About this EVPN and VXLAN calculator
Describe a VXLAN EVPN fabric once — AS number, leaf count, tenants and their VLANs — and it allocates an L2 VNI per VLAN and an L3 VNI per VRF, builds Type 1 route distinguishers from each leaf’s router ID, derives route targets, and estimates how many routes each switch holds. The MTU panel sizes the underlay: VXLAN adds 50 bytes over IPv4 and 70 over IPv6, and Juniper counts the Ethernet header where Cisco, Arista and NVIDIA do not. Configuration covers the overlay only.
Common questions
How much MTU does VXLAN need?
VXLAN over IPv4 adds 50 bytes: 14 for the outer Ethernet header, 20 for IP, 8 for UDP and 8 for VXLAN. To carry 1500-byte frames the underlay needs an MTU of at least 1550. Many fabrics use about 9000 on the underlay to leave room for jumbo frames.
What is the difference between an L2 VNI and an L3 VNI?
An L2 VNI maps to a VLAN and bridges traffic within one broadcast domain. An L3 VNI maps to a VRF and carries routed traffic between subnets, as used by symmetric IRB.
What is the difference between a route distinguisher and a route target?
A route distinguisher makes a route unique in BGP, so overlapping tenants do not collide. A route target controls which VRFs and VLANs import it. The RD identifies a route, and the RT decides where it goes.