TCP/IP 详解 卷1 ch13 IGMP: Internet Group Management Protocol

1. IGMP报文

An IGMP type of 1 is a query sent by a multicast router, and 2 is a response sent by a host. The group address is a class D IP address. In a query the group address is set to 0, and in a report it contains the group address being reported.

1) for query

TTL = 1

IGMP组地址 = 0

目的IP地址=224.0.0.1 <= All-Hosts Group

源IP地址=路由器IP地址

2) for report

TTL = 1

IGMP组地址 = 组地址

目的IP地址=组地址

源IP地址=主机IP地址

2. a multicast router doesn't even care which host belongs to a group. It only needs to know that at least one host belongs to a group on a given interface.

3. 一个多播的例子(代码在前一章)

client join group, dest ip is "224.0.0.22
Internet Group Management Protocol
(IGMP) Version 3", refer to http://en.wikipedia.org/wiki/Multicast_address


server send msg, dest is the real group address, 224.1.1.1