A method of operating a first host within a network of a plurality of hosts. Over the course of a first time interval, requests received at the first host from a second host to send data to destination hosts are monitored. Identities of destination hosts monitored during the first time interval are compared with destination host identities in a record. Then, either data relating to requests which identify a destination host not in the record are stored in a storage buffer. Or the passage of data from the second host to the destination host within the network is limited over the course of the first time interval, so that during the first time interval the second host is unable to send data to more than a predetermined number of hosts not in the record.