Libraries may enter their own IP's in LibCentral under Settings>System>IP Restrictions. >See more 

A library may also send IP ranges to Ebook Support and we will enter them into your Ebook Central account. However, when submitting IP range updates to Ebook Support for your Ebook Central account, we request that you provide the IP's as a range for quicker turnaround.

Example IP range:

This may also be expressed with CIDR notation, but please note this may lead to delays given each entry will need to be converted to the full IP range before adding it to the account.

Example IP with CIDR notation: