Network
Layer 2 high availability
vPC makes two Nexus switches act as one logical switch. The peer-link is a port channel carrying flooded and unknown-unicast traffic plus control PDUs; the peer-keepalive link is a heartbeat path and never carries data. Configuration consistency checks decide the outcome: Type-1 mismatches (MTU, STP mode, and similar) suspend the vPC and bring member ports down; Type-2 mismatches only raise a warning. Also know peer-gateway, ARP synchronization, and orphan ports used by single-homed devices.
Overlay
VXLAN encapsulates Layer 2 frames in UDP 4789 between VTEPs, with EVPN as the MP-BGP control plane. Memorize the route types: type 2 (MAC/VNI and MAC/IP), type 3 (inclusive multicast Ethernet tag for BUM traffic), type 5 (IP prefix). Anycast gateway lets the same SVI and IP/MAC exist on every leaf, so a VM keeps its default gateway after vMotion. ARP suppression answers requests from the local EVPN table instead of flooding.
Extending Layer 2 between sites
OTV uses a join interface (underlay IGP) plus an overlay interface where the site VLAN and extended VLANs are configured. An Adjacency Server forms the overlay in multicast mode; the authoritative edge device handles STP isolation.
Rule of thumb
Size the VXLAN underlay MTU at 1554 bytes or more on every link and raise the IP MTU on VTEP SVIs. VXLAN does not fragment, so a DF-set ping of 1554 bytes is a fast end-to-end verification.