Suppose we now have the domain name <your-domain>. We can use the API provided by a DNS provider, using Cloudflare as an example, to periodically update the IPv6 address.

1. Add an AAAA DNS Record (Pointing to Your IPv6 Address)

Log in to https://dash.cloudflare.com, add your domain to Cloudflare, and replace the DNS nameservers at your domain registrar with the nameservers provided by Cloudflare.

Then add the following record in the DNS management panel for your domain:

text
Type      Name     IPv6 Address       Proxy Status     TTL
AAAA      www      <any value>        DNS only         2 minutes

On the Cloudflare dashboard, open the overview page for the domain and obtain your API token. Also note the Zone ID of your domain.

2. Install the DDNS Script

Install the required software on Debian-based systems:

bash
sudo apt install curl jq

Create the following script at /usr/local/bin/ddns-ipv6.sh. Be sure to modify the configuration section:

bash
#!/bin/bash

LOGFILE="/var/log/ddns-ipv6.log"
LAST_IP_FILE="/var/tmp/last_ipv6.txt"

touch $LOGFILE
chmod 644 $LOGFILE

echo "=== $(date) Starting DDNS update ===" >> $LOGFILE

# Configuration
CF_API_TOKEN="<your Cloudflare API Token>"
CF_ZONE_ID="<your Zone ID>"
RECORD_NAME="<your domain>"
NET_INTERFACE="enp0s31f6"  # Replace with your actual network interface
TTL=120

# Logging function
log() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" | tee -a $LOGFILE
}

# Try multiple methods to obtain a reliable public IPv6 address
get_ipv6() {
    local ip_system=$(ip -6 addr show dev $NET_INTERFACE scope global \
        | grep -E 'global (dynamic|mngtmpaddr|temporary|permanent)' \
        | awk '/inet6/{print $2}' | cut -d'/' -f1 | head -1)

    local ip_api=$(curl -6 --connect-timeout 5 -s https://api64.ipify.org || \
                   curl -6 --connect-timeout 5 -s https://ipv6.icanhazip.com)

    [ -n "$ip_system" ] && echo $ip_system || echo $ip_api
}

# Get the current IPv6 address
IP=$(get_ipv6)

if [ -z "$IP" ]; then
    log "Error: Unable to obtain a valid IPv6 address"
    exit 1
fi

log "Detected IPv6 address: $IP"

# Read the previous IP address
if [ -f "$LAST_IP_FILE" ]; then
    LAST_IP=$(cat "$LAST_IP_FILE")
    if [ "$IP" = "$LAST_IP" ]; then
        log "IPv6 address has not changed; no update required ($IP)"
        echo "=== $(date) Finished DDNS update ===" >> $LOGFILE
        exit 0
    else
        log "IPv6 address change detected: $LAST_IP → $IP"
    fi
else
    log "First run: no previous IP address found"
fi

# Get the DNS record ID
RESPONSE=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones/$CF_ZONE_ID/dns_records?type=AAAA&name=$RECORD_NAME" \
    -H "Authorization: Bearer $CF_API_TOKEN" \
    -H "Content-Type: application/json")

SUCCESS=$(echo "$RESPONSE" | jq -r '.success')
if [ "$SUCCESS" != "true" ]; then
    ERRORS=$(echo "$RESPONSE" | jq -r '.errors[]?.message')
    log "Error: Failed to retrieve record ID - $ERRORS"
    exit 1
fi

RECORD_ID=$(echo "$RESPONSE" | jq -r '.result[0].id')

if [ -z "$RECORD_ID" ] || [ "$RECORD_ID" = "null" ]; then
    log "Error: Record $RECORD_NAME was not found. Please create this AAAA record in Cloudflare first."
    exit 1
fi

log "Record ID found: $RECORD_ID"

# Update the DNS record
UPDATE_RESPONSE=$(curl -s -X PUT "https://api.cloudflare.com/client/v4/zones/$CF_ZONE_ID/dns_records/$RECORD_ID" \
    -H "Authorization: Bearer $CF_API_TOKEN" \
    -H "Content-Type: application/json" \
    --data "{\"type\":\"AAAA\",\"name\":\"$RECORD_NAME\",\"content\":\"$IP\",\"ttl\":$TTL,\"proxied\":false}")

UPDATE_SUCCESS=$(echo "$UPDATE_RESPONSE" | jq -r '.success')
if [ "$UPDATE_SUCCESS" = "true" ]; then
    NEW_CONTENT=$(echo "$UPDATE_RESPONSE" | jq -r '.result.content')
    log "Record updated successfully! $RECORD_NAME → $NEW_CONTENT"
    echo "$IP" > "$LAST_IP_FILE"   # Save the new IP address
else
    ERRORS=$(echo "$UPDATE_RESPONSE" | jq -r '.errors[]?.message')
    log "Error: Failed to update the DNS record - $ERRORS"
    exit 1
fi

echo "=== $(date) Finished DDNS update ===" >> $LOGFILE

Then make the script executable:

bash
chmod +x /usr/local/bin/ddns-ipv6.sh

3. Use a Crontab Job to Update It Automatically

Open your crontab:

bash
crontab -e

Add the following line:

bash
*/5 * * * * /usr/local/bin/ddns-ipv6.sh >/var/log/ddns-ipv6.log 2>&1

This checks for IPv6 address changes every five minutes and automatically updates the DNS record when necessary.