TI-LFA provides supports for the following:

• Link Protection—The LFA provides repair path for failure of the link.
• Local LFA—Whenever a local LFA on the post convergence path is available, it is preferred over TI-LFA because local LFA does not require additional SID for the repair path. That is, the label for the PQ node is not needed for the release node.
• Local LFA for extended P space—For nodes in the extended P space, local LFA is still the most economical method for the repair path. In this case, TI-LFA will not be chosen.
• Tunnel to PQ intersect node—This is similar to remote LFA except that the repair path is guaranteed on the post convergence path using TI-LFA.
• Tunnel to PQ disjoint node—This capability is unique to the TI-LFA in the case when local and remote LFA cannot find a repair path.
• Tunnel to traverse multiple intersect or disjoint PQ nodes, up to the platform’s maximum supported labels—TI-LFA provides complete coverage of all prefixes.
• P2P interfaces for the protected link—TI-LFA protects P2P interfaces.
• Asymmetrical links—The ISIS metrics between the neighbors are not the same.
• Multi-homed (anycast) prefix protection—The same prefix may be originated by multiple nodes.
• Protected prefix filtering—The route-map includes or excludes a list of prefixes to be protected and the option to limit the maximum repair distance to the release node.
• Tiebreakers—A subset of existing tiebreakers, applicable to TI-LFA, is supported.

You can enable TI-LFA using any of the following two methods:

1. Protocol enablement—Enables TI-LFA in router isis mode for all IS-IS interfaces. Optionally, use the interface command to exclude the interfaces on which TI-LFA should be disabled.

   For example, to enable TI-LFA for all IS-IS interfaces:

   router isis 1
   fast-reroute per-prefix {level-1 | level-2}
   fast-reroute ti-lfa {level-1 | level-2} [maximum-metric value]

   Note	The isis fast-reroute protection level-x command enables local LFA and is required to enable TI-LFA.

2. Interface enablement—Enable TI-LFA selectively on each interface.

   interface interface-name
   isis fast-reroute protection {level-1 | level-2}
   isis fast-reroute ti-lfa protection {level-1 | level-2} [maximum-metric value]

   The maximum-metric option specifies the maximum repair distance which a node is still considered eligible as a release node.

   When both interface and protocol are TI-LFA enabled, the interface configuration takes precedence over the protocol configuration. TI-LFA is disabled by default.

   To disable TI-LFA on a particular interface, use the following command:

   interface interface-name
   isis fast-reroute ti-lfa protection level-1 disable
   

Consider the following topology to understand the configuration:

• IXIA-2 injects ISIS prefixes, and IXIA-1 sends one-way traffic to IXIA-2

  .

• In R1 10,000 prefixes are configured in the segment-routing mapping-server.

The configuration on R1 is:

configure terminal
segment-routing mpls
global-block 16 20016
!
connected-prefix-sid-map
address-family ipv4
11.11.11.11/32 index 11 range 1
exit-address-family
!
!
mapping-server
!
prefix-sid-map
address-family ipv4
120.0.0.0/24 index 2 range 1 attach
200.0.0.0/24 index 1 range 1 attach
192.168.0.0/24 index 100 range 10000 attach
exit-address-family
!
!
!
!
interface Loopback0
ip address 11.11.11.11 255.255.255.255
ip router isis ipfrr
!
interface GigabitEthernet0/1/0
ip address 14.0.0.1 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/1/2
ip address 11.0.0.1 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/1/4
ip address 200.0.0.1 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
router isis ipfrr
net 49.0001.0110.1101.1011.00
is-type level-2-only
metric-style wide
log-adjacency-changes
nsf cisco
segment-routing mpls
segment-routing prefix-sid-map advertise-local
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2
microloop avoidance rib-update-delay 10000

On R2 the configuration is

configure terminal
!
!
segment-routing mpls
!
connected-prefix-sid-map
address-family ipv4
12.12.12.12/32 index 12 range 1
exit-address-family
!
!
interface Loopback0
ip address 12.12.12.12 255.255.255.255
ip router isis ipfrr
!
interface GigabitEthernet0/1/0
ip address 12.0.0.1 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/1/1
ip address 11.0.0.2 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
router isis ipfrr
net 49.0001.0120.1201.2012.00
is-type level-2-only
metric-style wide
log-adjacency-changes
nsf cisco
segment-routing mpls
segment-routing prefix-sid-map advertise-local
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2
microloop avoidance rib-update-delay 10000
!

On R3 the configuration is

configure terminal
!
mpls traffic-eng tunnels
!
segment-routing mpls
!
connected-prefix-sid-map
address-family ipv4
13.13.13.13/32 index 13 range 1
exit-address-family
!
!
interface Loopback0
ip address 13.13.13.13 255.255.255.255
ip router isis ipfrr
!
interface GigabitEthernet0/0/4
ip address 13.0.0.1 255.255.255.0
ip router isis ipfrr
load-interval 30
speed 1000
no negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/0/5
ip address 12.0.0.2 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
router isis ipfrr
net 49.0001.0130.1301.3013.00
is-type level-2-only
metric-style wide
log-adjacency-changes
nsf cisco
segment-routing mpls
segment-routing prefix-sid-map advertise-local
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2
microloop avoidance rib-update-delay 10000
!

On R4 the configuration is:

configure terminal
!
mpls traffic-eng tunnels
!
segment-routing mpls
!
connected-prefix-sid-map
address-family ipv4
14.14.14.14/32 index 14 range 1
exit-address-family
!
!
interface Loopback0
ip address 14.14.14.14 255.255.255.255
ip router isis ipfrr
!
interface GigabitEthernet0/0/0
ip address 14.0.0.2 255.255.255.0
ip router isis ipfrr
negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/0/3
ip address 13.0.0.2 255.255.255.0
ip router isis ipfrr
speed 1000
no negotiation auto
isis network point-to-point
!
interface GigabitEthernet0/0/5
ip address 120.0.0.1 255.255.255.0
ip router isis ipfrr
speed 1000
no negotiation auto
isis network point-to-point
!
router isis ipfrr
net 49.0001.0140.1401.4014.00
is-type level-2-only
metric-style wide
log-adjacency-changes
nsf cisco
segment-routing mpls
segment-routing prefix-sid-map advertise-local
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2
microloop avoidance rib-update-delay 10000
!

Example 1: In the following example, local LFA is configured with linecard-disjoint and srlg-disjoint tiebreakers. Linecard-disjoint is given preference with a lower priority value (10) than the srlg-disjoint (11).

router isis access
 net 49.0001.2037.0685.b002.00
 metric-style wide
 fast-flood 10
 max-lsp-lifetime 65535
 lsp-refresh-interval 65000
 spf-interval 5 50 200
 prc-interval 5 50 200
 lsp-gen-interval 5 5 200
 log-adjacency-changes
 nsf ietf
 segment-routing mpls
 fast-reroute per-prefix level-1 all – configures the local LFA
 fast-reroute per-prefix level-2 all
 fast-reroute remote-lfa level-1 mpls-ldp - enables rLFA (optional)
 fast-reroute remote-lfa level-2 mpls-ldp
 fast-reroute ti-lfa level-1 - enables TI-LFA
 microloop avoidance rib-update-delay 10000 
 bfd all-interfaces

Example 2—Enable TI-LFA node-protecting tie-breaker on all ISIS level-2 interfaces with priority 100. All other tiebreakers are disabled.

router isis
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2 
fast-reroute tie-break level-2 node-protecting 100

Example 3—Enable TI-LFA node-protecting tie-breaker with priority 100 and TI-LFA SRLG protection with priority 200 on all IS-IS level-2 interfaces. All other tiebreakers are disabled because the node-protecting tie-breaker is configured.

router isis
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2 
fast-reroute tie-break level-2 node-protecting 100
fast-reroute tie-break level-2 srlg-disjoint 200

Example 4—Enable TI-LFA node-protecting tie-breaker with priority 100 on all ISIS level-2 interfaces except on Ethernet0/0. For those IS-IS interfaces, all other tiebreakers are disabled. Ethernet0/0 overwrites the inheritance and uses the default set of tiebreakers with linecard-disjoint, lowest-backup-path-metric, srlg-disjoint enabled.

router isis
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2 
fast-reroute tie-break level-2 node-protecting 100
!
interface ethernet0/0
ip router isis
isis fast-reroute tie-break level-2 default

Example 5—Enable TI-LFA using the default tiebreaker on all IS-IS interfaces except on Ethernet0/0. On Ethernet0/0 enable TI-LFA node-protecting with priority 100 and disable all other tiebreakers.

router isis
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2
!
interface ethernet0/0
ip router isis
isis fast-reroute tie-break level-2 node-protecting 100

Example 6—Enable TI-LFA node-protecting tie-breaker with priority 200 and linecard-disjoint tie-breaker with priority 100 on all ISIS level-2 interfaces. All other tiebreakers are disabled.

router isis
fast-reroute per-prefix level-2 all
fast-reroute ti-lfa level-2 
fast-reroute tie-break level-2 linecard-disjoint 100
fast-reroute tie-break level-2 node-protecting 200

To view tiebreakers enabled on the interface, use the following command:

show running all | section interface interface-name

To view tiebreakers enabled on the router mode, use the following command:

show running all | section router isis

In this example, 1.1.1.1 is the protecting neighbor and 4.4.4.4 is the neighbor on the protecting link.

Router# 
show ip cef 1.1.1.1
1.1.1.1/32
  nexthop 1.1.1.1 GigabitEthernet0/2/0 label [explicit-null|explicit-null]() - slot 2 is primary interface
    repair: attached-nexthop 24.0.0.2 TenGigabitEthernet0/3/0 - slot 3 is repair interface
  nexthop 24.0.0.2 TenGigabitEthernet0/3/0 label [explicit-null|explicit-null]()
    repair: attached-nexthop 1.1.1.1 GigabitEthernet0/2/0
Router# 
show ip cef 4.4.4.4
4.4.4.4/32
  nexthop 4.4.4.4 GigabitEthernet0/2/3 label [explicit-null|16004]() - slot 2 is primary interface
    repair: attached-nexthop 5.5.5.5 MPLS-SR-Tunnel2
Router# show ip cef 4.4.4.4 int
4.4.4.4/32, epoch 3, RIB[I], refcnt 6, per-destination sharing
  sources: RIB, Adj, LTE 
  feature space:
    IPRM: 0x00028000
    Broker: linked, distributed at 4th priority
    LFD: 4.4.4.4/32 2 local labels
    dflt local label info: global/877 [0x3]
    sr local label info: global/16004 [0x1B]
        contains path extension list
        dflt disposition chain 0x46654200
          label implicit-null
          FRR Primary
            <primary: IP adj out of GigabitEthernet0/2/3, addr 4.4.4.4>
        dflt label switch chain 0x46654268
          label implicit-null
          TAG adj out of GigabitEthernet0/2/3, addr 4.4.4.4
        sr disposition chain 0x46654880
          label explicit-null
          FRR Primary
            <primary: TAG adj out of GigabitEthernet0/2/3, addr 4.4.4.4>
        sr label switch chain 0x46654880
          label explicit-null
          FRR Primary
            <primary: TAG adj out of GigabitEthernet0/2/3, addr 4.4.4.4>
  subblocks:
    Adj source: IP adj out of GigabitEthernet0/2/3, addr 4.4.4.4 464C6620
      Dependent covered prefix type adjfib, cover 0.0.0.0/0
  ifnums: 
    GigabitEthernet0/2/3(11): 4.4.4.4
    MPLS-SR-Tunnel2(1022)
  path list 3B1FC930, 15 locks, per-destination, flags 0x4D [shble, hvsh, rif, hwcn]
    path 3C04D5E0, share 1/1, type attached nexthop, for IPv4, flags [has-rpr]
      MPLS short path extensions: [rib | lblmrg | srlbl] MOI flags = 0x21 label explicit-null
      nexthop 4.4.4.4 GigabitEthernet0/2/3 label [explicit-null|16004](), IP adj out of GigabitEthernet0/2/3, addr 4.4.4.4 464C6620
        repair: attached-nexthop 5.5.5.5 MPLS-SR-Tunnel2 (3C04D6B0)
    path 3C04D6B0, share 1/1, type attached nexthop, for IPv4, flags [rpr, rpr-only]
      MPLS short path extensions: [rib | lblmrg | srlbl] MOI flags = 0x1 label 16004
      nexthop 5.5.5.5 MPLS-SR-Tunnel2 label 16004(), repair, IP midchain out of MPLS-SR-Tunnel2 46CE2440
  output chain:
    label [explicit-null|16004]()
    FRR Primary (0x3B209220)
      <primary: TAG adj out of GigabitEthernet0/2/3, addr 4.4.4.4 464C6480> - primary path
      <repair:  TAG midchain out of MPLS-SR-Tunnel2 46CE22A0
                label 16()
                label 16003()
                TAG adj out of TenGigabitEthernet0/3/0, addr 24.0.0.2 46CE25E0> - repair path

Router# show isis segment-routing
 ISIS protocol is registered with MFI
 ISIS MFI Client ID:0x63
 Tag Null - Segment-Routing:
   SR State:SR_ENABLED
   Number of SRGB:1
   SRGB Start:14000, Range:1001, srgb_handle:0xE0934788, srgb_state: created
   Address-family IPv4 unicast SR is configured
     Operational state: Enabled

The command with keyword global-block displays the SRGB and the range for LSPs.

Router# show isis segment-routing global-block
IS-IS Level-1 Segment-routing Global Blocks:
System ID             SRGB Base    SRGB Range
nevada                20000        4001      
arizona             * 16000        1000      
utah                  40000        8000      

The show isis segment-routing prefix-sid-map command with keyword advertise displays the prefix-sid maps that the router advertises.

Roouter# show isis segment-routing prefix-sid-map adv
IS-IS Level-1 advertise prefix-sid maps:
Prefix               SID Index    Range        Flags
16.16.16.16/32       101          1            
16.16.16.17/32       102          1            Attached

The show isis segment-routing prefix-sid-map command with keyword receive displays the prefix-sid maps that the router receives.

Router #sh isis segment-routing prefix-sid-map receive
IS-IS Level-1 receive prefix-sid maps:
Host                 Prefix               SID Index    Range        Flags
utah                 16.16.16.16/32       101          1            
                     16.16.16.17/32       102          1            Attached

To display the connected-SIDs found in the LSPs and passed to the mapping server component, use the show isis segment-routing connected-sid command.

Router# show isis segment-routing connected-sid
IS-IS Level-1 connected-sids
Host                  Prefix               SID Index    Range        Flags
nevada              * 1.1.1.2/32           1002         1            
                      2.2.2.2/32           20           1            
                      100.1.1.10/32        10           1            
colorado              1.1.1.3/32           33           1            
                      1.1.1.6/32           6            1            
IS-IS Level-2 connected-sids
Host                 Prefix               SID Index    Range        Flags

Router# show isis fast-reroute ti-lfa tunnel
Fast-Reroute TI-LFA Tunnels:
Tunnel  Interface  Next Hop         End Point        Label     End Point Host
MP1     Et1/0      30.1.1.4         1.1.1.2          41002     nevada           
MP2     Et0/0      19.1.1.6         1.1.1.6          60006     colorado         
                                    1.1.1.2          16        nevada           
MP3     Et0/0      19.1.1.6         1.1.1.6          60006     colorado         
                                    1.1.1.2          16        nevada           
                                    1.1.1.5          70005     wyoming 

Router# show mpls traffic-eng tunnels tunnel1
Name: PE1                            (Tunnel1) Destination: 6.6.6.6
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected
    path option 10, (SEGMENT-ROUTING) type explicit IP_PATH (Basis for Setup)
  Config Parameters:
    Bandwidth: 0        kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    Path Selection:
     Protection: any (default)
    Path-invalidation timeout: 45000 msec (default), Action: Tear
    AutoRoute: enabled  LockDown: disabled Loadshare: 0 [0] bw-based
    auto-bw: disabled
    Fault-OAM: disabled, Wrap-Protection: disabled, Wrap-Capable: No
  Active Path Option Parameters:
    State: explicit path option 10 is active
    BandwidthOverride: disabled  LockDown: disabled  Verbatim: disabled
  History:
    Tunnel:
      Time since created: 4 hours, 25 minutes
      Time since path change: 4 hours, 21 minutes
      Number of LSP IDs (Tun_Instances) used: 37
    Current LSP: [ID: 37]
      Uptime: 4 hours, 21 minutes
  Tun_Instance: 37
  Segment-Routing Path Info (isis  level-1)
    Segment0[Node]: 4.4.4.4, Label: 16014
    Segment1[Node]: 5.5.5.5, Label: 16015
    Segment2[Node]: 6.6.6.6, Label: 16016
Router# show isis fast-reroute ti-lfa tunnel
 
Tag 1:
Fast-Reroute TI-LFA Tunnels:
Tunnel  Interface  Next Hop         End Point        Label     End Point Host
MP1     Gi2        192.168.1.2      6.6.6.6          16016     SR_R6            
MP2     Gi3        192.168.2.2      6.6.6.6          16016     SR_R6            
Router# show frr-manager client client-name ISIS interfaces detail
TunnelI/F : MP1
  Type : SR
  Next-hop : 192.168.1.2
  End-point : 6.6.6.6
  OutI/F : Gi2
  Adjacency State : 1
  Prefix0 : 6.6.6.6(Label : 16016)
TunnelI/F : MP2
  Type : SR
  Next-hop : 192.168.2.2
  End-point : 6.6.6.6
  OutI/F : Gi3
  Adjacency State : 1
  Prefix0 : 6.6.6.6(Label : 16016)
Router# show ip cef 6.6.6.6 internal
 
6.6.6.6/32, epoch 2, RIB[I], refcnt 6, per-destination sharing
  sources: RIB, LTE 
  feature space:
    IPRM: 0x00028000
    Broker: linked, distributed at 1st priority
    LFD: 6.6.6.6/32 1 local label
    sr local label info: global/16016 [0x1A]
        contains path extension list
        sr disposition chain 0x7FC6B0BF2AF0
          label implicit-null
          IP midchain out of Tunnel1
          label 16016
          FRR Primary
            <primary: label 16015
                      TAG adj out of GigabitEthernet3, addr 192.168.2.2>
        sr label switch chain 0x7FC6B0BF2B88
          label implicit-null
          TAG midchain out of Tunnel1
          label 16016
          FRR Primary
            <primary: label 16015
                      TAG adj out of GigabitEthernet3, addr 192.168.2.2>
  ifnums:
    Tunnel1(13)
  path list 7FC6B0BBDDE0, 3 locks, per-destination, flags 0x49 [shble, rif, hwcn]
    path 7FC7144D4300, share 1/1, type attached nexthop, for IPv4
      MPLS short path extensions: [rib | prfmfi | lblmrg | srlbl] MOI flags = 0x3 label implicit-null
      nexthop 6.6.6.6 Tunnel1, IP midchain out of Tunnel1 7FC6B0BBB440
  output chain:
    IP midchain out of Tunnel1 7FC6B0BBB440
    label [16016|16016]
    FRR Primary (0x7FC714515460)
      <primary: label 16015
                TAG adj out of GigabitEthernet3, addr 192.168.2.2 7FC6B0BBB630>
      <repair:  label 16015
                label 16014
                TAG midchain out of MPLS-SR-Tunnel1 7FC6B0BBAA90
                label 16016
                TAG adj out of GigabitEthernet2, addr 192.168.1.2 7FC6B0BBBA10>

Note	To ensure a less than 50 msec traffic protection with TI-LFA, SR-TE with dynamic path option must use the backup adjacency SID.

To create an SR-TE with dynamic path option, use the following configuration on every router in the topology:

router isis 1
fast-reroute per-prefix level-1 all

At the tunnel head-end router:

interface Tunnel1
ip unnumbered Loopback1
tunnel mode mpls traffic-eng
tunnel destination 6.6.6.6
tunnel mpls traffic-eng autoroute announce
tunnel mpls traffic-eng path-option 1 dynamic segment-routing
tunnel mpls traffic-eng path-selection segment-routing adjacency protected