Cisco NCS 6000 Series Configuration Manual page 155

Implementing BFD
Time (T): Echo#1 TX (count = 1)
T + 50 ms: Echo#2 TX (count = 2)
T + 100 ms: Echo#3 TX (count = 3)
T + 150 ms: Echo#4 TX (count = 4 -> echo failure
Example 3
The following example shows an example of how roundtrip latency can build beyond (I x M) for any particular
echo packet over the course of a BFD session using the standard echo failure detection, but latency between
return of echo packets overall in the session never exceeds the (I x M) window and the counter never exceeds
the multiplier, so the neighbor is not declared down.
Note You can configure BFD to detect roundtrip latency on non-bundle interfaces using the echo latency detect
command beginning.
Time (T): Echo#1 TX (count = 1)
T + 1 ms: Echo#1 RX (count = 0)
T + 50 ms: Echo#2 TX (count = 1)
T + 51 ms: Echo#2 RX (count = 0)
T + 100 ms: Echo#3 TX (count = 1)
T + 150 ms: Echo#4 TX (count = 2)
T + 151 ms: Echo#3 RX (count = 0; ~50 ms roundtrip latency)
T + 200 ms: Echo#5 TX (count = 1)
T + 250 ms: Echo#6 TX (count = 2)
T + 251 ms: Echo#4 RX (count = 0; ~100 ms roundtrip latency)
T + 300 ms: Echo#7 TX (count = 1)
T + 350 ms: Echo#8 TX (count = 2)
T + 351 ms: Echo#5 RX (count = 0; ~150 ms roundtrip latency)
T + 451 ms: Echo#6 RX (count = 0; ~200 ms roundtrip latency; no failure detection)
T + 501 ms: Echo#7 RX (count = 0; ~200 ms roundtrip latency; no failure detection)
T + 551 ms: Echo#8 RX (count = 0; ~200 ms roundtrip latency; no failure detection)
Looking at the delay between receipt of echo packets for the BFD session, observe that no latency is beyond
the (I x M) window:
Echo#1 RX – Echo#2 RX: 50 ms
Echo#2 RX – Echo#3 RX: 100ms
Echo#3 RX - Echo#4 RX: 100ms
Echo#4 RX - Echo#5 RX: 100ms
Echo#5 RX - Echo#6 RX: 100ms
Echo#6 RX - Echo#7 RX: 50ms
Echo#7 RX - Echo#8 RX: 50ms
Summary of Packet Intervals and Failure Detection Times for BFD on Bundle Interfaces
For BFD on bundle interfaces, with a session interval I and a multiplier M, these packet intervals and failure
detection times apply for BFD asynchronous mode
Time Examples on Bundle
• Value of I—Minimum period between sending of BFD control packets.
• Value of I x M
Summary of Packet Intervals and Failure Detection Times for BFD on Bundle Interfaces
Interfaces):
• BFD control packet failure detection time.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
(Table 4: BFD Packet Intervals and Failure Detection
133