Architecture choices:
ERB: more East and west traffic of the same box , lower latency , Leaf has more feature / may be higher cost
CRB: more traffic between leaves , Less feature , Leaf could be lower cost
CRB-Access, CRB-Gateway, DC-Gateway, ERB-UCAST-Gateway, and CRB-MCAST-Gateway roles overlay roles
Centrally-Routed Bridging Overlay Design and Implementation
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