Pim-Ssm Overview - HP A8800 Configuration Manual

Figure 47 Group address range relationship between admin-scoped zones and the global-scoped zone
Admin-scope 1
G1 address
Global-scope
−
G G1
In Figure
intersection, whereas the group address range of admin-scoped 3 is a subset of the address range
of admin-scoped 1. The group address range of the global-scoped zone covers all the group
addresses other than those of all the admin-scoped zones. That is, the group address range of the
global-scoped zone is G-G1-G2. In other words, there is a supplementary relationship between
the global-scoped zone and all the admin-scoped zones in terms of group address ranges.
Relationships between admin-scoped zones and the global-scoped zone are as follows:
The global-scoped zone and each admin-scoped zone have their own C-RPs and BSR. These
devices are effective only in their respective admin-scoped zones. Namely, the BSR election and
RP election are implemented independently within each admin-scoped zone.
Each admin-scoped zone has its own boundary. The multicast information (such as C-RP-Adv
messages and BSR bootstrap messages) can be transmitted only within the domain.
Likewise, the multicast information in the global-scoped zone cannot enter any admin-cope
region.
In terms of multicast information propagation, admin-scoped zones are independent of one
another and each admin-scoped zone is independent of the global-scoped zone, and no
overlapping is allowed between any two admin-scoped zones.

PIM-SSM overview

The source-specific multicast (SSM) model and the any-source multicast (ASM) model are two opposite
models. Presently, the ASM model includes the PIM-DM and PIM-SM modes. The SSM model can be
implemented by leveraging part of the PIM-SM technique, and it is also called PIM-SSM.
The SSM model provides a solution for source-specific multicast. It maintains the relationships between
hosts and routers through IGMPv3.
In actual application, part of IGMPv3 or PIM-SM technique is adopted to implement the SSM model. In
the SSM model, receivers know exactly where a multicast source is located by means of advertisements,
consultancy, and so on. Therefore, no RP is needed, no RPT is required, there is no source registration
process, and there is no need of using the multicast source discovery protocol (MSDP) for discovering
sources in other PIM domains.
In PIM-SSM, the "channel" concept is used to refer to a multicast group, and the "channel subscription"
concept is used to refer to a join message.
The operating mechanism of PIM-SSM is summarized as follows:
• Neighbor discovery
Admin-scope 3
G3 address
−
G2 address
47, the group address ranges of admin-scoped 1 and admin-scoped 2 have no
Admin-scope 2
G2 address
124