Improving DNS CDN Performance With edns-client-subnet

Several months ago I wrote about how third party DNS services often slow you down since a DNS query is only one part of the equation and many websites use DNS to help their CDN figure out what servers are closest (and fastest). A few proposals to fix this have floated around, one is finally making headway.

Google, Bitgravity, CDNetworks, DNS.com and Edgecast have deployed support for edns-client-subnet. The idea is pretty simple. It passes part of your IP address (only part as to keep it semi-anonymous) in the request. A server that supports this extension can use it to geotarget and find a CDN node closest to you. Previously the best that could be done was using the location of the DNS server, which in many cases could be far away.

Still missing is support from some heavyweights like Akamai, who is the largest CDN, Limelight Networks and Level3. This is a pretty solid proposal with minimal negative implications. They are only passing part of the origin IP address, so it wouldn’t be a privacy invasion. In theory any website you browse could already harvest the IP you are using, this is just making part of it accessible to a partner who is already serving data on their behalf.

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