domain access & domain resolution

Q: What are the requirements for domains to access CDN acceleration?

A:When accessing CDN acceleration, the business content of the source station in the acceleration area must be legal.

Q: What is the difference between page acceleration, download acceleration, and on-demand acceleration, and how should I choose?

A: Difference: Different acceleration contents, page acceleration is mainly for small files such as web page files and image files; download acceleration is mainly for large files such as installation packages and compressed packages; and on-demand acceleration is mainly for video files such as MP4 files.

Choose: Generally, if the file is larger than 5M, it is recommended to access the large file platform, and if it is a video file, choose on-demand acceleration.

Q: Whether to support pan-domain acceleration

A: It supports pan-domain acceleration: using wildcard to accelerate the domain, which is used to accelerate all the sub-domains; for example, if the accelerated domain configured by UCDN is "", the corresponding sub-domains,, can be resolve to the CNAME of UCDN's corresponding generic domain for acceleration.

domain configuration

Q: How long does it take to configure CDN?

A: CDN configuration generally takes less than 30 minutes, if the waiting time is more than 30 minutes after you setup, you can contact technical support to assist you in time.

Q: Are (opens in a new tab) and (opens in a new tab) recognized as two different files?

A: Whether they are different files or not depends on your configuration. If you configure ignore parameter caching, the two issues will be treated as the same file. If you don't configure ignore parameter cache, it will be judged as two different files.

By default, download acceleration and VOD acceleration ignore parameter caching, while page acceleration does not ignore parameter caching.

Q: What are the default caching rules for different acceleration types?

A:Page Acceleration: By default, dynamic files such as php, aspx, asp, jsp, do, dwr, etc. are not cached and are directly passed through, shtml, html, htm, js types are cached for 1 day by default, and other types of static files are cached for half a day by default. Page acceleration does not ignore parameter caching by default.

Download acceleration and on-demand acceleration: by default, all files are cached for 30 days, and parameter caching is ignored by default.

Q: What is the caching policy hierarchy when the Cache-Control field is present in the Response HTTP Header of the source?

  • If the Cache-Control field is max-age, the caching time of the resource is based on the caching time configured by the accelerated domain, and does not inherit the time specified by max-age.
  • If the Cache-Control field is no-cache or no-store, the CDN node does not cache this resource.
  • If there is no Cache-Control field in the Response HTTP Header, the caching time configured by the accelerated domain is the main focus.

Q: Does it support MD5 anti-theft chain and how to configure the accelerated domain for anti-theft chain?

A:Support MD5 anti-theft chain, users need to provide the specified secret key, synchronized technical support for configuration

k = md5(key + file URI + expiration time t)

1、k: parameter name in URL, md5(string value), the string generated by md5 is 32 bits.

2, t: expiration time, such as the current is 2012-04-23 16:20:00 set the effective length of 2 hours, that is, the expiration time of 2012-04-23 18:20:00 converted to 1970 based on the number of seconds 1335176400, that is, the value of parameter t. 3: key: the user to provide the secret password, md5 (string value), md5 generated string is 32-bit.

3: key: the user provides the secret key string.

Example: URL: (opens in a new tab)

Key: whaty321;

Expiration time: 2 hours. If 2019-07-01 12:00 expires, t=1561953600 after conversion;


URL after adding the anti-theft link: (opens in a new tab)

The URL using the anti-theft chain can be accessed normally, if k does not correspond to the access is invalidated, if the checksum finds that the time of t has exceeded the effective length, the checksum will also fail.

Prefetch push

Q: CDN refreshing prefetch limit

A: The daily refresh limit for single domain is 700 entries for files and 20 entries for directories; the prefetching limit is 500 entries.

Q: Will the traffic generated during CDN prefetching be billed?

A: After accessing CDN acceleration, the traffic generated during prefetching will not be charged.

Q: After refreshing the files, are the files on the CDN nodes already up-to-date?

A: No, after refreshing the files, the cached files on the CDN node will be cleared. When the user initiates a request again, since the file is not cached on the CDN node, it will pull the file back to the source and cache the file according to the caching rules configured for the accelerated domain.

Caching related questions

Q: How can I tell if user accessed content is hit on a CDN node?

A: You can check it through the developer tool of your browser or "curl - I + file URL ". If it is cached, then it is showing hit. When it is hit, it means that the CDN node has cached the content requested by the user. If miss, then the CDN node and for the cache to change the content, at this time will be back to the source to obtain data to respond to the user, at the same time will be configured according to the domain of the caching policy, the content will be cached on the CDN node.

Q: The content of the website has been updated, but why is it still the same as the old content after opening the page?

A: After using CDN acceleration, the files will be cached on the CDN nodes according to the caching policy configured for the domain. Since the caching time has not expired, it will appear that the file accessed by the user is still the old content. It is recommended to refresh the corresponding content when website content update occurs.

Q: Why is the CDN hit rate lower?

A: Generally, it depends on the hot spots of user data. The larger the access volume of the file, the higher the hit rate will be accordingly; under normal circumstances, the hit rate of download service is higher, above 95%, on-demand service is around 90%, the hit rate of web page file is lower, and some dynamic resources, the hit rate is related to the nature of its website, basically around 75%.

Lower hit rate is mainly ranked as follows:

  • Website visits are low, the file is not hot enough, the CDN node receives fewer requests, the effective caching of the file is less, resulting in the user's request can not be hit in the node, affecting the hit rate is low.
  • Accelerate the domain of the cache rules configuration is unreasonable, for some files set the cache length is shorter or not cache, resulting in frequent CDN nodes back to the source, the hit rate is reduced
  • The source station's cache HTTP Header is improperly set, the Header contains no-cache, cache-control=0, etc., which will be treated by the CDN as the highest priority to perform not caching.
  • The source station has more dynamic resources, mostly non-cacheable content, which will also lead to frequent pulling back to the source.

Q: How to get the end-user IP?

A:After formally switching to CDN service, when the request passes through the edge acceleration node, the x-forward-for header will be added by default, which carries the real IP information of the client, and the logs will also save the IP of the requested user.

Q: What should I do if the content obtained by CDN is inconsistent with the source site?

A:First determine whether the MD5 of the file is consistent or not,

If the files are not consistent, you can refresh the resources in the content management of the console. It usually takes about 5~10 minutes for the refresh to complete.

Q: When creating a CDN-accelerated domain, the domain acceleration type is selected wrongly, eg: business is website acceleration, and download acceleration is selected for creation, can it be modified?

A: You can't modify the acceleration type, you can delete the domain and re-create it. You can delete the domain and re-create it. Different acceleration types do not support mutual switching.

Data Collection

Q: Where do the bandwidth and traffic data collected by Real-Time Monitor come from?

A: The traffic and bandwidth data of the accelerated domains under the real-time monitoring display account comes from the downstream bandwidth/traffic of all the nodes, excluding the return bandwidth/traffic.

Q: How do the real-time monitoring hit bandwidth, traffic, request count and hit rate data come from the calculation?

A: Bandwidth statistics are based on 1-minute (the smallest display unit) peaks added up / the average of time granularity statistics, such as time granularity is 5 minutes, the bandwidth value is 5 1-minute bandwidth peaks added up / 5; traffic and request data is added up every minute; hit rate = percentage of byte hits in each time interval.

Q: How long is the real-time monitoring data latency?

A: The data latency is around 15-25 minutes.

Anomaly troubleshooting

Q: How to locate CDN anomalies initially?

A: 1. Open the hosts file, which is usually stored in: C:\Windows\System32\drivers\etc directory

2.Add the source IP and the corresponding faulty domain. (e.g. (opens in a new tab) with a space between them and the IP in front)

  1. Save the hosts file modification, and restart the browser, visit the domain to see if there is still a problem accessing, if there is still a problem, it is the source station failure, if the access is normal, please contact SurferCloud technical support in time.

Q: Why stop UCDN domain acceleration and still incur bandwidth and fees?

A: The user's local DNS still has a DNS resolution cache, and during the period when the cache has not expired, it will be requested to the corresponding node, generating a small amount of bandwidth traffic, and the DNS resolution cache time is controlled by the operators in each region.

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