PIM routers send periodic hello messages from each PIM-enabled interface. You can
configure this interval using the ip pim query-interval command. By default, the PIM
router sends a hello message every 30 seconds (with an interval range of 0–210 seconds).
If it receives no response from a neighbor within 3.5 times the interval value (a minimum
of 3.5 seconds), the PIM router drops the neighbor.
In contrast, when a BFD session exists between neighbors, a PIM neighbor that goes
down is detected quickly (in milliseconds rather than in seconds).
When you issue the ip pim bfd-liveness-detection command on a PIM router, the router
establishes BFD liveness detection with all BFD-enabled PIM neighbors. When the local
router receives an update from a remote PIM neighbor—if BFD is enabled and if the session
is not already present—the local router attempts to create a BFD session to the remote
neighbor.
Each adjacent pair of neighbors negotiates an acceptable transmit interval for BFD
packets. The negotiated value can be different on each neighbor. Each neighbor then
calculates a BFD liveness detection interval. When a neighbor does not receive a BFD
packet within the detection interval, it declares the BFD session to be down.
NOTE: Before the router can use the ip pim bfd-liveness-detection command, you
must specify a BFD license key. To view an already configured license, use the show
license bfd command.
For general information about configuring and monitoring the BFD protocol, see Configuring
BFD in the JunosE IP Services Configuration Guide.
ip pim bfd-liveness-detection
• Use to enable BFD (bidirectional forwarding detection) and define BFD values to more
quickly detect PIM data path failures.
• The neighbors in a PIM network use the configured values to negotiate the actual
transmit intervals for BFD packets.
• You can use the minimum-transmit-interval keyword to specify the interval at which
the local router proposes to transmit BFD control packets to its neighbors. The default
value is 300 milliseconds.
• You can use the minimum-receive-interval keyword to specify the minimum interval
at which the local router must receive BFD control packets from its neighbors. The
default value is 300 milliseconds.
• You can use the minimum-interval keyword to specify the same value for both of
those intervals. Configuring a minimum interval has the same effect as configuring
the minimum receive interval and the minimum transmit interval to the same value.
The default value is 300 milliseconds.
• You can use the multiplier keyword to specify the detection multiplier value. The
calculated BFD liveness detection interval can be different on each neighbor. The
multiplier value is roughly equivalent to the number of packets that can be missed
before the BFD session is declared to be down. The default value is 3.
105Copyright © 2010, Juniper Networks, Inc.
Chapter 3: Configuring PIM for IPv4 Multicast
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