Good Point in Press Release Study: Are E-comm Sites Ready for DDOS Attacks During Christmas Sales Season?

"Your ISP and/or your CDN may not be providing the protection you need—or thought you had—in case of a DDoS attack." 

http://www.itbusinessedge.com/blogs/data-security/is-your-site-doing-enough-to-prevent-a-ddos-attack.html