While all four types of communication methods (unicast, multicast, broadcast, and anycast) are technically allowed on the Internet, the context of what is permitted typically refers to the type of application or specific use cases rather than the communication method itself.
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Unicast: One-to-one communication, where a message is sent from one sender to one receiver. This is the most common form of communication on the Internet.
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Multicast: One-to-many communication, where a message is sent from one sender to multiple receivers who have expressed interest in receiving it. This is generally allowed, but there may be limitations based on network infrastructure or configuration.
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Broadcast: One-to-all communication, where a message is sent from one sender to all possible receivers in a network segment. While broadcast is common in local area networks (LANs), it is generally not used on the Internet as a whole because of routing limitations; routers typically do not forward broadcast traffic.
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Anycast: A one-to-nearest communication model, where a message is sent to the nearest of multiple possible receivers that share the same address. This is allowed and used in various applications, such as content delivery networks.
In summary, while unicast, multicast, and anycast are generally allowed on the Internet, broadcast communication is not typically used in Internet routing due to its nature. Therefore, if we consider which type of communication is effectively not allowed on the broader Internet, broadcast would be the answer.