1. A method of managing labels for a multicast group that includes one or more label clusters, where each entry in a label cluster comprises a label for insertion into a respective packet in a multicast transmission and a validity field, the method comprising, in a processor performing the following: establishing a root table which defines the number of replications of the packet in a multicast group and identifies a first label cluster associated with the multicast group; associating with each label cluster a next cluster pointer that points to another label cluster; and establishing a sentinel cluster of which all entries are indicated to be invalid and with a next cluster pointer pointing to the sentinel cluster.