[c-nsp] auto-backup tunnels

[Koltsov, Aleksey (NSN - DE/Dusseldorf)]

Hello Folks,
 
I have a question regarding mpls-te auto-backup tunnels. I play with a
network like below one, where I run mpls-te with FRR:
 
PE     P      P      PE
 
R1----R2-----R3-----R4
|        |        |         |
|        |        |         |
|        |        |         |
R5----R6-----R7-----R8
 

There are full-mash primary tunnels (like R1->R4/R8 so on) and to build
backup tunnels - auto-backup tunnels feature is used:
 
mpls traffic-eng tunnels 
mpls traffic-eng auto-tunnel backup 
mpls traffic-eng auto-tunnel backup config unnumbered-interface
Loopback0 
mpls traffic-eng auto-tunnel backup timers removal unused 3600 0 
mpls traffic-eng auto-tunnel backup tunnel-num min 8000 max 9999 
 
So, as it could be seen from the config above, both NHOP and NNHOP
backup tunnels are setup. But when I crash the network like to shutdown
R2 and R3 I can see that, for example, R1 builds a backup tunnel from R1
to R4 which is neither NHOP nor NNHOP tunnel. So here is my question why
it happens? Is it expected behaviour or not?
 
 
BR,
Aleksey Koltsov