• Debian
  • • • • Install packages:
        • Load kerberos LDAP schema:
        • Create Index on krbPrincipalName:
        • Create principals kadmin and kdc:

Debian

The guide I followed was https://wiki.debian.org/LDAP/OpenLDAPSetup#Kerberos which while it worked required some minor tweaks. I obtained edit privileges for the Debian Wiki and updated the guide with the fixes that I found. I however have a Synology NAS and that can run an LDAP Server. So this guide differs from the upstream Debian Guide.

Assumption is that you have installed the LDAP Server package on your NAS and gone through initial configuration steps, so it has a domain, there is a DN you can bind as and so forth. It is also assumed you have a Debian system (12.5 or later, though this guide should work with 11.x and likely 10.x as well) that will become your KDC and KAdmin server.

Recommendation is that you create actual .ldif files rather than use here-documents as used in this guide. It is far easier to make adjustments to things if you have a file to edit rather than having to type it all out again or paste it and then have to try and make edits to it without making mistakes.

The guide is for illustration. Expectation is that you do not follow it verbatim but adapt it to your needs.

Install packages:

The packages you need are krb5-kdc-ldap, krb5-admin-server for the actual KDC and schema2ldif  plus slapd for adding the schema and slappasswd. They are to be installed on your designated Debian host.

$ sudo apt install krb5-kdc-ldap krb5-admin-server schema2ldif

Load kerberos LDAP schema:

Now you need to load the kerberos schema into the LDAP server on the Synology. And here you need to use the cn=config DN.

$ zcat /usr/share/doc/krb5-kdc-ldap/kerberos.openldap.ldif.gz | ldapadd -H ldaps://nas.example.com/ -D cn=config -W
Enter LDAP Password:
adding new entry "cn=kerberos,cn=schema,cn=config"
$

Create Index on krbPrincipalName:

Having an index on the krbPrincipalName improves performance and also suppresses some log messages if slapd is configured to log more than default for the database(s) where you intend to store Kerberos data. As this is OpenLDAP on the Synology, it does not use mdb format, it uses bdb. If you install slapd on Debian, it uses mdb format. It is different database format, but the principle is the same. Again, as you are modifying config, the DN is cn=config. Interestingly, it is still the main password you set for the Synology LDAP server.

$ ldapmodify -H ldaps://nas.example.com/ -D cn=config -W <<EOF
dn: olcDatabase={1}bdb,cn=config
add: olcDbIndex
olcDbIndex: krbPrincipalName eq,pres,sub
EOF
Enter LDAP Password:
modifying entry "olcDatabase={1}bdb,cn=config"
$

Create principals kadmin and kdc:

Next, you create and configure two entries which will be used by the Kerberos servers to connect to OpenLDAP. As you will not run the Kerberos KDC and Admin Server on the same host as OpenLDAP, these steps are required. In order to keep things nicely separated, everything will be created under a separate organizationalUnit. I diverge from the official Debian guide here as I do not agree with the DN they use. I also had to make changes to the DNs of kdc and kadmin due to pwdPolicy applied by Synology to their LDAP server. The official guide will have you use placeholder passwords and that does not work with the Synology LDAP server. You need to generate them upfront with slappasswd -h {SSHA}.

$ ldapadd -H ldap://nas.example.com/ -D uid=root,cn=users,dc=example,dc=com -W <<EOF
dn: ou=kerberos,dc=example,dc=com
objectClass: organizationalUnit
objectClass: top
ou: kerberos

dn: cn=kdc,ou=kerberos,dc=example,dc=com
cn: kdc
sn: kdc
objectClass: person
objectClass: pwdPolicy
pwdAttribute: userPassword
pwdMinLength: 8
pwdCheckQuality: 2
pwdPolicySubentry: cn=kdc,ou=kerberos,dc=example,dc=com
userPassword: {SSHA}<password-hash>
description: Kerberos KDC Account

dn: cn=kadmin,ou=kerberos,dc=example,dc=com
cn: kadmin
sn: kadmin
objectClass: person
objectClass: pwdPolicy
pwdAttribute: userPassword
pwdMinLength: 8
pwdCheckQuality: 2
pwdPolicySubentry: cn=kadmin,ou=kerberos,dc=example,dc=com
userPassword: {SSHA}<password-hash>
description: Kerberos KDC Account
EOF
Enter LDAP Password:

adding new entry "ou=kerberos,dc=example,dc=com"

adding new entry "cn=kdc,ou=kerberos,dc=example,dc=com"

adding new entry "cn=kadmin,ou=kerberos,dc=example,dc=com"

Synology LDAP server did not like adding users with placeholder passwords, because Synology puts in place password policies. Hence changing this to a cn instead of a uid.  It seems to have worked out fine as my KDC is fully functioning.