message using a setting that you can configure using the mdt-interval command to
measure time in seconds between successive MLD join TLV messages.
Data MDT Receivers
When the Receiver C-PIM-SM receives a <C-SG, P-G> MDT Join TLV message from the
default MDT, it extracts the C-SG and the data MDT P-Group address from the TLV and
queries the route map that you specified for the data MDT to determine whether the
C-SG is a candidate for a data MDT. If it matches, the C-PIM-SM adds the MDT Join TLV
to its database and records the time.
If the Receiver C-PIM-SM does not receive an MDT Join TLV<C-SG, P-G> to refresh its
database within the amount of time specified for the timeout in the mdt-data-timeout
command, the MDT Join TLV<C-SG> is removed from the database and the associated
data MDT is removed.
When a new MDT Join TLV<C-SG, P-G> is added to the database, the Receiver C-PIM-SM
determines whether it has an SG, SPT state. If it has an SG state, and the incoming
interface (IIF) is the default MDT, then C-PIM-SM creates the data MDT and deletes the
corresponding forwarding entry. C-PIM-SM waits for the source to transmit data on the
data MDT. During this period, data can continue to be received on the default MDT.
C-PIM-SM fails the reverse-path forwarding (RPF) check, which results in a forwarding
entry with a discarded IIF.
If the C-SG,SPT state is created (either as a result of a C-SSM join or switch from RPT
to SPT), and it is the default MDT, the Receiver C-PIM-SM determines whether an MDT
Join TLV<C-SG> is active. If it is, C-PIM-SM creates the data MDT.
Establishing a Data MDT Using ASM or SSM
A data MDT carries one C-SG flow. If the data MDTs are established using any-source
multicast (ASM), then the P-Group address selected by a PE for the data MDT must be
unique to that PE in the MDT (that is, the range of MDT P-Group addresses available in
the core must be administratively divided among all the PEs that will source VPN
multicasts). The VRFs in a PE must share the P-Group addresses in the assigned range
for the PE.
If the data MDTs are established using single-source multicast (SSM), you must configure
VRFs to transmit on a tunnel using the same MDT P-Group address. Each VRF transmits
using a unique P-Source address; however, each data MDT created by the VRF must use
a different P-Group address. There might be one sender data MDT and possibly many
receiver data MDTs sharing an IP tunnel. Each PE can assign MDT P-Groups from the
same range, but the P-Group addresses must be administratively divided among the
VPNs.
For a receiver on the data MDT, P-PIM-SM joins the data MDT by propagating join state
into the core. The P-Group for that join is extracted from the MDT Join TLV. If SSM is not
activated or the P-Group is not in the SSM group range, P-PIM-SM performs a <*, G> join
towards the RP for that P-Group.
If SSM is activated and the P-Group is in the SSM group range, P-PIM-SM performs an
<S, G> join towards the P-Source, where the P-Source address is the SA of the MDT Join
TLV.
97Copyright © 2010, Juniper Networks, Inc.
Chapter 3: Configuring PIM for IPv4 Multicast
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