This topic provides answers to some frequently asked questions about Web Application Firewall (WAF).

Can I use WAF to protect servers that are not deployed on Alibaba Cloud?

Yes, you can use WAF to protect servers that are not deployed on Alibaba Cloud. WAF protects all servers that are accessible over the Internet. These servers can be deployed on Alibaba Cloud or third-party clouds, or in data centers.
Notice If you want to add domain names to a WAF instance in mainland China, you must complete Internet Content Provider (ICP) filing for the domain names. ICP filing is required by the Ministry of Industry and Information Technology (MIIT). If the domain names do not have ICP filing, the domain names cannot be added to the WAF instance.

Does WAF support Cloud Web Hosting instances?

Yes, all editions of WAF support exclusive Cloud Web Hosting instances. After you activate WAF, you can configure exclusive instances in the WAF console.

Shared Cloud Web Hosting instances use shared IP addresses, which means that multiple users share the same origin server. We recommend that you do not configure WAF for shared instances.

Can WAF protect HTTPS services?

Yes, all editions of WAF can protect HTTPS services. You can add wildcard domain names to WAF.

To protect HTTPS services, you must upload SSL certificates and private key files as prompted. After HTTPS-enabled websites are added to WAF, WAF decrypts access requests, checks request packets, encrypts the requests, and then forwards the requests to origin servers.

Does WAF support custom ports?

The Business and Enterprise editions of WAF support custom non-standard ports. The WAF Business edition supports up to 10 non-standard ports, and the WAF Enterprise edition supports up to 50 non-standard ports.
Notice WAF supports non-standard ports only within a specific port range. The non-standard ports must be within the allowed port range. For more information, see View the allowed port range.

Does the QPS limit that is configured for a WAF instance in the WAF console apply to the entire WAF instance or a single domain name added to the WAF instance?

The queries per second (QPS) limit applies to the entire WAF instance.

For example, if you add three domain names to a WAF instance in the WAF console, the total QPS of these domain names cannot exceed the configured QPS limit. If the total QPS exceeds the limit, WAF triggers throttling and may discard packets at random.

Does WAF support two-way HTTPS authentication?

No, WAF does not support two-way HTTPS authentication.

Does WAF support the WebSocket, HTTP/2, and SPDY protocols?

All editions of WAF support WebSocket. WAF Business and higher editions support HTTP/2. WAF does not support SPDY.

Is the origin server affected if you add HTTP/2 services to WAF?

Yes, the origin server is affected. If you add HTTP/2 services to WAF, WAF can handle HTTP/2 requests from clients, but WAF can forward requests to the origin server only over HTTP 1.0 or 1.1. Therefore, if HTTP/2 services are added to WAF, HTTP/2 multiplexing cannot work as expected and the clean bandwidth of the origin server increases.

Which TLS protocols does WAF support?

WAF instances that reside in mainland China support TLS 1.0, TLS 1.1, and TLS 1.2. WAF instances that reside outside mainland China support TLS 1.1 and TLS 1.2.

If you have personalized requirements, you can customize TLS configurations. For example, you can disable TLS 1.0 and enable TLS 1.3 for your WAF instance. For more information, see Configure custom TLS settings.

Can WAF protect websites that use NTLM authentication?

No, WAF cannot protect websites that use New Technology LAN Manager (NTLM) authentication. If your website uses NTLM authentication, the access requests forwarded by WAF may fail to pass the NTLM authentication of an origin server. As a result, authentication prompts may be repeatedly displayed on the client. We recommend that you use a different authentication method for your website.

Can I use the internal IP address of an ECS instance as an origin IP address in the WAF console?

No, you cannot use the internal IP address of an Elastic Compute Service (ECS) instance as an origin IP address. The reason is that WAF forwards requests to an origin server over the Internet.

Can WAF protect multiple origin IP addresses for one domain name?

Yes, you can enter a maximum of 20 origin IP addresses when you add a domain name in the WAF console.

How does WAF balance request loads among origin servers?

If you configure multiple origin servers, WAF automatically uses the IP hash method to balance request loads among these origin servers. You can also use other load balancing algorithms based on your business requirements. For more information, see Add a website.

Does WAF support the health check feature?

Yes, WAF supports the health check feature, which is enabled by default. WAF checks the availability of origin IP addresses. If an origin server is unavailable, WAF forwards the requests to another origin server.
Note If an origin server does not respond, WAF sets a cooldown period for the origin server. During the period, WAF does not forward requests to the origin server but forwards the requests to another origin server. After the period elapses, new requests may be forwarded to the faulty origin server again. For more information about how the health check feature works, see Health check overview.

Does WAF support session persistence?

Yes, WAF supports session persistence, which is disabled by default. If you want to enable session persistence, submit a ticket to contact technical support.

Does latency occur when I change an origin IP address in the WAF console?

Yes, latency occurs when you change an origin IP address. The new IP address requires about 1 minute to take effect.

What are the back-to-origin CIDR blocks of WAF?

You can perform the following operations to query back-to-origin CIDR blocks: Log on to the WAF console and choose System Management > Product Information. For more information, see Allow access from back-to-origin CIDR blocks of WAF.

Does WAF automatically add its back-to-origin CIDR blocks to security groups?

No, WAF does not automatically add its back-to-origin CIDR blocks to security groups. If you deploy other firewalls or host protection software for origin servers, we recommend that you add the back-to-origin CIDR blocks of WAF to the required whitelists.

We recommend that you configure specific protection policies for the origin servers. For more information, see Configure protection for an origin server.

Do I need to allow access requests from all client IP addresses?

You can allow access requests from all client IP addresses or only from the back-to-origin CIDR blocks of WAF. To protect web services of origin servers, we recommend that you allow access requests only from the back-to-origin CIDR blocks of WAF.

Can a WAF instance that uses an exclusive IP address defend against DDoS attacks?

Yes, a WAF instance that uses an exclusive IP address can defend against DDoS attacks.

WAF provides exclusive IP addresses for users. Blackhole filtering that defends against DDoS attacks can apply to these IP addresses, similar to the IP addresses of ECS and Server Load Balancer (SLB) instances. The default DDoS mitigation capability provided by the WAF instance that uses an exclusive IP address is the same as the DDoS mitigation capability of an ECS instance in the region where WAF is deployed.

Can WAF be deployed with CDN or with Anti-DDoS Pro or Anti-DDoS Premium?

Yes, WAF is fully compatible with Alibaba Cloud Content Delivery Network (CDN), Anti-DDoS Pro, and Anti-DDoS Premium. If you want to deploy WAF with CDN and Anti-DDoS Pro or Anti-DDoS Premium, we recommend that you deploy the components in the following sequence: client, Anti-DDoS Pro or Anti-DDoS Premium, CDN, WAF, SLB, and origin server.

If you want to deploy WAF with CDN or with Anti-DDoS Pro or Anti-DDoS Premium, set the address of the origin server to the CNAME assigned by WAF when you add a domain name to CDN, Anti-DDoS Pro, or Anti-DDoS Premium. In this case, requests are forwarded by CDN, Anti-DDoS Pro, or Anti-DDoS Premium to WAF and then to the origin server. This way, the origin server is protected. For more information, see Use WAF with Anti-DDoS Pro or Anti-DDoS Premium and Use WAF with CDN.

Can I deploy WAF with CDN and Anti-DDoS Pro or Anti-DDoS Premium by using different Alibaba Cloud accounts?

Yes, you can deploy WAF with CDN and Anti-DDoS Pro or Anti-DDoS Premium by using different accounts. This deployment mode allows you to defend against DDoS attacks and web application attacks.

How does WAF ensure the security of an uploaded certificate and its private key? Does WAF decrypt HTTPS traffic and record the content of HTTPS requests?

If you use WAF to protect HTTPS services, you must upload the required SSL certificate and its private key. This way, WAF can decrypt HTTPS traffic to detect attacks and analyze the characteristics of attacks. Alibaba Cloud uses a dedicated key server to store and manage private keys. The key server is based on Alibaba Cloud Key Management Service (KMS) and can ensure the data security, integrity, and availability of both certificates and private keys. This helps meet the requirements for regulation, classified protection, and compliance. For more information about KMS, see What is Key Management Service?.

WAF uses an uploaded certificate and its private key to decrypt HTTPS traffic only in the scenarios when they detect attacks in real time. WAF records only specific content of request payloads. The content is determined based on attack characteristics. Then, WAF can provide attack reports and data statistics based on the content. WAF can record the full content of requests or responses only when WAF is authorized.

WAF has been accredited against authoritative standards, including ISO 9001, ISO 20000, ISO 22301, ISO 27001, ISO 27017, ISO 27018, ISO 27701, ISO 29151, BS 10012, Cloud Security Alliance (CSA) STAR, MLPS level 3, Service Organization Control (SOC) 1, SOC 2, SOC 3, Cloud Computing Compliance Criteria Catalogue (C5), Green Finance Certification Scheme developed by Hong Kong Quality Assurance Agency (HKQAA), Outsourced Service Providers Audit Report (OSPAR), and Payment Card Industry Data Security Standard (PCI DSS). The standards also include those that prove the effectiveness of WAF across financial sectors in Hong Kong (China). WAF also provides the same security and compliance qualifications as Alibaba Cloud. For more information, visit Alibaba Cloud Trust Center.

Note If you use WAF to protect HTTPS services, you can use a dual-certificate method. This method allows you to independently use a set of certificate and private key on both your WAF instance and the origin server. The two sets of certificates and private keys must be valid. This way, the key server can separately manage the certificates and keys.

How can I use WAF to defend against HTTP flood attacks?

WAF provides various protection modes to defend against HTTP flood attacks. You can select a mode based on your business requirements. For more information, see Configure HTTP flood protection.

To achieve better protection and reduce the occurrence of false positives, you can use the WAF Business edition or WAF Enterprise edition in which security experts tailor protection algorithms specific to your business. For more information, see Create a custom protection policy.

How long does it take for configuration modifications in the WAF console to take effect?

In most cases, configuration modifications take effect within 1 minute.

When I configure custom protection policies (ACL policies) in the WAF console, can I enter CIDR blocks in the IP field?

Yes, you can enter CIDR blocks in the IP field when you configure custom protection policies in the WAF console.

Why does a custom protection policy in which the URL match field contains two forward slashes (//) not take effect?

When the rules engine of WAF processes the URL match field, it compresses consecutive forward slashes (/). Therefore, the rules engine cannot match the custom protection policy because the URL match field contains two forward slashes (//).

If you want to define an ACL policy in which the URL match field contains two forward slashes (//), enter a single forward slash (/) instead. For example, if you want to set the URL match field to //api/sms/request, enter /api/sms/request instead. This way, WAF can implement access control based on the policy.

Can I view the source IP addresses of HTTP flood attacks in the WAF console?

Yes, you can view the source IP addresses of HTTP flood attacks after you enable Log Service of WAF. For more information, see Enable Log Service for WAF and Query logs.

How do I query the bandwidth usage of WAF?

You can query the bandwidth usage of WAF on the Overview page in the WAF console.