Here's a basic example of configuring Loop-Free Alternate (LFA) backup in Junos OS for fast reroute in case of a link or node failure. This example assumes you're working with ISIS, but similar logic applies to OSPF as well.

labroot@labrouter> show configuration protocols isis interface ae21.0                                      
apply-groups ISIS_LDP_L1_INTERFACE_GROUP;
level 1 {
    metric 50;
    ipv6-unicast-metric 50;
}
link-protection;                                                 

labroot@labrouter> show isis interface ae21.0 detail      
IS-IS interface database:
ae21.0
  Index: 75, State: 0x6, Circuit id: 0x1, Circuit type: 1
  LSP interval: 100 ms, CSNP interval: 30 s
  Adjacency advertisement: Advertise, Layer2-map: Disabled
  Protection Type: Link                                                          
  Level Adjacencies Priority   Metric Hello (s) Hold (s) Designated Router
    1             1       64       50     1.000        3
            0       64       10 Disabled   

labroot@labrouter> show isis route 150.181.X.XX 
 IS-IS routing table             Current version: L1: 1592 L2: 4
IPv4/IPv6 Routes
----------------
Prefix             L Version   Metric Type Interface       NH   Via                 Backup Score
150.181.X.XX/32    1    1592    65050 int  ae21.0          IPV4 h20-28             
                                           ae2.20          IPV4 h20-29     

labroot@labrouter> show isis backup spf results h20-28.00 
 IS-IS level 1 SPF results:
h20-28.00
  Primary next-hop: ae21.0, IPV4, h20-28, SNPA:  c:81:26:a3:42:41
  Primary next-hop: ae21.0, IPV6, h20-28, SNPA:  c:81:26:a3:42:41
    Root: h20-28, Root Metric: 50, Metric: 0, Root Preference: 0x0
      Not eligible, IPV4, Reason: Primary next-hop link fate sharing 
      Not eligible, IPV6, Reason: Primary next-hop link fate sharing 
    Root: h20-29, Root Metric: 90, Metric: 52, Root Preference: 0x0
      track-item: h20-28.00-00
      Eligible, Backup next-hop: ae2.20, IPV4, h20-29, SNPA:  c:59:9c:23:16:c5,Prefixes: 2506
      Eligible, Backup next-hop: ae2.20, IPV6, h20-29, SNPA:  c:59:9c:23:16:c5,Prefixes: 2504
...  

labroot@labrouter> show route 150.181.X.XX 

inet.0: 1004950 destinations, 2516692 routes (1004799 active, 1 holddown, 152 hidden)
@ = Routing Use Only, # = Forwarding Use Only
+ = Active Route, - = Last Active, * = Both

150.181.X.XX/32    @[IS-IS/18] 17:33:40, metric 65050
                    >  to 96.34.XX.XXX via ae21.0
                       to 96.34.XX.XXX via ae2.20                                 
                    [BGP/170] 19:01:16, MED 65000, localpref 100, from 96.34.XXX.X
                      AS path: I, validation-state: unverified
                    >  to 96.34.XX.XXX via ae21.0
                       to 96.34.XX.XXX via ae2.20, Push 687842
                   #[LDP/9] 17:33:40, metric 65050
                    >  to 96.34.XX.XXX via ae21.0, Push 604523
                       to 96.34.XX.XXX via ae2.20, Push 760517
...

labroot@labrouter> show route forwarding-table destination 150.181.X.XX/32 extensive
Routing table: default.inet [Index 0]
Internet:
   
Destination:  150.181.X.XX/32
  Route type: user                 
  Route reference: 0                   Route interface-index: 0  
  Multicast RPF nh index: 0            
  P2mpidx: 0             
  Flags: sent to PFE, rt nh decoupled 
  Next-hop type: unilist               Index: 2097180  Reference: 2   
  Nexthop: 96.34.XX.XXX
  Next-hop type: Push 604523           Index: 435827   Reference: 2   
  Load Balance Label: None             
  Next-hop interface: ae21.0        Weight: 0x1 
  Nexthop: 96.34.XX.XXX
  Next-hop type: Push 760517           Index: 427874   Reference: 2   
  Load Balance Label: None             
  Next-hop interface: ae2.20        Weight: 0xf000