KDC(8)

NAME
kdc - Kerberos 5 server

SYNOPSIS
kdc [-c file - -config-file=file] [-p | - -no-require-preauth] [- -max-request=size] [-H | - -enable-http] [-r string - -v4-realm=string] [-P portspec - -ports=portspec] [- -detach] [- -disable-des] [- -addresses=list of addresses]

DESCRIPTION
kdc serves requests for tickets. When it starts, it first checks the flags passed, any options that are not specified with a command line flag are taken from a config file, or from a default compiled-in value.

Options supported:

-c file, - -config-file=file
    Specifies the location of the config file, the default is /var/lib/heimdal/kdc.conf. This is the only value that can't be specified in the config file.

-p, - -no-require-preauth
    Turn off the requirement for pre-autentication in the initial AS-REQ for all principals. The use of pre-authentication makes it more difficult to do offline password attacks. You might want to turn it off if you have clients that don't support pre-authentication. Since the version 4 protocol doesn't support any pre-authentication, serving version 4 clients is just about the same as not requiring pre-athentication. The default is to require pre-authentication. Adding the require-preauth per principal is a more flexible way of handling this.

- -max-request=size
    Gives an upper limit on the size of the requests that the kdc is willing to handle.

-H, - -enable-http
    Makes the kdc listen on port 80 and handle requests encapsulated in HTTP.

-r string, - -v4-realm=string
    What realm this server should act as when dealing with version 4 requests. The database can contain any number of realms, but since the version 4 protocol doesn't contain a realm for the server, it must be explicitly specified. The default is whatever is returned by krb_get_lrealm(). This option is only available if the KDC has been compiled with version 4 support.

-P portspec, - -ports=portspec
    Specifies the set of ports the KDC should listen on. It is given as a white-space separated list of services or port numbers.

- -addresses=list of addresses
    The list of addresses to listen for requests on. By default, the kdc will listen on all the locally configured addresses. If only a subset is desired, or the automatic detection fails, this option might be used.

- -detach
    detach from pty and run as a daemon.

- -disable-des
    disable all des encryption types, makes the kdc not use them.

All activities are logged to one or more destinations, see krb5.conf(5), and krb5_openlog(3). The entity used for logging is kdc.

CONFIGURATION FILE
The configuration file has the same syntax as krb5.conf(5), but will be read before /etc/krb5.conf, so it may override settings found there. Options specific to the KDC only are found in the “[kdc]” section. All the command-line options can preferably be added in the configuration file. The only difference is the pre-authentication flag, which has to be specified as:

    require-preauth = no

(in fact you can specify the option as - -require-preauth=no).

And there are some configuration options which do not have command-line equivalents:

enable-digest = boolean
    turn on support for digest processing in the KDC. The default is FALSE.

check-ticket-addresses = boolean
    Check the addresses in the ticket when processing TGS requests. The default is TRUE.

allow-null-ticket-addresses = boolean
    Permit tickets with no addresses. This option is only relevant when check-ticket-addresses is TRUE.

allow-anonymous = boolean
    Permit anonymous tickets with no addresses.

historical_anon_realm = boolean
    Enables pre-7.0 non-RFC-comformant KDC behavior. With this option set to true the client realm in anonymous pkinit AS replies will be the requested realm, rather than the RFC-conformant WELLKNOWN:ANONYMOUS realm. This can have a security impact on servers that expect to grant access to anonymous-but-authenticated to the KDC users of the realm in question: they would also grant access to unauthenticated anonymous users. As such, it is not recommend to set this option to true.

max-kdc-datagram-reply-length = number
    Maximum packet size the UDP rely that the KDC will transmit, instead the KDC sends back a reply telling the client to use TCP instead.

transited-policy = always-check allow-per-principal | always-honour-request
    This controls how KDC requests with the disable-transited-check flag are handled. It can be one of:

    always-check
        Always check transited encoding, this is the default.

    allow-per-principal
        Currently this is identical to always-check. In a future release, it will be possible to mark a principal as able to handle unchecked requests.

    always-honour-request
        Always do what the client asked. In a future release, it will be possible to force a check per principal.

encode_as_rep_as_tgs_rep = boolean
    Encode AS-Rep as TGS-Rep to be bug-compatible with old DCE code. The Heimdal clients allow both.

kdc_warn_pwexpire = time
    How long before password/principal expiration the KDC should start sending out warning messages.

The configuration file is only read when the kdc is started. If changes made to the configuration file are to take effect, the kdc needs to be restarted.

An example of a config file:

    [kdc]
    	require-preauth = no
    	v4-realm = FOO.SE

BUGS
If the machine running the KDC has new addresses added to it, the KDC will have to be restarted to listen to them. The reason it doesn't just listen to wildcarded (like INADDR_ANY) addresses, is that the replies has to come from the same address they were sent to, and most OS:es doesn't pass this information to the application. If your normal mode of operation require that you add and remove addresses, the best option is probably to listen to a wildcarded TCP socket, and make sure your clients use TCP to connect. For instance, this will listen to IPv4 TCP port 88 only:

    kdc --addresses=0.0.0.0 --ports="88/tcp"

There should be a way to specify protocol, port, and address triplets, not just addresses and protocol, port tuples.

SEE ALSO
kinit(1), krb5.conf(5)