Menu
Recently, I saw I introduction on CDN at
http://www.aflexi.net/technology/how-aflexi-cdn-works
I was wondering, why user's web browser will know it need to contact Aflexi DNS Server in Los Angeles, but not DNS Server provided by ISP (Like AOL)?
Thanks!
457
CDNs typically perform dynamic request routing using the Internet's Domain Name System (DNS) [11]. The DNS is a distributed directory whose primary role is to map fully qualified domain names (FQDNs) to IP addresses. To determine an FQDN's address, a DNS client sends a request to its local DNS server.
If the DNS server is unavailable, the browser has no way of acquiring the website's IP address, so it returns an error. Now everyone knows the server is down because it only takes seconds for the news to spread.
A CDN is a network of servers that distributes content from an “origin” server throughout the world by caching content close to where each end user is accessing the internet via a web-enabled device. The content they request is first stored on the origin server and is then replicated and stored elsewhere as needed.
The client is then redirected to the CDN provider's DNS authoritative server which resolves the CDN domain name. In DNS-based server redirecting, the server selection result is delivered to the end user by resolving the domain name to the IP address of the selected surrogate server.
Your Internet Service Provider will likely push the DNS server information through the DHCP protocol (of course, you can override this information locally on your machine). This is how your machine will get configured with DNS servers to launch queries against.
The way a CDN works is as follows: companies relying on CDN based delivery of their contents will manage their domains through a CDN provider. When a request comes for say domain D, a machine will contact its configured DNS server and will be directed to the "authoritative entity" for the domain D in question. From this point, the CDN DNS server can reply with an answer that provides a binding to an IP address "closest" to where the request originated.
The property "closest" is determined, amongst other things, based on the requesting machine's IP address. It is nonetheless non-trivial to assign a "metric" based on this information: there is no direct correlation between "IP address" and "physical location", vital information for effecting as best as possible contents to the requesting machines.
179
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
