allow−notify elements for any extra sources of notifications (i.e. the operators), credns needs to have allow−notify for both masters and operators. BIND9 allows additional transfer sources, in credns you list those as request−xfr.

Here is an example of a slave zone in BIND9 syntax.

# Config file for example.org options {

dnssec−enable yes;

};

key tsig.example.org. {

algorithm hmac−md5;
secret "aaaaaabbbbbbccccccdddddd";

};

server 162.0.4.49 {

keys { tsig.example.org. ; };

};

zone "example.org" {

type slave;
file "secondary/example.org.signed";
masters { 162.0.4.49; };

};

For credns, DNSSEC is enabled automatically for zones that are signed. The dnssec−enable statement in the options clause is not needed. In credns keys are associated with an IP address in the access control list statement, therefore the server{} statement is not needed. Below is the same example in an credns config file.

# Config file for example.org
key:

name: tsig.example.org.
algorithm: hmac−md5
secret: "aaaaaabbbbbbccccccdddddd"

zone:

name: "example.org"
zonefile: "secondary/example.org.signed"
# the master is allowed to notify and will provide zone data.
allow−notify: 162.0.4.49 NOKEY
request−xfr: 162.0.4.49 tsig.example.org.

Notice that the master is listed twice, once to allow it to send notifies to this slave server and once to tell the slave server where to look for updates zone data. More allow−notify and request−xfr lines can be added to specify more masters.

It is possible to specify extra allow−notify lines for addresses that are also allowed to send notifications to this slave server.

Providing transfer
For a master zone in BIND9, the slave servers are listed. These slave servers are sent notifications of updated and are allowed to request transfer of the zone data. In credns these two properties need to be configured separately.

Here is an example of a master zone in BIND9 syntax.

zone "example.nl" {

type master;
file "example.nl";

};

In credns syntax this becomes:

zone:

name: "example.nl"
zonefile: "example.nl"
# allow anybody to request xfr.
provide−xfr: 0.0.0.0/0 NOKEY
provide−xfr: ::0/0 NOKEY

# to list a slave server you would in general give
# provide−xfr: 1.2.3.4 tsig−key.name.
# notify: 1.2.3.4 NOKEY

Other
Credns is an authoritative transfer only DNS. This means that it is meant to request and provide transfer and notifies to other authoritative nameservers. BIND9 can function as an authoritative DNS server, the configuration options for that are compared with those for credns in this section. However, BIND9 can also function as a resolver or cache. The configuration options that BIND9 has for the resolver or caching thus have no equivalents for credns.

FILES

/var/db/credns/credns.db

default credns database

/etc/credns/credns.conf

default credns configuration file

SEE ALSO

credns(8), crednsc(8), credns−checkconf(8), credns-notify(8), credns-patch(8), credns-xfer(8)

AUTHORS

Credns was written by NLnet Labs.

NSD was written by NLnet Labs and RIPE NCC joint team. Please see CREDITS file in the distribution for further details.

BUGS

credns.conf is parsed by a primitive parser, error messages may not be to the point.


←Credns

Wed Sep 25 2013

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