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Multicast packets being dropped due to out of sync between PIM and Rtmgr process after introducing new best route.

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TitleMulticast packets being dropped due to out of sync between PIM and Rtmgr process after introducing new best route.
Symptoms
Out of sync between PIM and Rtmgr process after introducing new best route. Due to this out of sync, multicast packets being dropped because of RPF failure.

Replication steps are below,
   Ixia(4/1)  ------ SW1 ------ SW2 ---- hub
                                 |
                                 |
                              Ixia(4/2)


1) Have created OSPF and BGP adjacency between both Ixia ports and SW1.
2) Advertising the route 10.41.10.0/24, 10.41.15.0/24, 10.51.10.0/24, 10.51.15.0/24 routes from both BGP neighbors.
3) Start OSPF, BGP protocol from Ixia(4/1) and PIM cache will be looks like below,
X670-48x.1 # sh iproute 10.0.0.0/8
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
#bi  10.41.10.0/24      192.0.2.1  0    UG-D---um--f- VLAN01   0d:0h:2m:11s  <- Nexthop: 192.0.2.1 and VLAN: VLAN01
#bi  10.41.15.0/24      192.0.2.1  0    UG-D---um--f- VLAN01   0d:0h:2m:11s
#bi  10.51.10.0/24      192.0.2.1  0    UG-D---um--f- VLAN01   0d:0h:2m:11s
#bi  10.51.15.0/24      192.0.2.1  0    UG-D---um--f- VLAN01   0d:0h:2m:11s
#bi  10.53.1.0/24       192.0.2.1  0    UG-D---um--f- VLAN01   0d:0h:2m:12s
#d   10.100.10.97/32    10.100.10.97    1    U------um--f- Lo1        2d:19h:13m:41s

X670-48x.2 # show pim ipv4 cache
Index  Dest Group      Source             InVlan   Origin
[0000] 239.1.12.1      10.41.10.2 ( )     VLAN01 Sparse   <- It is showing proper ingress VLAN.      
[0000] 239.1.12.1      10.41.15.2 ( )     VLAN01 Sparse        
[0000] 239.1.12.1      10.51.10.2 ( )     VLAN01 Sparse        
[0000] 239.1.12.1      10.51.15.2 ( )     VLAN01 Sparse        

Number of multicast cache = 4

We see out of sync between PIM and Rtmgr after initiating the OSPF and BGP protocol on Ixia(4/2).

X670-48x.10 # sh iproute 10.0.0.0/8
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
#bi  10.41.10.0/24      198.51.100.1  0    UG-D---um--f- VLAN02    0d:0h:6m:45s  <- Nexthop: 198.51.100.1 and VLAN: VLAN02
#bi  10.41.15.0/24      198.51.100.1  0    UG-D---um--f- VLAN02    0d:0h:6m:45s
#bi  10.51.10.0/24      198.51.100.1  0    UG-D---um--f- VLAN02    0d:0h:6m:45s
#bi  10.51.15.0/24      198.51.100.1  0    UG-D---um--f- VLAN02    0d:0h:6m:45s
#bi  10.53.1.0/24       198.51.100.1  0    UG-D---um--f- VLAN02    0d:0h:6m:46s

X670-48x.11 # show pim ipv4 cache
Index  Dest Group      Source             InVlan   Origin
[0000] 239.1.12.1      10.41.10.2 ( )     VLAN01 Sparse    <- It is showing wrong vlan. !!ISSUE!!    
[0000] 239.1.12.1      10.41.15.2 ( )     VLAN01 Sparse        
[0000] 239.1.12.1      10.51.10.2 ( )     VLAN01 Sparse        
[0000] 239.1.12.1      10.51.15.2 ( )     VLAN01 Sparse
Environment
  • All EXOS platforms
  • EXOS 16.1
  • BGP/PIM
Cause
The issue can be exposed due to software defect xos0064357.
Resolution
Upgrade to 16.1.3.6-patch1-8, 21.1.1.4-patch1-5 or later releases where xos0064357 is fixed.
Additional notes

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