The answer given seems a little thin. Here's how I understand this to work. When a router wants to join (*, G), it either needs to know the IP of the rendezvous point (RP) or a source generating the mulitcast traffic. Until the tree to the RP is built, the router only knows about the RP IP address. Thus, when the router wants to join (*, G), it does a routing loopkup for the RP IP address. The interface that would be used to reach the RP IP address is marked as the *incoming* interface, and then the router sends a JOIN (*, G) out this interface. This recursively happens, one router at a time, until the JOIN reaches the RP.
If there's s source generating traffic, and once the tree to the RP is built, the router will start to receive multicast traffic. The router will therefore know a source for the multicast traffic, and could then, if so configured, build a tree to the source. The difference is now the router uses the source IP in its lookup into the routing table. The interface returned is now the incoming interface for the source and the interface over which the (S, G) JOIN is sent. Thus, using the source IP, the tree grows back to the source forming the SPT. The routing table referenced, when using PIM, can be the unicast routing table. However, if there's a need to apply policy unique to the multicast traffic (ie which paths to use to get to the RP or source IP), a second routing table can be referenced. This is the "mroute" table. Information typically inserted into this routing table is via static routes or MBGP (multicast BGP). In order to build the tree to the RP, the router must know the RP IP address. There are a number of ways for the router to become aware of the RP IP address. The first is for this information to be statically configured. Other approaches include the use of PIM's bootstrap message mechanism. A third approach is cisco's "auto-RP" approach. Antero Vasconcelos wrote: > > question > > In a PIMv2 Sparse Mode network, the "incoming interface" for a > (*, G) mroute > entry is calculated using: > > answer > > The address of a directory connected member of group "G". > > anybody can explaim this answer. > > I4ve looked in the Books and still don4t undestand the question > neither the > answer!!!!!! > > > thx in adv > > Antero > > > > *************************************************************************** > Este email assim como os ficheiros que possa ter em anexo sao > confidenciais e para uso exclusivo da pessoa ou organizacao > para o qual foi enviado. Se recebeu esta mensagem por engano > por favor notifique a Compta atraves do endereco > [EMAIL PROTECTED] > > Esta mensagem foi verificada pelo sistema MAILsweeper nao tendo > sido encontrados virus. http://www.mimesweeper.com > > MAILsweeper - Modulo da suite MIMEsweeper, solucao de filtragem > de conteudos comercializada pela Compta SA. > > A Compta SA detem o mais alto nivel de especializacao > MIMEsweeper, tendo sido reconhecida pela Clearswift como > Premier Partner. > *************************************************************************** > This message is confidential and may contain privileged > information intended solely for the named addressee(s). It may > not be used or disclosed except for the purpose for which it > has been sent. > > If you are not the intended recipient, you must not copy, > distribute or take any action in reliance on it. If you have > received this message in error, please notify Compta by > emailing [EMAIL PROTECTED] quoting the sender and delete the > message and any attached documents. > > This footnote confirms that this email message has been swept > by MIMEsweeper for Content Security threats, including computer > viruses > *************************************************************************** > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=73162&t=73158 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
