VTI tunnel issue

[AndreyPokorskiy]

Hello !
I experienced a strange issue with VT
We have tree routers connected via VTIs:
R1 Tunnel52<--->Tunnel21 [Backup] BR Tunnel22<------> Tunnel52 R2
R1 is connected to another location through multiple VTI tunnels, all of which utilize the same physical interface as their source. Meanwhile, BR has two VTI tunnels, Tunnel21 (backup) and Tunnel22, both of which have the same physical interface as their source. Interestingly, only Tunnel21 encounters frequent flapping.
BR is cisco C1111 16.12(2r) router 
The virtual backup connection between BR Tunnel21 and R1 Tunnel52 seems to be experiencing intermittent connectivity issues with no traffic passing through. On the other hand, the active Tunnel22, which handles all the traffic, is functioning without any problems. We have thoroughly examined the syslogs for physical interfaces and ISP circuits, but there are no indications of errors or faults.
I would really appreciate any thoughts or ideas you have!
Thank you!
Sincerely,

Andrey P.

[liviu.gheorghe]

Hello @AndreyPokorskiy ,

can you provide the following outputs:

show interface Tunnel 52 and show running-config interface Tunnel 52 from router R1

show interface Tunnel52 and show running-config interface Tunnel 52 from router R2

show interface Tunnel21 and show running-config interface Tunnel 21 from router BR

show interface Tunnel22 and show running-config interface Tunnel 22 from router BR

[MHM Cisco World]

can you draw topology 

MHM