ZXR10 5900E Series Configuration Guide (IPv6)
The BSR is responsible for collecting the candidate RP information on the multicast
switches in group to find out candidate RPs in the multicast domain.
It notifies the
candidate RPs to all the PIM switches in the PIM domain in a unified way. Each PIM
switch, according to the similar Hash rules, elects the one with the highest priority as the
formal RP from the same candidate RP set. Candidate RPs are configured manually.
The switches running PIM-SM discover each other and maintain the neighbor relationship
by exchanging Hello messages. In the multi-access network, the Hello messages also
contain the priority information of switches. The DR is elected according to this parameter.
The multicast source or the first hop switch (the DR connecting to the source directly)
encapsulates a packet in a Register message, and then sends it to the RP through a unicast
switch. When receiving the Register message, the RP de-encapsulates the messages to
take out the packet, and then sends the packet to the receivers of the group along the
shared multicast tree.
Each host acting as a receiver joins the multicast group through the IGMP member report
message. The last hop switch (or the DP in the multi-access network) sends the received
Join message to the RP level by level. After receiving the Join message, the intermediate
switch checks whether it has already had the routes of the group. If it has, the intermediate
switch adds the downstream request switch to the shared multicast tree as a branch. If
not, it continues to send the Join message to the RP.
When the RP or the multicast switch connects to a receiver directly, it can switch to the
SPT from the shared tree. When the RP receives a Register message sent from a new
multicast source, the RP will return a Join message to the DR directly connecting to the
multicast source. Thus, the SPT from the source to the RP is constructed.
After a DR or a switch directly connecting to multicast members receives the first multicast
packet from the multicast group, or the received packets reaches a threshold, it can switch
to the SPT from the shared tree. Once the handover occurs, the switch will send a Prune
message to the upstream neighbor and request to leave the shared tree.
In PIM-SM, there are the following types of messages.
l
Hello message: The switch interfaces on which PIM-SM runs send Hello messages
periodically to the neighbor interfaces in the same segment to establish neighbor
relationship. Hello messages are also used for switches running MLD to elect the
DR.
l
Register message: When receiving a multicast packet sent by a host in the local
network, the DR will encapsulate the packet in a Register message and send it to the
RP through unicast. The source address in the IP header of the Register message is
the address of the DR, and the destination address is the address of the RP.
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Register-Stop message: The RP unicasts a Register-Stop message to the sender of
the Register message to inform it stop sending Register messages.
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Join/Prune message: This message is forwarded in the direction to the source or
the RP. A Join message is used to construct a source tree or a shard tree. When a
receiver leaves a group, it sends a Prune message to prune the source tree or the
shard tree. This message contains the joining information and pruning information
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SJ-20150114102049-011|2015-01-15 (R1.0)
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