In the previous post we have seen how does "Segment Routing - Ti-LFA - Adjacency Sid Protection - Link Protection" works when Segment Routing is enabled. The main advantage of using Ti-LFA link protection is that primary link is excluded during post convergence backup path calculations. Ti-LFA Link protection provides 50ms resilience during the time of failure of link. There might be possibility of link failure due to node failure but XR-11 will never come to know till IGP convergence is completed.
Now node xr-11 can calculate the backup path by using TI-LFA node protection which provides protection from neighbor node failures. The neighbor node (XR-1) is excluded during the post convergence backup path calculation.
As per previous post, Ti-LFA node protection is already configured and now we will be configuring Ti-LFA node protection.
router isis 1
!
interface GigabitEthernet0/0/0/0
point-to-point
address-family ipv4 unicast
fast-reroute per-prefix
fast-reroute per-prefix ti-lfa
fast-reroute per-prefix tiebreaker node-protecting index 100 -> Ti-LFA Node Protection With Priority 100
metric 500
!
!
interface GigabitEthernet0/0/0/1
point-to-point
address-family ipv4 unicast
fast-reroute per-prefix
fast-reroute per-prefix ti-lfa
fast-reroute per-prefix tiebreaker node-protecting index 100 -> Ti-LFA Node Protection With Priority 100
metric 500
!
Point To Remember
Both link-protecting and node-protecting TI-LFA backup paths will be computed. If the priority(index) associated with the node-protecting tiebreaker is higher than any other tiebreakers, then node-protecting post-convergence backup paths will be selected, if it is available.
Verify below configuration which shows that node protection post-convergence backup is selected. Now instead XR-1, XR-6 is selected. For more details on PQ Node, refer to post "Segment Routing - Topology Independent LFA"
RP/0/0/CPU0:xrvr-11#show isis fast-reroute 1.1.1.12/32 detail
L2 1.1.1.12/32 [1020/115] medium priority
via 99.1.11.1, GigabitEthernet0/0/0/0, xrvr-1, SRGB Base: 16000, Weight: 0
Backup path: TI-LFA (node), via 99.5.11.5, GigabitEthernet0/0/0/1 xrvr-5, SRGB Base: 16000, Weight: 0
P node: xrvr-5.00 [1.1.1.5], Label: ImpNull
Q node: xrvr-6.00 [1.1.1.6], Label: 24001
Prefix label: 16012
P: No, TM: 1050, LC: No, NP: Yes, D: Yes, SRLG: No
src xrvr-12.00-00, 1.1.1.12, prefix-SID index 12, R:0 N:1 P:0 E:0 V:0 L:0
RP/0/0/CPU0:xrvr-11#
Check the routing table to verify that backpath is installed or not:
RP/0/0/CPU0:xrvr-11#show route 1.1.1.12/32 detail
Routing entry for 1.1.1.12/32
Known via "isis 1", distance 115, metric 1020, labeled SR, type level-2
Installed May 30 17:49:13.744 for 00:04:26
Routing Descriptor Blocks
99.1.11.1, from 1.1.1.12, via GigabitEthernet0/0/0/0, Protected
Route metric is 1020
Label: 0x3e8c (16012)
Tunnel ID: None
Binding Label: None
Extended communities count: 0
Path id:1 Path ref count:0
NHID:0x6(Ref:24)
Backup path id:65
99.5.11.5, from 1.1.1.12, via GigabitEthernet0/0/0/1, Backup (TI-LFA)
Repair Node(s): 1.1.1.5, 1.1.1.6
Route metric is 1050
Labels: 0x100004 0x5dc1 0x3e8c (1048580 24001 16012) -> 1048580 label is used for impicit null
Tunnel ID: None
Binding Label: None
Extended communities count: 0
Path id:65 Path ref count:1
NHID:0x5(Ref:24)
Route version is 0x3d (61)
Local Label: 0x3e8c (16012)
IP Precedence: Not Set
QoS Group ID: Not Set
Flow-tag: Not Set
Fwd-class: Not Set
Route Priority: RIB_PRIORITY_NON_RECURSIVE_MEDIUM (7) SVD Type RIB_SVD_TYPE_LOCAL
Download Priority 1, Download Version 838
No advertising protos.
RP/0/0/CPU0:xrvr-11#
Veriy CEF table and match the labels imposed with the above mentioned labels.
RP/0/0/CPU0:xrvr-11#show cef 1.1.1.12/32
Sat May 30 17:54:39.252 UTC
1.1.1.12/32, version 838, labeled SR, internal 0x1000001 0x81 (ptr 0xa12fcb8c) [2], 0x0 (0xa12e1cd4), 0xa28 (0xa18b61dc)
Updated May 30 17:49:13.764
local adjacency 99.1.11.1
Prefix Len 32, traffic index 0, precedence n/a, priority 1
Extensions: context-label:16012
via 99.1.11.1/32, GigabitEthernet0/0/0/0, 11 dependencies, weight 0, class 0, protected [flags 0x400]
path-idx 0 bkup-idx 1 NHID 0x0 [0xa18d05d0 0xa18d00e4]
next hop 99.1.11.1/32
local label 16012 labels imposed {16012}
via 99.5.11.5/32, GigabitEthernet0/0/0/1, 11 dependencies, weight 0, class 0, backup (TI-LFA) [flags 0xb00]
path-idx 1 NHID 0x0 [0xa15fd560 0xa15fd4a8]
next hop 99.5.11.5/32, Repair Node(s): 1.1.1.5, 1.1.1.6 -> Verify Repair Nodes. Node 1 is not coming in the path
local adjacency
local label 16012 labels imposed {ImplNull 24001 16012}
RP/0/0/CPU0:xrvr-11#
With maximum of 3 transport labels, we can reach to the destination.
Here is the beginning of my post. And here is the rest of it.
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