1. A method of managing a label data base including one or more label clusters, of which each entry in a label cluster comprises a label or data field for insertion into a respective packet in a multicast transmission and a validity field, the method comprising: in a processor, executing the acts of: (a) establishing a fixed size (N) for each of one or more label cluster, where (N) is a number of labels or data fields in each of the label clusters; (b) associating with each label cluster a pointer to another label cluster; (c) establishing a sentinel cluster of which all entries are indicated to be invalid and of which the cluster pointer points to this sentinel cluster; (d) establishing a root table which defines the number of replications of the packet in a multicast group and identifies a first cluster associated with the multicast group; and (e) establishing a chain of label clusters of which each label cluster which is full of valid entries points to the next label cluster in the chain and the last label cluster which contains valid entries points to the sentinel cluster.