Some networks have a firewall configured to restrict access to outside servers based on an ACL (Access Control List) containing the IP addresses of all allowed servers. Because Akamai's server IPs change frequently, users behind these networks may see broken pages or images if all Akamai server IP addresses are not included in the ACL.
A network administrator with this configuration would typically add additional IP addresses to allow additional servers. However, Akamai has tens of thousands of edge servers and cannot provide a list of all IP addresses on the Akamai Network.
The actual IP addresses on the Akamai Network are subject to change at any time and distributing an authoritative list of current Akamai IP addresses is administratively prohibitive. One of the features of the Akamai Network is that even when machines become unavailable, Akamai is able to dynamically map users to the closest available server. Hence, hard coding the Akamai IP addresses into any system is not recommended.
Note that a firewall with an IP ACL policy has the additional disadvantage that IP addresses can easily be spoofed from an illegitimate source. Akamai recommends that network administrators using IP ACLs employ a simple proxy server that filters traffic based on domain name in the HTTP request, rather than by the IP address of the remote server.