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Our web system, use the third-party cdn service. Assume that the user set the local dns with the googledns or opendns to visit our web sites, so cdn service will select the closest cdn proxy node. all right, but in fact the user's actual access position might outside there, cdn service may chose the one furthest away from the user node, so static resource access slower..

At present, my idea is if user local set dns server with googledns, and then first one we get the actual ip address of the user, tracerote to test a best routing lines, set up a cookie in user browser, and then set 302 header for response to jump to the which best cdn node.

Whether the user's browser side traceroute tool can provide the best route decision-making ?

Because we find that, once the user to set local dns server with the foreign network segment, for example : set dns with 8.8.8.8, so cdn routing will choose the foreign service node.

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migrated from stackoverflow.com Feb 9 '12 at 14:12

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3 Answers 3

The big CDN networks do various routing tricks to try to ensure the user communicates with their closest proxy. This is normally not visible to you, so as long as you let the CDN manage the advertised DNS addresses, and let the CDN do its job, it should be doing the best it can.

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However, if the local dns is set to opendns or googledns, cdn service providers according to user set of the dns address routing static resource to the foreign cdn nodes, In fact, it is the farthest away from the user.. –  Tony Lee Feb 7 '12 at 6:05

I think the real question you want to be asking is: why is latency such a concern in my application?

Unless you're doing something really specialized, I doubt you really need to worry about this.

Also, remember, your operations are not free either! You're making the user wait for your "diagnostics" to optimize for the best network path.

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Is there any way to improve the routing quality of CDN ? –  Tony Lee Feb 9 '12 at 6:02

With some notable exceptions then the fast CDNs use either Anycast which is "pure networking" (DNS doesn't come into play) or EDNS-SUBNET (supported by OpenDNS and Google's public DNS service) or a combination of the two to work around this issue.

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