Packet switching apparatus, method of transmitting multicast packet at packet switching apparatus, and setup method of packet switching apparatus

A packet switching apparatus comprising:

• n (an integer of 3 or more) slots capable of housing line interface cards to each of which an input line and an output line are connected;
• and
• a packet switch for switching packets outputted from k line interface cards housed in k (an integer equal to or greater than 2 and less than or equal to n) slots of the n slots, wherein:
• each of the k line interface cards adds a bitmap to a multicast packet inputted from the input line and outputs the multicast packet to the packet switch;
• the packet switch multicasts the multicast packets to plural line interface cards of the k line interface cards specified in the bitmap;
• and
• the length of the bitmap is made variable depending on the value of k, and wherein each of the k line interface cards brings the length of bitmap to n bits when k=n, and makes the length of the bitmap smaller than n bits when k<n.