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Back up data for multi-link disaster recovery for ISPs

Last Updated: Sep 15, 2020

Scenarios

To accelerate access and provide good-quality services to broadband users of different Internet service providers (ISPs), the online application services of enterprises generally use the IP addresses of multiple ISPs and use the Domain Name System (DNS) for intelligent access. Assume that the same domain name is used.

  • If a China Unicom user requests the domain name, 1.1.1.1 is returned.
  • If a China Mobile user requests the domain name, 2.2.2.2 is returned.
  • If a user of any other ISP requests the domain name, 3.3.3.3 is returned.

When the IP address of an ISP is unavailable, the access traffic is automatically switched to the IP address of another ISP.

How it works

Global Traffic Manager (GTM) allows you to access different networks to resolve IP addresses. GTM also allows you to enable health check for each address pool and determine whether an IP address is unavailable based on the health check result. If a failure occurs, GTM switches user request traffic to an IP address of the same ISP in the alternative address pool, as shown in the following figure.

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Resources

  • A domain name, for example, www.dns-example.com. We recommend that you use the Enterprise Standard Edition of Alibaba Cloud DNS.
  • A GTM instance.
  • Three IP addresses: 1.1.1.1 (China Unicom), 2.2.2.2 (China Mobile), and 3.3.3.3 (China Telecom).

Configuration method

GTM configuration

1. Global settings

On the Global Settings tab, you can set the Primary Domain, CNAME Access Domain Name, Balance Policy, Global TTL, and Alert Group parameters. For more information, see Quick Start - Global settings.

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Note: When you use the IP address of an ISP, set CNAME Access Domain Name to Custom Access Domain Name. The custom access domain name can be any domain name filed on the website in the domain name resolution list under your current account.

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2. Address pool configurations

Create dedicated address pools for the IP addresses of different ISPs. This facilitates creation of access policies for visitors from different networks or regions. By using these access policies, visitors can connect to the nearest access points and implement automatic traffic switchover. For more information, see Create an address pool. Configure three address pools respectively for the following three IP addresses: 1.1.1.1 (China Unicom), 2.2.2.2 (China Mobile), and 3.3.3.3 (China Telecom), as shown in the following figure.

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3. Health check configuration

When you use GMT, you must enable health check for each address pool. In this way, when the IP address of an ISP fails, you can switch traffic to the IP address of a normal ISP. For more information, see Enable health check.

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4. Access policy configurations

Access policies include intelligent DNS resolution, default address pools and alternative address pools, and switchover policies of active address pools. You can set different resolution response address pools for visitors from different networks or regions, and they can connect to the nearest access points and implement automatic traffic switchover.

  • Add an access policy for which DNS Request Sources is set to Global. If it is not set to Global, the application may not be accessible in some regions. For example, Default Address Pool is set to China Telecom and Alternative Address Pool is set to China Unicom. If the China Telecom address pool is unavailable, the request traffic of the China Telecom address pool is automatically switched to the China Unicom address pool to ensure the stable operation of the application. The reference configuration is shown in the following figure.

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  • Create an access policy for China Unicom users, for which DNS Request Sources is set to ISP-China Unicom, Default Address Pool is set to China Unicom, and Alternative Address Pool is set to China Mobile. If the China Unicom address pool is unavailable, the request traffic of the China Unicom address pool is automatically switched to the China Mobile address pool to ensure the stable operation of the application. The reference configuration is shown in the following figure.

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  • Create an access policy for China Mobile users, for which DNS Request Sources is set to ISP-China Mobile, Default Address Pool is set to China Mobile, and Alternative Address Pool is set to China Telecom. If the China Mobile address pool is unavailable, the request traffic of the China Mobile address pool is automatically switched to the China Telecom address pool to ensure the stable operation of the application. The reference configuration is shown in the following figure.

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Verification

You can check whether the configuration is as expected after you complete GTM configuration.

  • Verify the access policy: You can access DNSChecker, click the Dns tab, and then check whether the IP addresses in the address pool of the access policy can be resolved.

  • Verify automatic switchover: You can disconnect the network of China Mobile, wait about 5 minutes, and then check whether the switchover policy takes effect. When the China Mobile address pool fails, the value of Default Address Pool automatically changes from China Mobile to China Telecom, as shown in the following figure. You can also perform the verification by following the instructions in Disaster recovery plans.

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Configuration of online access

If the configurations for GTM meet your expectations, you must map the primary domain name to the canonical domain name to achieve disaster recovery and smart access for your applications, as shown in the following figure. For more information, see CNAME access.

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Precautions

1 . If an IP address is an ISP IP address (that is, the address pool contains an IP address that is not an Alibaba Cloud IP address), you must set CNAME Access Domain Name to Custom Access Domain Name to avoid registration failure.

2 . If CNAME Access Domain Name is set to Custom Access Domain Name, use a domain name of the Enterprise Standard Edition of Alibaba Cloud DNS to achieve the optimal effect.

3 . GTM is a DNS-level service that switches domain names for disaster recovery. Therefore, its running status is affected by the DNS cache of ISPs in various provinces, which requires a specific period for cache update. 90% of online traffic can be switched within 5 to 10 minutes.