Consider the following scenario:
- Customer A is a customer of SP A
- SP A is a customer of SP B
- SP B has a traffic engineering community implementation
With regards to using BGP communities for TE:
- Does SP A write their own community implementation that maps to (some portion
of) the community implementation of SP B?
- Does SP A write their own community implementation that has no mappings at
all to the community implementation of SP B; any TE that is required to be
pushed to SP B is done by some dialog and coordination between Customer A and
- Does SP A allow Customer A to announce prefixes tagged with SP B’s
- Is this sort of thing really complicated today, but one of the goals of
 Customer A has knowledge of SP A’s upstream SP B
 This opens up a can of worms where SP A or SP B implements some communities
prefixed with reserved ASes, so we’ll assume that SP A implements some method
of allowing communities prefixed with ASes of SP A and SP B only.