This document explains the procedure for constructing a DNS server and configuring clients to meet the requirements of Oracle Real Application Clusters (Oracle RAC) / Grid Infrastructure (GI) in the following mixed OS environment.
- DNS Server: Oracle Linux 7 (OL7)
- RAC Nodes: Oracle Linux 8 (OL8)
1. Design Information
| Item | Setting Value | Remarks |
|---|---|---|
| Role | DNS Server IP | 192.168.56.18 |
| Domain Name | example.local | Domain for RAC environment |
| RAC Node 1 (Public) | 192.168.56.61 | OL8 (rac-26ai1) |
| RAC Node 2 (Public) | 192.168.56.62 | OL8 (rac-26ai2) |
| Virtual IP (VIP) | 192.168.56.63, 64 | Virtual IP for each node |
| SCAN IP | 192.168.56.65, 66, 67 | Common access IPs (Set of 3) |
2. Construction of DNS Server Side (OL7: 192.168.56.18)
2.1 Installing BIND
yum install bind bind-utils -y
2.2 Main Configuration File (/etc/named.conf)
The directory "/var/named"; is a mandatory setting.
vi /etc/named.conf
[Configuration Content]
options {
listen-on port 53 { 127.0.0.1; 192.168.56.18; };
directory "/var/named";
allow-query { localhost; 192.168.56.0/24; };
recursion yes;
dnssec-enable no;
dnssec-validation no;
bindkeys-file "/etc/named.root.key";
managed-keys-directory "/var/named/dynamic";
pid-file "/run/named/named.pid";
session-keyfile "/run/named/session.key";
};
zone "example.local" IN {
type master;
file "example.local.zone";
};
zone "56.168.192.in-addr.arpa" IN {
type master;
file "192.168.56.rev";
};
2.3 Creating the Forward Zone File
For SCAN, ensure that three IPs are registered with the same hostname.
vi /var/named/example.local.zone
[Configuration Content]
$TTL 86400
@ IN SOA dns-server.example.local. root.example.local. (
2025062201 ; Serial
3600 ; Refresh
1800 ; Retry
604800 ; Expire
86400 ) ; Minimum TTL
IN NS dns-server.example.local.
dns-server IN A 192.168.56.18
; --- Public IP ---
rac-26ai1 IN A 192.168.56.61
rac-26ai2 IN A 192.168.56.62
; --- Virtual IP (VIP) ---
rac-26ai1-vip IN A 192.168.56.63
rac-26ai2-vip IN A 192.168.56.64
; --- SCAN (Register 3 IPs) ---
rac-26ai-scan IN A 192.168.56.65
rac-26ai-scan IN A 192.168.56.66
rac-26ai-scan IN A 192.168.56.67
; --- Private IP (Optional) ---
rac-26ai1-pr IN A 192.168.57.61
rac-26ai2-pr IN A 192.168.57.62
2.4 Creating the Reverse Zone File
Describe PTR records without any omissions.
vi /var/named/192.168.56.rev
[Configuration Content]
$TTL 86400
@ IN SOA dns-server.example.local. root.example.local. (
2025062201 ; Serial
3600 ; Refresh
1800 ; Retry
604800 ; Expire
86400 ) ; Minimum TTL
IN NS dns-server.example.local.
18 IN PTR dns-server.example.local.
61 IN PTR rac-26ai1.example.local.
62 IN PTR rac-26ai2.example.local.
63 IN PTR rac-26ai1-vip.example.local.
64 IN PTR rac-26ai2-vip.example.local.
65 IN PTR rac-26ai-scan.example.local.
66 IN PTR rac-26ai-scan.example.local.
67 IN PTR rac-26ai-scan.example.local.
2.5 Permission Settings and SELinux Application
Always re-execute these steps if you delete and recreate the files.
chown root:named /etc/named.conf /var/named/example.local.zone /var/named/192.168.56.rev
chmod 640 /etc/named.conf /var/named/example.local.zone /var/named/192.168.56.rev
restorecon -v /etc/named.conf
restorecon -Rv /var/named
named-checkconf -z /etc/named.conf
systemctl enable --now named
firewall-cmd --add-service=dns --permanent && firewall-cmd --reload
2.6 Checking DNS Server Operation and Status
# 1. Check service status
systemctl status named
# 2. Check detailed BIND operational status
rndc status
# 3. Check listening ports (53/UDP/TCP)
ss -antup | grep :53
# 4. Monitor real-time logs
journalctl -u named -f
3. Configuration of RAC Node Side (OL8 Client)
The following is the recommended procedure for persisting edits to /etc/resolv.conf on OL8.
3.1 Persistence via NetworkManager (nmcli)
Perform this on each node.
# 1. Check active connection names
nmcli connection show
# 2. Register DNS server and search domain
# Replace "Connection Name" with the name confirmed in step 1
nmcli connection modify "Connection Name" ipv4.dns "192.168.56.18"
nmcli connection modify "Connection Name" ipv4.dns-search "example.local"
# 3. Apply changes (This automatically updates /etc/resolv.conf)
nmcli connection up "Connection Name"
3.2 Final Confirmation of Settings
cat /etc/resolv.conf
# Success if "search example.local" and "nameserver 192.168.56.18" exist
4. Pre-installation Final Confirmation Checklist
- SCAN Round Robin: Does the order of IPs change every time you execute
nslookup rac-26ai-scan? - Short Name Connectivity: Do you get a response from
ping rac-26ai2? (Verification of search settings). - Reverse Lookup Match: Does
nslookup 192.168.56.65, etc., return the correct hostname?
5. FAQ (Frequently Asked Questions)
Q1: Why are three SCAN IPs necessary? A1: This is an Oracle best practice and a verification item for the Grid Infrastructure installer. Configuring three IPs achieves load balancing and high availability through DNS round-robin during client connections.
Q2: Why shouldn’t I edit /etc/resolv.conf directly? A2: In OL8, NetworkManager manages this file. Therefore, manual settings will be automatically overwritten (erased) during a reboot or network disconnection. Using nmcli saves the settings into the profile, ensuring persistence.
Q3: nslookup works, but ping does not. A3: Check if search example.local is described in /etc/resolv.conf. If it is missing, ping rac-26ai1 without the domain name will fail. Also, check if old entries remain in /etc/hosts, as the hosts: files dns order in /etc/nsswitch.conf may cause failures.
Q4: What happens if I forget to update the DNS server’s serial value? A4: Even if you modify the records, the changes may not be reflected unless you increment the Serial value and restart the service (or run rndc reload).
6. Summary
- SCAN Configuration: Defining three A records for a single hostname using “DNS Round Robin” is the core of the RAC configuration.
- Permissions and SELinux: Files under
/var/namedmust have thenamedgroup as the owner, and the security context must be set correctly withrestorecon; otherwise,namedcannot read the files. - OL8 Network Management: Mastering
nmclicommands for persistence on OL8 clients is the only way to prevent future issues (inability to resolve names after a reboot).
コメント