Verifying and Creating a DC DNS Record

Introduction

Samba currently does not create two important DNS records when you join a domain controller (DC) to a Samba AD. These records are required for the directory replication to work properly.

For more details, see Bug #10928.

Domain Controller A Record

To verify that the A record for domain controller (DC) "DC2" using the IP address "10.99.0.2" is created in the "samdom.example.com" DNS zone, run on a domain member:

# host -t A DC2.samdom.example.com.
DC2.samdom.example.com has address 10.99.0.2

If the record is missing, the following error is displayed:

# host -t A DC2.samdom.example.com.
Host DC2.samdom.example.com. not found: 3(NXDOMAIN)

To manually add the A record for "DC2" to the DNS server running on "DC1", run:

# samba-tool dns add DC1 samdom.example.com DC2 A 10.99.0.2 -Uadministrator
Password for [SAMDOM\administrator]: 
Record added successfully

The directory replication automatically distributes the new record to all DCs.

The objectGUID CNAME Record

Determining a DCs objectGUID

To determine the objectGUID value of the joined domain controller "DC2", run on an existing DC:

# ldbsearch -H /usr/local/samba/private/sam.ldb '(invocationId=*)' --cross-ncs objectguid
# record 1
dn: CN=NTDS Settings,CN=DC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com
objectGUID: df4bdd8c-abc7-4779-b01e-4dd4553ca3e9

# record 2
dn: CN=NTDS Settings,CN=DC1,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samdom,DC=example,DC=com
objectGUID: 4a6bd92a-6612-4b15-aa8c-9ec371e8994f

# returned 2 records
# 2 entries
# 0 referrals

Locate the objectGUID of the DC in the output.

Verifying and Creating the objectGUID Record

To verify that the CNAME objectGUID record for domain controller (DC) "DC2" exists in the "_msdcs.samdom.example.com" DNS zone, run on a domain member:

# host -t CNAME df4bdd8c-abc7-4779-b01e-4dd4553ca3e9._msdcs.samdom.example.com.
df4bdd8c-abc7-4779-b01e-4dd4553ca3e9._msdcs.samdom.example.com is an alias for DC2.samdom.example.com.

If the record is missing, the following error is displayed:

# host -t CNAME df4bdd8c-abc7-4779-b01e-4dd4553ca3e9._msdcs.samdom.example.com.
Host df4bdd8c-abc7-4779-b01e-4dd4553ca3e9._msdcs.samdom.example.com. not found: 3(NXDOMAIN)

To manually add the objectGUID CNAME record to the DNS server running on "DC1", use the objectGUID determined in section Determining a DCs objectGUID and run:

# samba-tool dns add DC1 _msdcs.samdom.example.com df4bdd8c-abc7-4779-b01e-4dd4553ca3e9 CNAME DC2.samdom.example.com -Uadministrator
Password for [SAMDOM\administrator]: 
Record added successfully

The directory replication automatically distributes the new record to all DCs.