IGMP Snooping / Proxy / Server 組員：邱鑫坤925650 劉文雄935603 郭大豪935655 劉得源935635 蔡子健935652 邱顯忠935639
IGMP Snooping IGMP Snooping的機制︰
在一些特定的網路拓撲下，不營運組播路由協議，只要學習到組播成員，依據登記的訊息進行簡單組播轉發就可以實現組播分發。這種技術稱為IGMP proxy組播代理。 其實現的原理是主機界面（又稱為上行界面）指向樹的根節點，即上聯到組播路由器。在這個界面上，營運主機功能，不營運IGMP。當接收到IGMP查詢封包時，路由器在主機端口發送IGMP成員報告，當成員資料庫發生改變時，主動發送離開或者加入組播的資料封包到相連的路由器。主機界面還要根據成員資料庫，轉發接收到組播包。路由器界面（又稱為下行界面）背離根節點，下聯用戶主機。在此端口運作IGMP協議，進行下聯用戶的組成員登記查詢刪除工作，維護成員數據庫。實現接收成員報告，建立和修改一個成員表；發送查詢包，查詢主機是否離開曾經加入的組；依據登記的組播成員的資料庫向上行和下行轉發接收到的組播數據包。
IGMP Snooping A layer-2 switch supported IGMP snooping can passively snoop on IGMP Query, Report and Leave (IGMP version 2) packets transferred between IP Multicast Routers/Switches and IP Multicast hosts to learn the IP Multicast group membership. It checks IGMP packets passing through it, picks out the group registration information, and configures multicasting accordingly. Without IGMP snooping, multicast traffic is treated in the same manner as broadcast traffic, that is , it is forwarded to all ports. With IGMP snooping, multicast traffic of a group is only forwarded to ports that have members of that group. IGMP Snooping generates no additional network traffic, allowing you to significantly reduce multicast traffic passing through your switch.
IGMP Proxy IGMP proxy enables the system to issue IGMP host messages on behalf of hosts that the system discovered through standard IGMP interfaces. The system acts as a proxy for its hosts. IGMP Proxy與IGMP Snooping建置功能相同但原理卻不同︰IGMP snooping只是透過監聽IGMP的消息來獲取有關訊息，而IGMP Proxy則攔截了終端用戶的IGMP請求並進行相關處理後，再將它轉發給上層路由器。
The IGMP Proxy mechanism was added to the Unidirectional Link Routing feature to permit hosts that are not directly connected to a downstream router to be able to join a multicast group sourced from an upstream network.
Figure 1 IGMP Mroute Proxy Mechanism
IGMP Server IGMP server-- A multicasting server 屬於layer 3的功能 不同於IGMP Proxy之request訊號不會終結而透通過去，IGMP Server對於request會終結。 其頻寬需求為頻道數＊頻道頻寬