1 Feature Intro

1.1 Brief Introduction

When the customer uses the CDNetworks CDN service, the CDN PoPs will act as an origin to respond to user requests, and also as a user to interact with the origin server. CDNetworks supports multiple back-to-origin (Hereafter written as BtO) strategies including:

• Back-to-Origin by Origin Domain
• Back-to-Origin by Origin IP
• Alternate Back-to-Origin
• Back-to-Origin by User IP
• Back-to-Origin by ISP adoption
• User IP Forwarding

The BtO configuration is the primary and necessary configuration when using all the CDNetworks acceleration products. Customers will adopt different BtO policies according to their business characteristics.

1.2 Applicable Product Lines

• Content Acceleration
• Dynamic Web Acceleration
• Media Acceleration
• Media Acceleration Live Broadcast

2 Feature Detail

2.1 Back-to-Origin by Origin Domain

Customers provides the origin domain name. CDNetworks performs DNS resolution and the CDN server will go back to the origin with the resolved IP.

Application Scenario

This BtO strategy is applicable to customers whose origin IP addresses are unstable and change frequently.

2.2 Back-to-Origin by Origin IP

Customers provide their origin IP, and CDNetworks binds the acceleration domain name to the fixed origin IP.

Application Scenario

This strategy is recommended when customer origin’s IP address is stable and do not change frequently.

2.3 Alternate Back-to-Origin

Alternate BtO supports using different domain names and ports for CDN and BtO requests. For example: use domain A and port A for CDN requests, but use domain B and port B for BtO requests.

Application Scenario

Some customers do not use their own domains or regular ports for BtO requests. For example, the customer is using CDNetworks’ or AWS’ cloud origin, and the origin domain is provided by CDNetworks or AWS, so their domain/port for CDN requests will be different from the BtO domain/port. We recommend Alternate BtO solution for these customers.

2.4 Back-to-Origin by User IP

CDNetworks maintains the mapping between the user IP and the origin server IP to ensure that requests with the same user IP are resolved to the same origin server.

Application Scenario

If a user had sent a BtO request before, some customer would hope that the next BtO request sent by the same user will be resolved to the same origin server (to keep the login status for the user). CDNetworks recommends the BtO by user IP strategy for these customers.

2.5 Back-to-Origin by ISP Adoption

When a customer’s origins are dispersed in different ISP networks, BtO by ISP guarantees that the BtO request go back to the origin of the corresponding ISP. By this way, the cross-network BtO request is avoided, and the cross-network time is saved.

Application Scenario

It is recommended when a customer has multiple origins deployed in different ISP networks.

2.6 User IP Forwarding

With User IP Forwarding, CDNetworks will add the IP address of the end user in the HTTP header “Cdn-Src-IP” or “X-Forward-For” when sending the BtO request to the origin.
CDNetworks also supports other custom HTTP headers when requested by customers. In this way, customers can collect the user IP information.

Application Scenario

It is used when customer needs to collect user IP information.

3 Notices

If the BtO domain or IP changes, customer needs to timely inform CDNetworks to ensure the mapping between the acceleration domain/IP and origin has been updated. Otherwise, it will affect the BtO requests and ultimately affect the service of customers.