This article describes the issue of the configured BFD minimum interval not being shown in the output of show bfd session .
After changing the minimum-interval on one end of the BFD session (MX-240) from 1000 to 500, in the output of show bfd sessions , the value is shown as 1000. The other end (MX-80) is still configured with 1000.
|MX240|--------------------------|MX80 | | |xe-1/3/0 xe-0/0/0| | <---ospf & BFD session---->
MX240# show | compare [edit protocols ospf area 0.0.0.0 interface xe-1/3/0.0 bfd-liveness-detection] - minimum-interval 1000; + minimum-interval 500; -------------------------------------------------- MX240# run show bfd session Detect Transmit Address State Interface Time Interval Multiplier 110.44.176.1 Up 15.000 5.000 3 110.44.176.29 Up xe-1/3/0.0 3.000 1.000<----- 3 2 sessions, 2 clients Cumulative transmit rate 1.2 pps, cumulative receive rate 1.2 pps {MASTER}[edit] MX240# run show bfd session extensive Detect Transmit Address State Interface Time Interval Multiplier 110.44.176.1 Up 15.000 5.000 3 Client BGP, TX interval 5.000, RX interval 5.000 Session up time 00:50:53 Local diagnostic NbrSignal, remote diagnostic None Remote state Up, version 1 Min async interval 5.000, min slow interval 5.000 Adaptive async TX interval 5.000, RX interval 5.000 Local min TX interval 5.000, minimum RX interval 5.000, multiplier 3 Remote min TX interval 5.000, min RX interval 5.000, multiplier 3 Local discriminator 2, remote discriminator 40 Echo mode disabled/inactive Multi-hop, min-recv-TTL 0, route table 0, local-address 110.44.176.2 Detect Transmit Address State Interface Time Interval Multiplier 110.44.176.29 Up xe-1/3/0.0 3.000 1.000<----- 3 Client OSPF realm ospf-v2 Area 0.0.0.0, TX interval 0.500, RX interval 0.500 Session up time 03:05:32 Local diagnostic None, remote diagnostic None Remote state Up, version 1 Min async interval 0.500, min slow interval 1.000 Adaptive async TX interval 0.500, RX interval 0.500 Local min TX interval 0.500, minimum RX interval 0.500, multiplier 3 Remote min TX interval 1.000, min RX interval 1.000, multiplier 3 Local discriminator 1, remote discriminator 39 Echo mode disabled/inactive Remote is control-plane independent
This is expected behavior and it is not a software bug. As per RFC 5880 , a system must not transmit BFD Control packets at an interval, which is less than the larger value out of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval . The transmit interval must be re-calculated, whenever bfd.DesiredMinTxInterval or bfd.RemoteMinRxInterval changes and is equal to the greater of these two values. When you have the interval configured as 500 on one side and 1000 on the other, the larger value is selected from the two and 1000 is seen as the transmit interval; even when the configured value is 500.