• Use to enable multicast distribution tree operation so the IP tunnel component can
create an MDT interface. This command functions for GRE interfaces only.
• Example
host1(config-if)#tunnel mdt
• The no version disables MDT on the interface.
• See tunnel mdt.
Creating Multicast VPNs Using the Data MDT
A data multicast distribution tree (MDT), based on section 8 of Internet draft
draft-rosen-vpn-mcast-08.txt, Multicast in MPLS/BGP IP VPNs, solves the problem of P
routers flooding unnecessary multicast information to PE routers that have no interested
receivers for a particular VPN multicast group. The data MDT solution requires the creation
of a new tunnel by the PE router if the source exceeds a configured rate threshold
parameter. All other PE routers join the new tunnel only if the PE router has receivers in
the VPN for that multicast group.
The JunosE Software uses dynamic point-to-multipoint GRE tunnels to configure data
MDTs. In the current release, IPv6 transport over GRE (unicast or multicast) is not
supported. For more information, see Configuring Dynamic IP Tunnels in the JunosE IP
Services Configuration Guide.
Data MDTs are established using PIM-SM (shared RP Trees) and PIM-SSM (Source
Trees). Profiles for dynamic interfaces in the VRF are restricted to sparse-mode only.
Data MDT Sources
A C-SG flow arriving in the source VRF is a candidate for a data MDT if the system matches
the C-SG in the route map that you specify for the data MDT using the ip pim data-mdt
command. The C-SG flow is initially forwarded on the default MDT. The system creates
the data MDT when the flow rate exceeds a value you configure in the route map using
the set threshold command.
When the Source C-PIM-SM first creates a data MDT for a C-SG flow, it sends a <C-SG,
P-G> MDT join message with type, length, value (TLV) format to the default MDT. This
message invites peer PE routers to join the new data MDT. It starts a timer that you can
configure using the mdt-data-delay command to track the number of seconds before
switching to the data MDT. When that timer expires, C-PIM-SM switches from sending
C-SG data on the default MDT to sending data on the data MDT.
When the C-SG flow is switched to the data MDT, the Source C-PIM-SM starts a timer
that you can configure using the mdt-data-holddown command to track the number of
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
Copyright © 2010, Juniper Networks, Inc.96
JunosE 11.2.x Multicast Routing Configuration Guide
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