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Chapter 3: Configuring PIM for IPv4 Multicast
seconds before switching to the default MDT. When the timer expires, the data MDT is
deleted and the C-SG flow switched back to the default MDT if the flow rate drops back
below the threshold. If the flow rate exceeds the threshold, the timer restarts. If the timer
expires and the flow rate is below the threshold, the data MDT is removed.
The Source C-PIM-SM maintains sent MDT Join TLV messages in its database as long
as they are active. While the data MDT is active, C-PIM-SM resends that MLD Join TLV
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.
Copyright © 2010, Juniper Networks, Inc.
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