It's possible to use a 32-bit ASN in set community and the CLI doesn't complain, but FRR does.
dmbaturin@reki# set policy route-map flag-blackhole rule 3 set community 65551:666 [edit] dmbaturin@reki# commit [ policy route-map flag-blackhole rule 3 set community 65551:666 ] You must specify an action [[policy route-map flag-blackhole]] failed Commit failed
The easiest thing to do is to disallow large communities in set community, but I wonder if we can make it use the correct command depending on the ASN size...