A system to dynamically protect access to a first network receives a data unit containing a source address indicating a source of the data unit. The source address is matched with information stored in the system, and entry of the data unit to the first network is enabled or denied based on the matching. It is determined whether the data unit contains an identifier of a codec type that matches a stored codec type, and occurrence of an attack of the first network is indicated in response to determining that the identifier is of a codec type that does not match the stored codec type.