When managing large BIND DNS installations with thousands of zone files (like your 2000+ zone setup), the conventional service named restart approach becomes problematic. The complete shutdown and restart cycle:

• Terminates all running BIND processes immediately
• Requires full zone file reload during startup
• Causes 50-60 seconds of complete DNS unavailability

BIND includes the rndc (Remote Name Daemon Control) utility specifically for runtime management:

# Basic reload command
rndc reload

# Reload specific zone only
rndc reload example.com

# Verify current status
rndc status

To ensure smooth reload operations:

# Example named.conf zone configuration
zone "example.com" {
    type master;
    file "/var/named/zones/example.com.zone";
    allow-update { none; };
    notify yes;
    check-names ignore;
};

Key configuration parameters:

• notify yes - Enables automatic slave notification
• check-names ignore - Reduces reload validation time
• Consistent file permissions (typically named:named)

For mission-critical environments, consider these patterns:

# Pre-test zone files before reload
named-checkzone example.com /var/named/zones/example.com.zone

# Sequential zone reloads (for very large installations)
for zone in $(ls /var/named/zones/*.zone); do
    zone_name=$(basename $zone .zone)
    rndc reload $zone_name
    sleep 1
done

Specific tuning for BIND 9.3.6:

// Add to named.conf options
options {
    // Reduce memory usage during reloads
    cleaning-interval 120;
    max-cache-size 50%;
    
    // Disable features not needed
    empty-zones-enable no;
    auth-nxdomain no;
};

Track reload operations with these tools:

# Check reload timing in system logs
grep 'reloading configuration succeeded' /var/log/messages

# Monitor memory usage during reload
watch -n1 "ps -eo pid,user,cmd,%mem | grep named"

When managing a BIND DNS server with thousands of zone files (like in your case with 2000+ zones), using service named restart creates unnecessary downtime. The full restart process:

1. Terminates all running named processes
2. Performs zone file integrity checks
3. Re-loads all zones from disk
4. Rebuilds in-memory databases

This explains why your CentOS 5.5 server with BIND 9.3.6 takes 50-60 seconds to restart, during which DNS resolution fails.

For zone file changes, you should use these commands instead:

# Syntax checking before applying changes
named-checkconf /etc/named.conf
named-checkzone example.com /var/named/example.com.zone

# The proper reload command (preserves existing connections)
rndc reload
# Or alternatively:
/etc/init.d/named reload

For environments with thousands of zones, consider these optimizations:

Incremental Zone Reloads

Reload specific zones instead of all zones:

rndc reload example.com
rndc reload subdomain.example.com

Configuration Tuning

Add these options to named.conf:

options {
    // Faster zone loading
    check-names master ignore;
    check-mx ignore;
    
    // Reduce reload impact
    serial-query-rate 100;
    serial-queries 1000;
};

Check reload times with:

rndc status | grep "reload started"
tail -f /var/log/named.log | grep "reloading"

Typical output should show sub-second reloads for individual zones:

zone example.com/IN: loaded serial 2023081501 (0.3 seconds)

For your specific environment (CentOS 5.5 + BIND 9.3.6):

• Verify your rndc configuration exists in /etc/rndc.conf
• Older versions may require full path: /usr/sbin/rndc reload
• Monitor memory usage as BIND 9.3 has known memory leaks