Multicast and Routing Guide K/KA/KB.15.15

The SPT policy should be the same
for all RPs in a domain.
Allowing some RPs to remain configured to implement SPTs
while configuring other RPs in the same domain to force RPT
use can result in unstable traffic flows. (Use the [no] ip
pim-sparse spt-threshold command to change
between SPT and RPT operation on each router.)
Application of RPs to multicast
groups.
In a PIM-SM domain, a given multicast group or range of
groups can be supported by only one RP. (Typically, multiple
C-RPs in a domain are configured with overlapping coverage
of multicast groups, but only one such candidate will be
elected to support a given group.)
Ensuring that the C-RPs in a PIM-SM
domain cover all desired multicast
groups.
All of the multicast groups you want to allow in a given
PIM-SM domain must be included in the aggregate of the
multicast groups configured in the domain's C-RPs. In most
cases, all C-RPs in a domain should be configured to support
all RP groups (the default configuration for a router enabled
as a C-RP.) This provides redundancy in case an RP becomes
unavailable. (If the C-RP supporting a particular multicast
group becomes unavailable, another C-RP is elected to
support the group as long as there is redundancy in the C-RP
configuration for multiple routers.) Note that is cases where
routers are statically configured to support a specific group
or range of groups, the C-RP prioritization mechanism allows
for redundant support.
PIM-SM and PIM-DM. These two features cannot both be enabled on the same
router at the same time.
Supporting PIM-SM across a PIM
Domain.
To properly move multicast traffic across a PIM-SM domain,
all routers in the domain must be configured to support
PIM-SM. That is, a router without PIM-SM capability blocks
routed multicast traffic in a PIM-SM domain.
Configuration steps for PIM-SM
This process assumes that the necessary VLANs and IP addressing have already been configured
on the routing switch.
NOTE: The switches described in this guide do not support PMBR operation in the current software
release.
Planning considerations
• Where multiple routers are available to operate as the DR for a given source, set the DR
priority on each router according to how you want the router used.
• Determine whether there are any bandwidth considerations that would call for disabling SPT
operation. (If any routers in the domain have SPT operation disabled, it should be disabled
on all RPs in the domain. See “Operating rules for static RPs” (page 100).)
• Determine the routers to configure as C-BSRs. In many applications, the best choice may be
to configure all routers in the domain as candidates for this function.
• Determine the multicast group support you want on each C-RP and any static RPs in the domain.
The easiest option is to enable C-RP to support all possible multicast groups on all routers in
the domain. However, if there are traffic control considerations you want to apply, you can
limit specific multicast groups to specific routers and/or set priorities so that default traffic
routes support optimum bandwidth usage.
Configuration steps for PIM-SM 101