There is an internet plan in my ISP that allows only Facebook, and because Facebook uses Akamai it is included also. So any server that belongs to Akamai can be accessed. How does the firewall know all the servers of Akamai because requesting the IP address of the server works fine, so it's not based on domain name.
I did a little searching Firewall defined Akamai IP Range
and I found out that it is not possible to know all the servers, so any theories and how can I confirm it?
In most cases people gather lists of big companies IP address ranges from their BGP AS numbers which are associated with ranges of IP addresses. A quick search at a public BGP AS looking glass reveals many lists for Akamai IP addresses these can then be aggregated and blocked by your firewall.
This technique usually won't work for smaller companies as they are less likely to use BGP. It also has many limitations in that a company may host servers on another companies network (think cloud compute services) and those servers will not show up under the companies BGP AS IP ranges. None the less, for blocking access to large well-known services this is an easy way to find a companies IP address ranges.
http://bgp.he.net/search?search%5Bsearch%5D=akamai&commit=Search
