Assert, Introduction to administrative scoping, Division of pim-sm domains – H3C Technologies H3C SecPath F1000-E User Manual
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abstracts the multicast data and sends the multicast data down the RPT to the DRs at the receiver side. The
RP acts as a transfer station for all multicast packets. The whole process involves three issues:
•
The DR at the source side and the RP need to implement complicated encapsulation and
de-encapsulation of multicast packets.
•
Multicast packets are delivered along a path that may not be the shortest one.
•
When the multicast traffic increases, a great burden is added to the RP, increasing the risk of failure.
To solve the issues, PIM-SM allows an RP or the DR at the receiver side to initiate an SPT switchover
process:
1.
The RP initiates an SPT switchover process
Upon receiving the first multicast packet, the RP sends an (S, G) join message hop by hop towards the
multicast source to establish an SPT between the DR at the source side and the RP. The subsequent
multicast data from the multicast source travels along the established SPT to the RP.
NOTE:
For more information about the SPT switchover initiated by the RP, see
2.
The receiver-side DR initiates an SPT switchover process
Upon receiving the first multicast packet, the receiver-side DR initiates an SPT switchover process, as
follows:
•
The receiver-side DR sends an (S, G) join message hop by hop towards the multicast source. When
the join message reaches the source-side DR, all the routers on the path have installed the (S, G)
entry in their forwarding table, and thus an SPT branch is established.
•
When the multicast packets travel to the router where the RPT and the SPT deviate, the router drops
the multicast packets received from the RPT and sends an RP-bit prune message hop by hop to the
RP. Upon receiving this prune message, the RP sends a prune message towards the multicast source
(suppose only one receiver exists). Thus, SPT switchover is completed.
•
Finally, multicast data is directly sent from the source to the receivers along the SPT.
PIM-SM builds SPTs through SPT switchover more economically than PIM-DM does through the “flood
and prune” mechanism.
Assert
PIM-SM uses a similar assert mechanism as PIM-DM does. For more information, see
Introduction to Administrative Scoping
Division of PIM-SM domains
Typically, a PIM-SM domain contains only one BSR, which is responsible for advertising RP-set
information within the entire PIM-SM domain. The information for all multicast groups is forwarded within
the network scope administered by the BSR. We call this non-scoped BSR mechanism.
To implement refined management, a PIM-SM domain can be divided into one global scope zone and
multiple administratively scoped zones (admin-scope zones). We call this administrative scoping
mechanism.
The administrative scoping mechanism effectively releases stress on the management in a single-BSR
domain and enables provision of zone-specific services using private group addresses.