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组播技术Spare-mode的注册过程详解  

2013-05-22 12:49:00|  分类: 安德的组播技术文 |  标签: |举报 |字号 订阅

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1st-hop router sends “Registers” to the RP
In PIM Sparse mode, when a 1st-hop router receives the first multicast packet from directly connected 

source “S” for group “G”, it creates (S, G) state and sets the “F” bit in the (S, G) entry to 

indicate that it is a directly connected “Source” and also sets the “Registering” flag to indicate 

that it’s in the process of “Registering”.第一跳路由器向RP发送“注册”。第一跳路由器收到直连的源的组

播报文,创建(S,G)表项,同时在该表项中设置F位表明它直连了源,同时设置注册“registering”flag表明它在注

Next, the 1st-hop router encapsulates the original multicast packet in a PIM Register message and 

unicasts it to the RP.  (Any subsequent multicast packets received from directly connected source “S” 

for group “G” are also encapsulated in a Register message and unicast to the RP.  This continues until 

an (S, G) “Register-Stop” message is received from the RP.)接下来,第一跳路由器封装原始的组播报文到PIM

注册包中,单播到RP(任意从直连的源收到的随后的组播包也被封装到注册报文单播到RP。这个过程会持续下去,直到

从RP收到一个注册停止报文)
RP receives “Register messages
When the RP receives a “Register” message it will de-encapsulated the message.  If this packet is to a 

Group for which the RP has (*, G) state, the RP will:
Forward the original packet out all interfaces in the the (*, G) entry’s “oilist”.
If it has not already done so, the RP creates (S, G) state and sends an (S, G) Join back towards the 

Source in order to join the Shortest-path Tree (SPT) to Source “S”.当Rp收到注册报文,将会解封装该报文

,如果这个报文组播组G已经包含在RP的(*,G)表项中,RP将会转发组播报文到出接口列表中的所有接口;RP会创建

(S,G)表项,向源发送(S,G)的join用以形成到源的最短路径树
!
1st-hop router receives (S, G) Join
When the 1st-hop router receives the (S, G) Join (sent hop-by-hop from the RP), it processes it normally 

by adding the interface, from which the Join was received, to the “oilist” of the existing (S, G) 

entry.  (This entry was originally created when the 1st-hop router received the first multicast packet 

from directly connected Source “S”.)  This completes the building of the Shortest-Path Tree (SPT) from 

the Source to the RP.当第一跳路由器收到来在RP的逐跳的(S,G)join,会把收到Join的接口加入到已经存在(S
,G)的出接口列表中-该(S,G)表项是连接源的第一跳设备收到第一个组播报文时就已经产生的。该过程完成之后源

到RP的最短路径树形成
The 1st-hop router now begins forwarding Source “S” multicast traffic down the newly built Shortest-

Path Tree (SPT) to the RP.第一跳设备现在向下通过新建立的最短路径树(源到RP)开始转发源的组播流
Note: (S, G) traffic temporarily flows to the RP via two methods; via Register messages (until a 

Register-Stop message is received) and the “native” Shortest-Path Tree (SPT).注意:(S,G)流量临时性

的通过下面两种方法转发到RP:通过注册报文(直到收到注册停止报文)和通过最短路径树转发的native的组播流
RP begins receiving traffic down the (S, G) SPT
As soon as the RP begins receiving (S, G) traffic “natively” (I.e. not encapsulated in Register 

messages) down the SPT, the RP will set the “T” bit in the (S, G) entry to denote that traffic is 

succesfully flowing down the Shortest-Path Tree (SPT).Now when any (S, G) Register messages are received 

by the RP, it sees that the “T” bit is set in the (S, G) entry will respond by sending a PIM (S, G) 

Register-Stop message to the 1st-hop router.  This notifies the 1st-hop router that traffic is now being 

received “natively” down the SPT.一旦RP开始收到(S,G)来的组播流量-没有封装到注册报文中,RP会设置T位

的表项表明流量成功的沿着SPT树转发过来。现在RP收到任意的来自(S,G)的注册报文,检查到T比特已经置位,将发

送一个注册停止报文给第一跳设备,用以通知第一跳路由器原始的组播流量已经通过最短路径树收到了
 1st-hop router receives “Register-Stop” message
When the (S, G) Register-Stop message is received by the 1st-hop router, it clears the “Registering” 

flag in the (S, G) entry and stops encapsulating (S,G) traffic in Register messages.  Traffic is now 

flowing only down the SPT to the RP. 第一跳路由器收到注册停止报文,将清空(S,G)的“Registering”的flag

,也停止封装(S,G)流量到注册报文中。现在流量仅仅通过最短路径树到达RP

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