As per https://learn.microsoft.com/en-us/azure/azure-sql/database/firewall-configure?view=azuresql
The maximum number of server-level IP firewall rules is limited to 256 for a server.
As per https://learn.microsoft.com/en-us/sql/relational-databases/system-stored-procedures/sp-set-firewall-rule-azure-sql-database?view=azuresqldb-current , a single rule can consist of a single range of consecutive IP addresses.
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hth
Marcin