Why do you need to RT’s for Routes in Same VRF?
Why do you need to import/export RTs for sites that have same RD/VRF in order to allow them to communicate with eachother? For example, say that you have two customers, 1 and 2, and two sites per customer, A, B, C, and D. Each site has its own PE-CE connection that goes into the MPLS “core”.
Customer 1 has sites A and B with an RD of 1:1.
Customer 2 has sites C and D with an RD of 1:2.
My understanding is that in order to get sites A/B to communicate with each other, one would need to use RTs to import/export 1:1. The same would be true in order to get sites C/D to communicate with each other.
If sites A/B share the same RD, how come routes advertised by each site are not implicitly imported into the VRFs of their respective sites PE routers? For example, when site A advertises a route to its PE, and that PE advertises the route to the site B PE, without the RTs setup, the site B PE will not import the site A PE learned route even though the RD is the same as a locally configured VRF.
Are RDs of local significance only and RTs of global significance? That is the only thing I can come up with that makes sense for the aforementioned behavior.
Thank you for your input.