Description

This knowledge base article describes the base configuration for setting up static routes, with multihop BFD, that enables detection of faults in the bidirectional path between two BFD peers, including interfaces and data links, with potentially very low latency.

Symptoms

With multihop BFD in the following topology, it is possible to detect failures in the middle device (EX73) that impact the forwarding path of a static route and causes that route to go to be de-installed as a result.

Topology:

          ge-0/0/6           ge-0/0/7
[EX72] ===== [EX73]=====[EX74]

Solution

Add the following configurations for static route 100.200.200.0/24 on EX72 , and the return route 100.201.201.0/24 on EX74 , as well as routes for EX73 .


 
EX72:
root@EX72# show routing-options | display set
set routing-options static route 192.168.10.0/24 next-hop 192.168.20.1
set routing-options static route 100.200.200.0/24 qualified-next-hop 10.30.30.1
set routing-options static route 100.200.200.0/24 bfd-liveness-detection minimum-interval 100
set routing-options static route 100.200.200.0/24 bfd-liveness-detection neighbor 10.30.30.1
set routing-options static route 100.200.200.0/24 bfd-liveness-detection local-address 10.20.20.1
set routing-options static route 100.200.200.0/24 bfd-liveness-detection minimum-receive-ttl 1
set routing-options static route 100.200.200.0/24 resolve
set routing-options static route 10.30.30.0/24 next-hop 10.20.20.2
 
EX73:
root# show routing-options | display set
set routing-options static route 100.200.200.0/24 next-hop 10.30.30.1
set routing-options static route 100.201.201.0/24 next-hop 10.20.20.1

EX74:
root@EX74# show routing-options | display set
set routing-options static route 0.0.0.0/0 next-hop 10.3.0.1
set routing-options static route 100.201.201.0/24 qualified-next-hop 10.20.20.1
set routing-options static route 100.201.201.0/24 bfd-liveness-detection minimum-interval 100
set routing-options static route 100.201.201.0/24 bfd-liveness-detection neighbor 10.20.20.1
set routing-options static route 100.201.201.0/24 bfd-liveness-detection local-address 10.30.30.1
set routing-options static route 100.201.201.0/24 bfd-liveness-detection minimum-receive-ttl 1
set routing-options static route 100.201.201.0/24 resolve
set routing-options static route 10.20.20.0/24 next-hop 10.30.30.2


Verify that the BFD sessions are up and routes are installed on EX72 and EX74:

root@EX72# run show bfd session
Detect Transmit
Address State Interface Time Interval Multiplier
10.30.30.1 Up 0.300 0.100 3

1 sessions, 1 clients
Cumulative transmit rate 10.0 pps, cumulative receive rate 10.0 pps

root@EX74# run show bfd session
Detect Transmit
Address State Interface Time Interval Multiplier
10.20.20.1 Up 0.300 0.100 3

1 sessions, 1 clients
Cumulative transmit rate 10.0 pps, cumulative receive rate 10.0 pps

root@EX72# run show route 100.200.200.0

inet.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

100.200.200.0/24 *[Static/5] 00:03:45, metric2 0
> to 10.20.20.2 via ge-0/0/6.0

root@EX74# run show route 100.201.201.0

inet.0: 16 destinations, 16 routes (16 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

100.201.201.0/24 *[Static/5] 00:04:07, metric2 0
> to 10.30.30.2 via ge-0/0/7.0


Induce a failure on EX73:

root# show interfaces ge-0/0/7 |display set
set interfaces ge-0/0/7 disable
set interfaces ge-0/0/7 unit 0 family inet address 10.30.30.2/24

ge-0/0/7 down down
ge-0/0/7.0 up down inet 10.30.30.2/24


Verify that BFD sessions went down and static routes de-installed on EX72 and EX74:

root@EX72# run show bfd session
Detect Transmit
Address State Interface Time Interval Multiplier
10.30.30.1 Down 0.300 1.000 3

root@EX74# run show bfd session
Detect Transmit
Address State Interface Time Interval Multiplier
10.20.20.1 Down 0.300 1.000 3

root@EX72# run show route 100.200.200.0

{master:0}[edit]
root@EX72#

root@EX74# run show route 100.201.201.0

inet.0: 13 destinations, 13 routes (13 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0 *[Static/5] 3w4d 23:23:13
> to 10.3.0.1 via me0.0

{master:0}[edit]

Note that EX74 shows default route because default route was configured.

Modification History

 2021-05-10: Article reviewed for accuracy; article accurate and valid

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