Interfaces - Cisco ASR 9000 Series Routing Configuration Manual

BFD Packet Information
You can configure BFD to detect roundtrip latency on non-bundle interfaces using the echo latency detect
Note
command beginning in Cisco IOS XR 4.0.1.
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
The BFD control packet failure detection time is the maximum amount of time that can elapse without receipt
of a BFD control packet before the BFD session is declared down.
• Value of (I x M) x M—BFD echo packet failure detection time. This is the maximum amount of time
that can elapse without receipt of a BFD echo packet (using the standard multiplier counter scheme as
described in
down.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Interfaces):

◦ BFD control packet failure detection time.
◦ Minimum period between sending of BFD echo packets.
Echo Packet Failure Detection In Asynchronous
(Table 3: BFD Packet Intervals and Failure Detection
Mode) before the BFD session is declared
Implementing BFD