This example shows how to configure a static route with multiple possible next hops. Each next hop has Bidirectional Forwarding Detection (BFD) enabled.

• Requirements
• Overview
• Configuration
• Verification

Figure 1: BFD Enabled on Qualified Next Hops

Device B

Device D

The following example requires that you navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure a static route with two possible next hops, both with BFD enabled:

If you are done configuring the devices, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

• Checking the Routing Tables
• Verifying the BFD Sessions
• Removing BFD from Device D
• Removing BFD from One Next Hop

Checking the Routing Tables

Purpose

Make sure that the static route appears in the routing table on Device B with two possible next hops.

Action

inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
192.168.47.0/24 (1 entry, 1 announced)
TSI:
KRT in-kernel 192.168.47.0/24 -> {192.168.2.2}
        *Static Preference: 5
                Next hop type: Router
                Address: 0x9334010
                Next-hop reference count: 1
                Next hop: 172.16.1.2 via ge-1/2/0.0
                Next hop: 192.168.2.2 via fe-0/1/0.2, selected
                State: <Active Int Ext>
                Age: 9 
                Task: RT
                Announcement bits (1): 3-KRT 
                AS path: I

Meaning

Both next hops are listed. The next hop 192.168.2.2 is the selected route.

Verifying the BFD Sessions

Purpose

Make sure that the BFD sessions are up.

Action

                                          Detect   Transmit
Address          State     Interface      Time     Interval  Multiplier
172.16.1.2       Up        ge-1/2/0.0     0.720     0.240        3   
192.168.2.2      Up        fe-0/1/0.2     0.720     0.240        3   

2 sessions, 2 clients
Cumulative transmit rate 8.3 pps, cumulative receive rate 8.3 pps

Meaning

The output shows that the BFD sessions are up.

Removing BFD from Device D

Purpose

Demonstrate what happens when the BFD session is down for both next hops.

Action

1. Deactivate BFD on Device D.
   [edit routing-options static route 0.0.0.0/0]user@D# deactivate bfd-liveness-detectionuser@D# commit
2. Rerun the show bfd session command on Device B.
   user@B> show bfd session

                                                     Detect   Transmit
   Address                  State     Interface      Time     Interval  Multiplier
   172.16.1.2               Down      ge-1/2/0.0     3.000     1.000        3   
   192.168.2.2              Down      fe-0/1/0.2     3.000     1.000        3   
   
   2 sessions, 2 clients
   Cumulative transmit rate 2.0 pps, cumulative receive rate 2.0 pps
   

3. Rerun the show route 192.168.47.0 command on Device B.
   user@B> show route 192.168.47.0

Meaning

As expected, when the BFD sessions are down, the static route is removed from the routing table.

Removing BFD from One Next Hop

Purpose

Demonstrate what happens when only one next hop has BFD enabled.

Action

1. If it is not already deactivated, deactivate BFD on Device D.
   [edit routing-options static route 0.0.0.0/0]user@D# deactivate bfd-liveness-detectionuser@D# commit
2. Deactivate BFD on one of the next hops on Device B.
   [edit routing-options static route 192.168.47.0/24 qualified-next-hop 172.16.1.2]user@B# deactivate bfd-liveness-detectionuser@B# commit
3. Rerun the show bfd session command on Device B.
   user@B> show bfd session

                                         Detect   Transmit
   Address      State     Interface      Time     Interval  Multiplier
   192.168.2.2   Down      fe-0/1/0.2     3.000     1.000        3   
   

4. Rerun the show route 192.168.47.0 extensive command on Device B.
   user@B> show route 192.168.47.0 extensive

   inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
   192.168.47.0/24 (1 entry, 1 announced)
   TSI:
   KRT in-kernel 192.168.47.0/24 -> {172.16.1.2}
           *Static Preference: 5
                   Next hop type: Router, Next hop index: 624
                   Address: 0x92f0178
                   Next-hop reference count: 3
                   Next hop: 172.16.1.2 via ge-1/2/0.0, selected
                   State: <Active Int Ext>
                   Age: 2:36 
                   Task: RT
                   Announcement bits (1): 3-KRT 
                   AS path: I

Meaning

As expected, the BFD session is down for the 192.168.2.2 next hop. The 172.16.1.2 next hop remains in the routing table, and the route remains active, because BFD is not a condition for this next hop to remain valid.