A packet routing arrangement, when receiving a request to join or leave a multicast group from a host unregistered to that group, a response is sent exclusively to the unregistered host. In the packet routing arrangement, when receiving a request packet from a host to join or leave a group, including the identifier of the group, it is determined whether the source host of the packet is registered to that group; and, if it is not registered, the first group identifier is changed to a second group identifier assigned to another delivery server delivering information to the other unregistered host and the packet is transferred to this other delivery server. When receiving a packet containing certain information from this delivery server, the second group identifier included in the received packet is changed to the first group identifier and the packet is transmitted to the unregistered host.