"TCP/IP detailed Volume One" Reading notes-----broadcast & Multicast &IGMP

1, broadcast and multicast are only applicable to UDP, because TCP is connection-oriented, you need to bind two hosts two processes, that is, IP address and port pair

2, usually, the network card can see every data frame in the net, but often it only accepts the destination address and its own MAC address of the same or broadcast address of the frame (now some can also receive a multicast address), and then transfer it to the device driver

3, broadcast the problem is that it to those who are not interested in the broadcast data host increased processing burden (need to pass the network card, driver, IP and other layers of judgment), and the emergence of multicast just solves these problems. Typically a master opportunity is assigned to join one or more multicast groups, and the NIC is told which multicast group it belongs to, so that only multicast data frames belonging to those groups are accepted, greatly reducing the overhead of processing

4. Broadcast Address type:

1) Limited broadcast:255.255.255.255, this address is used during host configuration, that is, the host may not know their own subnet mask or even IP address, as the destination address in the IP datagram, the data you want to send to each host in this network segment. It is important to note that in any case, it will not be forwarded by the router.

2) net-directed Broadcast: The host Number field for this type of address is set to 1, and the Network number field is the network address of the destination network. Each host that is used to send datagrams to a specified network

3) subnet-directed Broadcast: The host number field for such addresses is all 1, and you need to know the subnet mask of the corresponding subnet, because the subnet mask is different and may no longer be a broadcast address. Each host that is used to send data to a specified subnet

4) all-subnets-directed Broadcast: Unlike subnet-directed broadcast, the subnet field of the broadcast address is also set to 1, which means that data is sent to all subnets of the network, but it is not generally used now

5, the IP address classification of the Class D address is a multicast address, dotted decimal notation is 224.0.0.0~239.255.255.255, usually those listening to the same multicast address of the host composed of a collection called the host group. Hosts in the host group can span multiple networks, and hosts can choose to join or exit the host group at any time. Even if a host does not belong to the host group, it can send information to group.

6, similar to the well-known port in TCP/IP, the multicast address also has a well-known address for the specific service

7, the MAC address in Ethernet corresponds to the IP multicast address part of 01:00:5E:00:00:00~01:00:5E:7F:FF:FF, usually send a multicast IP datagram, enter the link layer need to determine the destination MAC address, It is common to embed the right 23 bits of the IP address into the appropriate MAC address, as shown in. As you can see, the IP address and MAC address are not one by one corresponding because the 5th to 9th bit of the IP address is indeterminate. Therefore, after the network card accepts the data frame, the device driver layer and the IP layer still need to filter operation.

8. Multicast process: The sending process sets the destination address as a multicast address, and the device driver of the source host converts it to the appropriate MAC address and sends it. The process at the receiving end needs to tell its IP layer that it wants to accept data from a multicast address, and the corresponding device driver sets up a data frame that can accept the corresponding MAC address. This completes the setup of both sides of the communication, and this process is called "joining a multicast group". Unlike UDP, typically a multicast IP datagram can be transmitted to multiple processes on the same host, as long as they are joined by the multicast group mentioned above.

9. IGMP (Internet Group Management Protocol): The purpose of this Protocol is simply to support multicast routers in order to know which ports to send multicast datagrams to, so it needs to periodically send inquiry packets from various ports, Waiting for the host to answer what multicast group they belong to, thus building an association table of ports and multicast addresses, which enables the distribution of multicast data and solves multicast problems across network segments.

10, usually the host needs to maintain a table for multicast, the contents of the table has the multicast address and the corresponding network interface (multicast address and network interface binding) and the number of processes to join the corresponding multicast. Whenever a process joins a new group, the host sends a notification from the appropriate network interface informing the multicast router and other multicast hosts, but subsequent process re-entry and any process exit will no longer be notified.

11. Address 224.0.0.1 is called the All-hosts group address, asking for the destination of the IGMP message is it. The members of its multicast group are all hosts participating in the multicast (that is, hosts that have processes participating in the multicast) and routers that belong to the physical network. The multicast address in 224.0.0.0~224.0.0.255 requires that the multicast distance cannot exceed one hop, that is, the multicast router cannot forward the multicast IP datagram for that address, even if the TTL in the datagram is not 0

"TCP/IP detailed Volume One" Reading notes-----broadcast & Multicast &IGMP