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Cisco Bug: CSCvu65524 - ISIS does not enforce Weighted Remote SRLG backup Path in certain scenario

Last Modified

Oct 05, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

7.3.1.BASE

Description (partial)

Symptom:
A Weighted Remote SRLG back up path is not chosen correctly in the following case:

Topology

     10
R1-----R2------R3
 \        /               |
  \      /                | 10
   \    /                 |
    R6------------R7

SRLG Value of 10 is configured on link  between R1 and R2 AND R7 and R3. WSRLG is enabled on R1.
Primary Path is R1—R2---R3. WSRLG back up path chosen is via R6. we should have enforced the WSRLG backup Path via R2. 

r1#sh isis fast-reroute 3.3.3.3/32 detail 

L2 3.3.3.3/32 [30/115] Label: 16103, medium priority
     via 12.0.0.2, TenGigE0/0/1/0, Label: 16103, hulk_exr-asr2, SRGB Base: 16000, Weight: 0
       Backup path: LFA, via 16.0.0.6, TenGigE0/0/1/3, Label: 16103, r6, SRGB Base: 16000, Weight: 0, Metric: 40
       P: No, TM: 40, LC: No, NP: No, D: No, SRLG: Yes
     src hulk_exr-asr3.00-00, 3.3.3.3, prefix-SID index 103, R:0 N:1 P:0 E:0 V:0
         L:0, Alg:0
r1#

Conditions:
ISIS configured to use fast reroute with weighted remote SRLG
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