Hello epaniagua,
Thank you for this answer. Here is the output of the command :
>show route table PRA-MF.inet.0
PRA-MF.inet.0: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
192.168.5.0/24 *[Direct/0] 12w6d 16:20:10
> via reth0.300
192.168.5.254/32 *[Local/0] 12w6d 16:20:10
Local via reth0.300
192.168.6.0/24 *[Direct/0] 12w6d 16:20:10
> via reth0.301
192.168.6.254/32 *[Local/0] 12w6d 16:20:10
Local via reth0.301
Your solution seems to be correct, after adding the rib-groups I am now able to ping the internet. I've marked your post as the solution.
Thank you very much for your help, I thought I'd have gone crazy at this rate.