Configuring IGMP
Fixed Switch Configuration Guide 19-15
Configuring IGMP
On the fixed switch stackable and standalone devices, IGMP can be configured independently at
the switch level (Layer 2) for IGMP snooping. On fixed switch devices that support basic routing,
IGMP can also be configured at the router level (Layer 3) for determining host membership on
directly attached subnets. At Layer 2, IGMP can be enabled for VLANs, regardless of whether it is
enabled on routed interfaces. If, however, IGMP is enabled on a routed interface, and the routed
interface is a routed VLAN, then IGMP must also be enabled at the switch level.
Table 19-3 on page 19-16 lists the Layer 2 IGMP configuration commands for fixed switch devices.
Rendezvous Point (RP) The root of a group-specific distribution tree whose branches extend to all
nodes in the PIM domain that want to receive traffic sent to the group.
RPs provide a place for receivers and senders to meet. Senders use RPs to
announce their existence, and receivers use RPs to learn about new senders of
a group.
The RP router, for the group, is selected by using the hash algorithm defined in
RFC 2362.
Candidate Rendezvous
Point (Candidate-RP)
PIM routers configured to participate as RPs for some or all groups.
C-RPs send C-RP Advertisement messages to the BSR. The messages contain
the list of group prefixes for which the C-RP is willing to be the RP. Once the
PIM-SM routers receive the BSR’s message, the routers use a common
hashing algorithm to hash the C-RP address, group, and mask together to
identify which router will be the RP for a given group.
A C-RP router must also learn which PIM-SM router is the BSR. Each
designated candidate-BSR (C-BSR) asserts itself as the BSR, then defers once
it receives a preferable BSR message. Eventually, all C-RPs send their
messages to a single BSR, which communicates the Candidate RP-set to all
PIM-SM routers in the domain.
Static RP If a BSR is not used to distribute RP set information, RP-to-group mappings are
configured statically on each router.
Static RP configuration and use of bootstrap routers are mutually exclusive. You
should not configure both in a PIM-SM domain because such configuration
could result in inconsistent RP sets. Statically configured RP set information will
take precedence over RP set information learned from a BSR.
Designated Router (DR) A designated router is elected from all the PIM routers on a shared network.
DRs are responsible for encapsulating multicast data from local sources into
PIM-SM register messages and for unicasting them to the RP. The router with
the highest priority wins the DR election. In the case of a tie, the router with the
highest IP address wins.
PIM Domain A contiguous set of routers that implement PIM and are configured to operate
within a common boundary defined by PIM multicast border routers.
PIM Multicast Border
Router (PMBR)
A router that connects a PIM domain to other multicast routing domains.
sparse mode PIM sparse mode (SM) uses a host-initiated process to build and maintain the
multicast distribution tree, using only those routers that need to be included in
forwarding multicast data. Sparse mode routers use bandwidth more efficiently
than other modes, but can require more processing time when working with
large numbers of streams
Table 19-2 PIM Terms and Definitions (continued)
Term Definition
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