If ES has more than one VLAN, the DF roles are load-balanced between leaf nodes, i.e. DF for VLAN 10 is Leaf-102 and DF for VLAN 11 is Leaf-104. The selection process uses the formula “i = V mod N”, where V represents VLAN Id and N represents a number of leaf switches in the redundancy group. The “i” is an ordinal of a leaf switch in the redundancy group. When Leaf-102 and Leaf-103 exchange BGP L2VPN EVPN Route-Type 4 (Ethernet Segment Route) their IP address is included in NLRI. Each switch sets these IP address learned from BGP Update in numerical order from lowest to highest. In the case of Leaf-102 and Leaf-103, the order is
192.168.100.102,
192.168.100.103. The lowest IP i.e.
192.168.100.102 gets ordinal zero (0) and the next one gets ordinal one (1) and so on.
Formula to calculate DF for VLAN 10 is
V mod N = i