Chapter 4 Configuring Bfd - Juniper IP SERVICES - CONFIGURATION GUIDE V 11.1.X Configuration Manual

Each pair of peers negotiates acceptable transmit and receive intervals for BFD
packets. These values can be different on each peer.
The negotiated transmit interval for a peer is the interval between the BFD packets
that it sends to its peers. The receive interval for a peer is the minimum time that it
requires between packets sent from its peer; the receive interval is not negotiated
between peers.
To determine the transmit interval, each peer compares its configured minimum
transmit interval with its peer's minimum receive interval. The larger of the two
numbers is accepted as the transmit interval for that peer.
Consider the following example. Router A and Router B are peers, with the following
BFD liveness detection values configured.
Configured Transmit
Router Interval (ms)
A 400
B 450
For Router A, the negotiated transmit interval is the greater of its transmit interval
(400 ms) and the Router B receive interval (450 ms), or 450 ms.
For Router B, the negotiated transmit interval is the greater of its transmit interval
(450 ms) and the Router A receive interval (500 ms), or 500 ms.
The liveness detection interval is the period a peer waits for a BFD packet from its
peer before declaring the BFD session to be down. The detection interval is
determined independently by each peer and can be different for each. The detection
interval for the local peer is calculated as the remote peer's negotiated transmit
interval times the detection multiplier value configured on the remote peer.
Negotiated Transmit
Router Interval (ms)
A 450
B 500
For Router A, the detection interval is Router B's negotiated transmit interval
times the Router B detection multiplier: 500 ms x 3 = 1500 ms.
For Router B, the detection interval is Router A's negotiated transmit interval
times the Router A detection multiplier: 450 ms x 2 = 900 ms.
If Router A fails to receive a BFD packet from Router B within 1500 milliseconds,
Router A declares the BFD session to be down. Similarly, if Router B fails to receive
a BFD packet from Router A within 900 milliseconds, Router B declares the BFD
Chapter 4: Configuring BFD
Configured Receive
Interval (ms)
500
450
Detection Liveness Detection
Multiplier Interval (ms)
2 1500
3 900
Bidirectional Forwarding Detection Overview
115