A method of dynamic routing with link aggregation across intermediary devices (200a-n) of a cluster, wherein at least a first intermediary device (200a, 200b) of the cluster of intermediary devices (200a-n) has an external network connection; the method comprising: a) establishing, for each intermediary device (200a-n) in the cluster of intermediary devices (200a-n), a special Media Access Control, MAC, identifier, the special MAC identifier of each intermediary device (200a-n) in the cluster comprising a cluster identifier identifying the cluster and a node identifier identifying that intermediary device (200a-n) of the cluster; b) receiving, by the first intermediary device (200a, 200b) of the cluster, a multicast routing packet from a router via a connection of an established link aggregation group; c) inserting, by the first intermediary device (200a, 200b), the special MAC identifier of the first intermediary device (200a, 200b) as a source MAC identifier of the multicast routing packet; d) forwarding, by the first intermediary device (200a, 200b) to each of the other intermediary devices (200c-n) of the link aggregation group, the multicast routing packet having the special MAC identifier of the first intermediary device (200a, 200b) inserted as its source MAC identifier; e) identifying, by a second intermediary device (200c-n) of the link aggregation group, the special MAC identifier of the first intermediary device (200a, 200b) inserted as the source MAC identifier of the forwarded multicast routing packet; and f) determining, by the second intermediary device (200c-n) responsive to the identification, that the multicast routing packet was forwarded by another intermediary device (200a, 200b) of the link aggregation group and not forwarding, by the second intermediary device (200c-n), the multicast routing packet responsive to the determination. a) establishing, for each intermediary device (200a-n) in the cluster of intermediary devices (200a-n), a special Media Access Control, MAC, identifier, the special MAC identifier of each intermediary device (200a-n) in the cluster comprising a cluster identifier identifying the cluster and a node identifier identifying that intermediary device (200a-n) of the cluster; b) receiving, by the first intermediary device (200a, 200b) of the cluster, a multicast routing packet from a router via a connection of an established link aggregation group; c) inserting, by the first intermediary device (200a, 200b), the special MAC identifier of the first intermediary device (200a, 200b) as a source MAC identifier of the multicast routing packet; d) forwarding, by the first intermediary device (200a, 200b) to each of the other intermediary devices (200c-n) of the link aggregation group, the multicast routing packet having the special MAC identifier of the first intermediary device (200a, 200b) inserted as its source MAC identifier; e) identifying, by a second intermediary device (200c-n) of the link aggregation group, the special MAC identifier of the first intermediary device (200a, 200b) inserted as the source MAC identifier of the forwarded multicast routing packet; and f) determining, by the second intermediary device (200c-n) responsive to the identification, that the multicast routing packet was forwarded by another intermediary device (200a, 200b) of the link aggregation group and not forwarding, by the second intermediary device (200c-n), the multicast routing packet responsive to the determination.