Network Virtualization and Data Center Fabrics
This domain tests overlay networking and fabric design: VXLAN encapsulation, EVPN control plane, VLT multi-chassis aggregation, spine-leaf topology and automated fabric services in OS10.
VXLAN
A VTEP encapsulates the original frame in UDP with an 8-byte VXLAN header containing a 24-bit VNI, destination port 4789. The underlay is routed IP, so VTEP loopback addresses must be reachable and ECMP-friendly; the overlay provides Layer 2 stretch. VNI and VLAN are independent - the mapping exists only locally on each VTEP. Allow for the extra overhead by raising MTU across the underlay.
EVPN
MP-BGP address family L2VPN EVPN distributes MAC/IP reachability. Type 2 carries MAC/IP pairs, type 3 provides inclusive multicast (IMET) for BUM traffic, type 5 carries IP prefixes for symmetric routing. An anycast distributed gateway lets every leaf route on behalf of a subnet, avoiding traffic tromboning. VRFs provide multi-tenancy separation.
VLT
Two switches form one logical endpoint: a VLTi peer link, a backup heartbeat link, matching VLT domain IDs and dual-homed LACP server links. VLT removes the need to run spanning tree toward dual-homed servers; orphan ports are those not yet dual-connected.
Fabrics
Spine-leaf with routed ECMP underlay scales horizontally. SmartFabric Services in OS10 automates VLAN, VXLAN and EVPN provisioning, including MX7000 modular environments.
Worked example
A VM on leaf-1 in VLAN 100 (VNI 10100) pings a VM on leaf-2. Leaf-1 maps VLAN 100 to VNI 10100 locally, encapsulates toward leaf-2's VTEP loopback, and advertises its MAC/IP via EVPN type 2 so leaf-2 knows where to send the return frame. Neither the spines nor the underlay learn the tenant MAC addresses.
Traps
Believing VXLAN needs a Layer 2 underlay; mismatched VLT domain IDs or backup link failures; forgetting MTU overhead so large frames drop; assuming VNI must equal VLAN ID; treating the VLTi as a general data path for all north-south traffic.