"TCP/IP Detailed Volume 1: Protocol" 12th chapter broadcast and multicast---reading notes

"TCP/IP Detailed Volume 1: Protocol" 12th chapter broadcast and multicast---reading notes

1. Introduction

Broadcast and multicast are used only for UDP, and they are important for applications that need to transmit messages to multiple recipients simultaneously.

Sometimes, a host sends frames to all other hosts on the web, which is the broadcast.

Multicast (multicast) is between unicast and broadcast: frames are routed only to multiple hosts that belong to a multicast group.

2. Broadcasting

2.1. Restricted broadcasts

The restricted broadcast address is 255.255.255.255. This address is used for the destination address of the IP datagram during host configuration, at which point the host may not know the network mask of its network or even its IP address.

In any case, the router does not forward datagrams with the destination address being a restricted broadcast address, and such data only appears on the local network.

2.2, the broadcast to the network

The broadcast address that points to the network is the address with the host number 1.

The Class A network broadcast address is netid.255.255.255, where NetID is the network number of the Class A network.

A router must forward a broadcast that points to a network, but it must also have a choice not to forward.

2.3. Broadcast to Subnet

The broadcast address to the subnet is an address with a host number of 1 and a specific subnet number.

The IP address that is the subnet's direct broadcast address requires an understanding of the subnet's mask.

2.4. Broadcast to all subnets

Broadcasts that point to all subnets also need to know the subnet mask of the destination network so that it is separate from the broadcast address that points to the network. The subnet number and the host number of the broadcast address pointing to all subnets are all 1.

3. Examples of broadcasting

4. Multicast

IP multicasting provides two types of services:

A. Transfer data to multiple destination addresses.

B. Customer requests to the server.

4.1. Multicast group Address

Figure 12-2 shows the format of the Class D IP address.

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Unlike other three-class IP addresses (A, B, and C), the assigned 28bit is used as a multicast number and no longer represents the other.

The multicast group address includes a maximum of 4bit and a multicast group number of 1110. They can usually represent dotted decimal numbers, ranging from 224.0.0.0 to 239.255.255.255.

A collection of hosts that can receive data destined for a specific multicast group address is called a host group.

A host group can span multiple networks.

A member of a host group can join or leave a cluster at any time.

There is no limit to the number of hosts in the host group, and hosts that are not part of a host group can send messages to the groups.

4.2. Conversion of multicast group address to Ethernet address

The IANA has an Ethernet address block, that is, the high 24bit is 00:00:5e (hexadecimal), which means that the address block has a range of addresses from00:00:5e:00:00:00 To00:00:5e:ff:ff:ff 。 The IANA assigns the generic as a multicast address. In order to indicate a multicast address, the first byte of any Ethernet address must be 01, which means that the Ethernet address range that corresponds to the IP multicast on: 00:5e:00:00:00 To on: 00:5e:7f:ff:ff 。

This address assignment will allow the 23bit in the Ethernet multicast address to correspond to the IP multicast group number, as shown in procedure 12-3, by mapping the low 23bit in the multicast group number to the lower 23bit implementation in the Ethernet address.

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Since address mapping is not unique, the device driver or IP layer must filter the data. Because the NIC may receive multicast data frames that the host does not want to receive. In addition, if the NIC does not provide enough multicast data filtering, the device driver must receive all multicast data frames and then filter them.

Recently in the graduation design, just use the knowledge of multicast. Good reading!

This article is from the "Do Your best" blog, so be sure to keep this source http://qiaopeng688.blog.51cto.com/3572484/1886377

"TCP/IP Detailed Volume 1: Protocol" 12th chapter broadcast and multicast---reading notes