Broadcast, Multicast and Unicast

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Still under construction

Computers and network devices (routers, switches, etc.) in a network can send information packages in different ways, depending on the number of destinations.


Host (sender) (all 32 bites to set to 1)


(entirely from

Multicasting identifies logical groups of computers. A single message can then be sent to the group.

Multicasting uses the Internet Group Management Protocol (IGMP) to identify groups and group members. Routers will also use IGMP to send messages to subnets that have group members. The router actually doesn’t keep track of which hosts are members of which group, only that the subnet contains at least one member for each group. If we have multiple routers, they will communicate and exchange information about multicast groups that they have.

Each host on the network can belong to multiple multicast groups. Hosts can join or leave groups at any time. Multicast groups are identified by special IP addresses between the range of and Each group is assigned it’s own address. Addresses within the range are reserved for local subnet communications.

When we use a switch to connect hosts, multicast messages are actually forwarded to all hosts on the hub or the switch. As you should know, devices actually use MAC addresses to communicate on the local network segment. When the device on the local segment needs to send a multicast message, it will use a frame with a special MAC address. Special multicast addresses in the MAC address begin with 01-00-5E. The remaining portion of the MAC address is a modified format of the multicast IP address. When the switch receives the frame with the multicast MAC address, it will forward the frame out all ports to all connected devices. In this case, even devices that are not members of the original IP multicast group will see the frame. However, devices that don’t belong to the IP multicast group will not process the frame since they will check the destination IP address. If we want to avoid this problem in which devices which don’t belong to the original IP multicast group still receive packets, we have to implement switches that are capable of IGMP snooping. IGMP snooping feature enables switches to check which device belongs to which multicast group. In that case, when a message arrives at the switch addressed to a specific group using the special frame address, the switch will forward that frame to the individual group members. It will not forward the frame to the devices that are not a member of the group. Only the switch with IGMP snooping can do that. So, the switch controls forwarding the frames to specific group members. The router keeps track of which subnets have group members.

All info

Address:           11000110.00000100.01011110 .00111001
Netmask: = 24    **11111111.11111111.11111111 .00000000**
Wildcard:             00000000.00000000.00000000 .11111111
Network:         **11**000110.00000100.01011110 .00000000 **(Class C)**

Broadcast:          11000110.00000100.01011110 .11111111
HostMin:            11000110.00000100.01011110 .00000001
HostMax:          11000110.00000100.01011110 .11111110
Hosts/Net: 254                   

(calculations done via IP Calculator)